WO2022177990A2

WO2022177990A2 - Modified sars-cov-2 spike polypeptides and nanoparticles thereof

Info

Publication number: WO2022177990A2
Application number: PCT/US2022/016597
Authority: WO
Inventors: Brian Pierce; Kelly Lyn Warfield
Original assignee: Emergent Product Development Gaithersburg Inc.
Priority date: 2021-02-17
Filing date: 2022-02-16
Publication date: 2022-08-25
Also published as: WO2022177990A3

Abstract

The present disclosure is directed to modified coronavirus (e.g., SARS-CoV-2) spike polypeptides, nanoparticles comprising the same, methods of using the same, e.g., to generate coronavirus (e.g., SARS-CoV-2) neutralizing antibodies or antigen-binding fragments thereof. The disclosure also provides methods of using neutralizing antibodies or antigen-binding fragments thereof obtained by such methods (e.g., equine antibodies or antigen-binding fragments thereof) to treat or prevent coronavirus (e.g., SARS-CoV-2) infections in a subject.

Description

MODIFIED SARS-COV-2 SPIKE POLYPEPTIDES AND NANOPARTICLES THEREOF CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims the priority benefit of U.S. Provisional Application No. 63/150,454, filed February 17, 2021, which is hereby incorporated by reference herein in its entirety. REFERENCE TO A SEQUENCE LISTING SUBMITTED ELECTRONICALLY VIA EFS-WEB [0002] The Sequence Listing submitted February 16, 2022, as a text file named “2479.224PC01_Seqlisting_ST25,” created on February 2, 2022, and having a size of 50,104 bytes, is hereby incorporated by reference. BACKGROUND Field [0003] Provided herein are modified coronavirus spike polypeptides (e.g., SARS-CoV-2 spike polypeptides), nanoparticles comprising the same, and methods of using the same, e.g., for the production of antibodies or fragments thereof that bind and/or neutralize coronavirus (e.g., SARS-CoV-2). Background [0004] Coronaviruses are a family of viruses that can cause respiratory tract illnesses, like the common cold. However, new coronaviruses that have emerged from animal reservoirs have caused serious and widespread illness and death, including SARS-CoV, MERS-CoV, and SARS-CoV-2. SARS-CoV-2 causes the highly infectious Coronavirus Disease 2019 (COVID-19), which the World Health Organization declared a global pandemic in March of 2020. There is an urgent and immediate need for effective therapeutic options for the treatment of individuals with COVID-19, e.g., therapeutic options that can improve clinical outcomes by addressing viral infection and resolving illness or reducing progression of the disease. [0005] Attempts have been made to develop nanoparticles containing viral proteins in various scaffolds for treating other viral infections such as influenza. Such nanoparticles can be designed to present various different antigens, and there are currently many different particles being evaluated as antigen carriers, including inorganic and polymeric nanoparticles, virus-like particles (VLPs), liposomes and self-assembled protein nanoparticles. However, it is currently unknown what coronavirus antigens in what nanoparticle structures would provide an effective tool for generating clinically useful immune responses. [0006] Therefore, there remains a need for effective coronavirus vaccines and methods of generating neutralizing anti-coronavirus compositions. BRIEF SUMMARY [0007] Provided herein are proteins comprising modified coronavirus (e.g., SARS-CoV- 2) spike polypeptides that can be presented to an immune system (e.g., in the form of nanoparticles) to generate an effective coronavirus neutralizing immune response (e.g., antibodies and antigen-binding fragments thereof). Methods of using such proteins and nanoparticles containing such proteins are also provided. [0008] In some aspects, a protein provided herein comprises (i) a coronavirus spike polypeptide or a fragment thereof and (ii) a modified ferritin polypeptide or fragment thereof, wherein the coronavirus spike polypeptide or a fragment thereof and the modified ferritin polypeptide or fragment thereof are fused, and wherein the modified ferritin polypeptide or fragment thereof comprises a mutation that removes an N-linked glycosylation site. [0009] In some aspects, the coronavirus spike polypeptide or fragment thereof is a modified coronavirus spike polypeptide or fragment thereof. In some aspects, the modified coronavirus spike polypeptide or fragment thereof is capable of binding to ACE2 and (i) comprises a mutation that reduces or eliminates furin cleavage and/or (ii) comprises a mutation that stabilizes a pre-fusion conformation of the polypeptide or fragment there. In some aspects, the mutation that reduces or eliminates furin cleavage comprises a substitution of the amino acid corresponding to R685 in SEQ ID NO:5. In some aspects, the coronavirus spike polypeptide or fragment thereof is a naturally occurring coronavirus spike polypeptide or fragment thereof. [0010] In some aspects, a protein provided herein comprises a modified coronavirus spike polypeptide or a fragment thereof, wherein the spike polypeptide or fragment thereof (i) is capable of binding to ACE2, (ii) comprises a mutation that reduces or eliminates furin cleavage, wherein the mutation that reduces or eliminates furin cleavage comprises a substitution of the amino acid corresponding to R685 in SEQ ID NO:5, and (iii) comprises a mutation that stabilizes a pre-fusion conformation of the polypeptide or fragment thereof. In some aspects, the protein further comprises a ferritin polypeptide or fragment thereof fused to the modified coronavirus spike polypeptide or fragment thereof. In some aspects, the ferritin polypeptide or fragment thereof is a modified ferritin polypeptide or fragment thereof. In some aspects, the modified ferritin polypeptide or fragment thereof comprises a mutation that removes an N-linked glycosylation site. In some aspects, the ferritin polypeptide or fragment thereof is a naturally occurring ferritin polypeptide or fragment thereof. [0011] In some aspects, the coronavirus is severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). [0012] In some aspects, the mutation that reduces or eliminates furin cleavage does not comprise a deletion of any amino acids corresponding to R682 to R685 in SEQ ID NO:5. In some aspects, the mutation that reduces or eliminates furin cleavage consists of a substitution of the amino acid corresponding to R685 in SEQ ID NO:5. In some aspects, the amino acid corresponding to R685 in SEQ ID NO:5 is substituted with an alanine (A). [0013] In some aspects, the mutation that stabilizes a pre-fusion conformation comprises a mutation of the amino acid corresponding to K986 and/or the amino acid corresponding to V987 in SEQ ID NO:5. In some aspects, the mutation that stabilizes a pre-fusion conformation consists of a mutation of the amino acid corresponding to K986 to proline (P) in SEQ ID NO:5 and a mutation of the amino acid corresponding to V987 to proline (P) in SEQ ID NO:5. [0014] In some aspects, the modified coronavirus spike polypeptide or fragment thereof is at least 90%, 95%, 96%, 97%, 98%, or 99% identical to amino acids 16-1,208 of SEQ ID NO:2. In some aspects, the modified coronavirus spike polypeptide or fragment thereof comprises 2-10, 2-8, 2-6, 2-5, 2-4, or 2-3 mutations as compared to amino acids 16-1,208 of SEQ ID NO:2. In some aspects, the 2-10, 2-8, 2-6, 2-5, 2-4, or 2-3 mutations are amino acid substitutions. [0015] In some aspects, the modified coronavirus spike polypeptide or fragment thereof is at least 1000 amino acids in length, at least 1050 amino acids in length, at least 1100 amino acids in length, at least 1150 amino acids in length, at least 1175 amino acids in length, or at least 1190 amino acids in length. [0016] In some aspects, the modified coronavirus spike polypeptide or fragment thereof comprises the amino acid sequence of amino acids 16-1,208 of SEQ ID NO:2. [0017] In some aspects, the modified coronavirus spike polypeptide or fragment thereof is no more than 1250 amino acids in length, no more than 1225 amino acids in length, no more than 1210 amino acids in length, or no more than 1,195 amino acids in length. [0018] In some aspects, the modified coronavirus spike polypeptide or fragment thereof is about 1150 to about 1210 amino acids in length. [0019] In some aspects, the protein does not comprise amino acids 1209-1273 of SEQ ID NO:5. [0020] In some aspects, the ferritin polypeptide or fragment thereof is a Helicobacter pylori ferritin polypeptide or fragment thereof or wherein the modified ferritin polypeptide or fragment thereof is a modified Helicobacter pylori ferritin polypeptide or fragment thereof. [0021] In some aspects, the mutation that removes an N-linked glycosylation site comprises a substitution of the amino acid corresponding to N19 in SEQ ID NO:7. In some aspects, the amino acid corresponding to N19 in SEQ ID NO:7 is substituted with an glutamine (Q). [0022] In some aspects, the ferritin polypeptide or fragment thereof or the modified ferritin polypeptide or fragment thereof is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of SEQ ID NO:3. In some aspects, the ferritin polypeptide or fragment thereof or the modified ferritin polypeptide or fragment thereof comprises the amino acid sequence of SEQ ID NO:3. [0023] In some aspects, the coronavirus spike polypeptide or fragment thereof or the modified coronavirus spike polypeptide or fragment thereof is C-terminal to the ferritin polypeptide or fragment thereof or the modified ferritin polypeptide or fragment thereof. [0024] In some aspects, the coronavirus spike polypeptide or fragment thereof or the modified coronavirus spike polypeptide or fragment protein and the ferritin polypeptide or fragment thereof or the modified ferritin polypeptide or fragment thereof are fused via a linker. In some aspects, the linker is a polypeptide. In some aspects, the linker polypeptide is a glycine-serine polypeptide. [0025] The protein of claim 32 or 33, wherein the linker polypeptide is about 2 to about 5 or about 2 to about 3 amino acids in length. In some aspects, the linker comprises the amino acid sequence of SEQ ID NO:4. [0026] In some aspects, the coronavirus spike polypeptide or fragment thereof or the modified coronavirus spike polypeptide or fragment protein is fused directly to the ferritin polypeptide or fragment thereof or the modified ferritin polypeptide or fragment thereof. [0027] In some aspects, a protein provided herein comprises amino acids 16-1,376 of SEQ ID NO:6 or comprises the amino acid sequence of SEQ ID NO:6. [0028] In some aspects, the protein is capable of self-assembling into a nanoparticle comprising a core and an outer portion, wherein the ferritin polypeptide or fragment thereof or the modified ferritin polypeptide or fragment thereof forms the core and the coronavirus spike polypeptide or fragment thereof or the modified coronavirus spike polypeptide or fragment protein forms the outer portion. [0029] In some aspects, a trimer provided herein comprises any protein provided herein. [0030] In some aspects, a trimer provided herein comprises three monomers, wherein each of the three monomers comprises any protein provided herein. [0031] In some aspects, a nanoparticle provided herein comprises any protein or trimer provided herein. In some aspects, a nanoparticle provided herein trimers, wherein each trimer is a trimer provided herein. The nanoparticle of claim 41 or 42, wherein the nanoparticle displays trimers on its surface. In some aspects, the nanoparticle comprises 8 trimers. In some aspects, the nanoparticle has octahedral symmetry. In some aspects, the nanoparticle has a hydrodynamic radius of about 20 to about 60 or about 35 to about 50 nanometers as measured by dynamic light scattering. In some aspects, the nanoparticle comprises a ferritin core that has a radius of about 12 nanometers as measured by transmission electron microscopy. In some aspects, the nanoparticle comprises a core and an outer portion, wherein the ferritin polypeptide or fragment thereof or the modified ferritin polypeptide or fragment thereof forms the core and the coronavirus spike polypeptide or fragment thereof or the modified coronavirus spike polypeptide or fragment protein forms the outer portion [0032] In some aspects, a protein, trimer, or nanoparticle provided herein is capable of binding to ACE2. [0033] In some aspects, a protein, trimer, or nanoparticle provided herein is isolated. [0034] In some aspects, a protein, trimer, or nanoparticle provided herein is capable of eliciting an immune response to the modified coronavirus spike polypeptide or a fragment thereof in a mammal, optionally wherein the mammal is a horse. In some aspects, the immune response is capable of neutralizing a wild-type coronavirus in an in vitro infection assay, optionally wherein the wild-type coronavirus is wild-type SARS-CoV-2. [0035] In some aspects, a nucleic acid provided herein comprises a polynucleotide sequence encoding any protein provided herein. [0036] In some aspects, a nucleic acid provided herein comprises a polynucleotide comprising nucleotides 905-5032 of SEQ ID NO:1. In some aspects, a nucleic acid provided herein comprises a polynucleotide comprising the nucleic acid sequence of SEQ ID NO:1. [0037] In some aspects, a vector provided herein comprises any nucleic acid provided herein. In some aspects, the vector further comprises a promoter. In some aspects, the promoter is a CMV promoter. [0038] In some aspects, a host cell provided herein comprises any nucleic acid or vector provided herein. In some aspects, the host cell is a 293 cell or a 293F cell. [0039] In some aspects, a method of producing a trimer or a nanoparticle provided herein comprises culturing any host cell provided herein under conditions suitable for the assembly of a trimer or nanoparticle. In some aspects, the method further comprises isolating the trimer or the nanoparticle from the cell culture, optionally wherein the isolating comprises anion exchange chromatography and/or size exclusion chromatography. [0040] In some aspects, a trimer or nanoparticle provided herein is produced by any method of producing a trimer or nanoparticle provided herein. [0041] In some aspects, an immunogenic composition provided herein comprises any protein, trimer, or nanoparticle provided herein. [0042] In some aspects, a pharmaceutical composition provided herein comprises any protein, trimer, or nanoparticle provided herein and a pharmaceutically acceptable excipient. [0043] In some aspects, a vaccine composition provided herein comprises any protein, trimer, or nanoparticle provided herein. [0044] In some aspects of a composition provided herein, at least 95% of trimers in the composition are in pre-fusion conformation. In some aspects, the composition further comprises an adjuvant. [0045] In some aspects, a method of vaccinating an animal provided herein comprises administering any protein, trimer, nanoparticle, or composition provided herein such that the animal produces an immune response against the protein, trimer, or nanoparticle. In some aspects, the immune response is capable of neutralizing wild-type coronavirus in an in vitro infection assay, optionally wherein the wild-type coronavirus is wild-type SARS- CoV-2. In some aspects, the immune response is capable of neutralizing a coronavirus pseudovirus with spike protein in an in vitro infection assay, optionally wherein the coronavirus pseudovirus is a SARS-CoV-2 pseudovirus with a SARS-CoV-2 spike protein. [0046] In some aspects, a method of making antibodies or antigen-binding fragments thereof that specifically bind to the spike protein of a coronavirus provided herein comprises administering any protein, trimer, nanoparticle, or composition provided herein to an animal such that the animal produces antibodies or antigen-binding fragments thereof that bind to the protein, trimer, or nanoparticle, optionally wherein the coronavirus is SARS-CoV-2. In some aspects, the antibodies or antigen-binding fragments thereof are capable of neutralizing wild-type coronavirus in an in vitro infection assay, optionally wherein the coronavirus is SARS-CoV-2. In some aspects, the antibodies or antigen-binding fragments thereof are capable of neutralizing a coronavirus pseudovirus with spike protein in an in vitro infection assay, optionally wherein the coronavirus pseudovirus is a SARS-CoV-2 pseudovirus with a SARS-CoV-2 spike protein. [0047] In some aspects, the animal is a horse, a sheep, a goat, a camel, a cow, or a human. In some aspects, the animal is a horse. [0048] In some aspects, a method provided herein further comprises isolating the antibodies or antigen-binding fragments thereof from the animal to produce an isolated composition. In some aspects, a method provided herein further comprises isolating a gamma globulin (IgG) fraction from plasma of the animal to produce an isolated composition. [0049] In some aspects, a method provided herein further comprises solvent- and detergent-treating the isolated composition. In some aspects, the solvent and detergent treatment uses tri-n-butyl phosphate and Triton X-100. [0050] In some aspects, a method provided herein further comprises treating the isolated composition to reduce procoagulation activity. In some aspects, a method provided herein further comprises subjecting the isolated composition to virus filtration. In some aspects, a method provided herein further comprises subjecting the isolated composition to anion-exchange column chromatography. In some aspects, a method provided herein further comprises subjecting the isolated composition to cation-exchange chromatography. In some aspects, a method provided herein further comprises subjecting the isolated composition to pepsin digestion. In some aspects, a method provided herein further comprises processing the antibodies or antigen-binding fragments thereof to produce a composition comprising Fab, F(ab’)2 and/or F(ab’)2-related fragments. In some aspects, the composition comprising Fab, F(ab’)2 and/or F(ab’)2-related fragments comprises no more than 5% intact monomeric IgG antibodies. [0051] In some aspects, a composition provided herein comprises an antibody or antigen- binding fragment thereof produced any method provided herein. [0052] In some aspects, a pharmaceutical composition provided herein comprises an antibody or antigen-binding fragment thereof produced by any method provided herein and a pharmaceutically acceptable excipient. [0053] In some aspects, a composition provided herein comprises a mixture of antibodies or antigen-binding fragments thereof produced by any method provided herein. [0054] In some aspects, a pharmaceutical composition provided herein comprises a mixture of antibodies or antigen-binding fragments thereof produced by any method provided herein and a pharmaceutically acceptable excipient. [0055] In some aspects of a composition provided herein, the antibodies or antigen- binding fragments thereof in the composition comprises an increased percentage of antibodies or antigen-binding fragments that bind to the pre-fusion conformation of a coronavirus spike protein as compared to a mixture of antibodies or antigen-binding fragments produced using a wild-type coronavirus spike protein or fragment thereof. [0056] In some aspects, a composition provided herein comprises a mixture of antibodies or antigen-binding fragments thereof that bind to any protein, trimer, nanoparticle, or composition provided herein, wherein the composition comprises an increased percentage of antibodies or antigen-binding fragments that bind to the pre-fusion conformation of a coronavirus spike protein as compared to a mixture of antibodies or antigen-binding fragments produced using a wild-type coronavirus spike protein or fragment thereof. [0057] In some aspects, a pharmaceutical composition provided herein comprises (i) a mixture of antibodies or antigen-binding fragments thereof that bind to any protein, trimer, nanoparticle, or composition provided herein, wherein the composition comprises an increased percentage of antibodies or antigen-binding fragments that bind to the pre- fusion conformation of a coronavirus spike protein as compared to a mixture of antibodies or antigen-binding fragments produced using a wild-type coronavirus spike protein or fragment thereof and (ii) a pharmaceutically acceptable excipient. [0058] In some aspects of a composition provided herein, the mixture of antibodies or antigen-binding fragments thereof comprises equine antibodies or antigen-binding fragments thereof. In some aspects of a composition provided herein, the composition comprises Fab, F(ab’)2 and/or F(ab’)2-related fragments. In some aspects of a composition provided herein, the composition comprises a purified gamma globulin (IgG) fraction of equine plasma. In some aspects of a composition provided herein, the composition is a liquid. In some aspects of a composition provided herein, composition comprises about 100 mg protein /mL or about 50 mg protein /mL. In some aspects of a composition provided herein, the composition comprises about 2 to about 20 % antibodies or antigen-binding fragments thereof by weight. In some aspects of a composition provided herein, the composition further comprising a stabilizing agent. In some aspects of a composition provided herein, the composition has a pH of about 4 to about 6, about 5.5 to about 6, or about 5.7. In some aspects of a composition provided herein, the composition is a filtered sterile solution. [0059] In some aspects of a method of treating or preventing a coronavirus infection in a subject provided herein comprises administering to the subject any composition provided herein. In some aspects, the coronavirus infection is a SARS-CoV-2 infection. [0060] In some aspects, the composition is administered intravenously. In some aspects, the composition is administered intramuscularly. In some aspects, the composition is only administered once. In some aspects, the composition is administered at least twice. In some aspects, the administration increases the anti-coronavirus antibodies or antigen- binding fragments thereof in the subject by at least 2-fold, by at least 3-fold, by at least 4- fold, or by at least 5-fold. In some aspects, the administration increases the subject’s immunity to coronavirus. In some aspects, the administration promotes clearance of coronavirus, optionally wherein the coronavirus is SARS-CoV-2. In some aspects, the administration decreases the severity of a symptom of coronavirus infection. In some aspects, the subject is human. In some aspects, the subject is hospitalized BRIEF DESCRIPTION OF THE FIGURES [0061] FIG.1 provides a schematic a SARS-CoV-2 spike protein and H. pylori ferritin fusion protein (left) and a depiction of a nanoparticle comprising the same (right). Mutations in the SARS-CoV-2 spike protein (R685A, K986P, and V987P) and the H. pylori ferritin protein (N19Q) are denoted (See Example 1.) [0062] FIG.2 shows Western Blots using an anti-SARS CoV-1 spike antibody to detect expression of the SARS-CoV-2 spike protein: H. pylori ferritin fusion protein in Expi293 cells. Fractions of the cells were collected and analyzed by SDS-PAGE under reducing conditions prior to the Western blotting. (See Example 1.) [0063] FIG.3 shows Western Blots using a polyclonal ferritin antiserum to detect expression of the SARS-CoV-2 spike protein: H. pylori ferritin fusion protein in Expi293 cells (upper blots) and 293F cells (lower blots). Anion exchange chromatography (AEX) fractions of the cells were separated by native PAGE prior to the Western blotting. (See Example 1.) [0064] FIG.4 shows Western Blots using a polyclonal anti-ferritin serum to detect expression of the SARS-CoV-2 spike protein: H. pylori ferritin fusion protein in 293F cells. Material produced in 293F cells was pooled after AEX on the basis of immunoreactivity, concentrated, fractionated, and analyzed by native PAGE prior to the Western blotting. (See Example 1.) [0065] FIG.5 shows transmission electron microscopy (TEM) images of nanoparticles expressed in 293F cells in pooled SEC fractions after AEX. (See Example 2.) [0066] FIG.6 shows Western Blots using a polyclonal anti-ferritin serum (left) and a recombinant human ACE2 (right) to detect SARS-CoV-2 spike protein: H. pylori ferritin fusion protein nanoparticles produced in Expi293 cells. (See Example 2.) [0067] FIG.7 shows bio-layer interferometry results detecting the binding of nanoparticles to immobilized ACE2. (See Example 2.) [0068] FIG.8 (A-I) shows the reactivity of IgG in horse serum to SARS-CoV-2 spike protein after nanoparticles were administered to horses. (See Example 3.) Figures 8A, 8B, and 8C show results for horse# COVI906. Figures 8D, 8E, and 8F show results for horse# COVI906. Figures 8G, 8H, and 8I show results for horse# COVI906. (See Example 3.) [0069] FIG.9 shows the ability of serum from vaccinated horses to neutralize a pseudovirus bearing the SARS-CoV-2 spike protein. (See Example 4.) DETAILED DESCRIPTION [0070] The present disclosure provides proteins comprising modified coronavirus (e.g., SARS-CoV-2) spike polypeptides. The polypeptides can be expressed as fusion proteins with ferritin, which allows the fusion proteins to self-assemble into nanoparticles. The nanoparticles containing the fusion proteins can be administered to an animal (e.g., a horse or human) to generate an immune response (e.g., antibodies and antigen-binding fragments thereof) that are capable of neutralizing the coronavirus (e.g., SARS-CoV-2). The antibodies and antigen-binding fragments thereof (e.g., human or equine antibodies or antigen-binding fragments thereof) can be used to treat or prevent SARS-CoV-2 infection and/or COVID-19. The modified coronavirus spike polypeptides can be used as a vaccine in animals, including humans. Definitions [0071] A “coronavirus” is any of a large family (Coronaviridae) of single-stranded RNA viruses that have a lipid envelope with spike proteins. Exemplary coronaviruses include, e.g., severe acute respiratory syndrome (SARS, SARS-CoV, or SARS-CoV-1), Middle East respiratory syndrome (MERS), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). [0072] A “wild-type” coronavirus refers to a naturally occurring coronavirus. A “pseudovirus” is a chimeric virus which contains and expresses viral proteins of non- coronavirus origin and also contains and expressed the membrane/envelope proteins of a coronavirus virus, where the coronavirus membrane/envelope proteins mediate viral entry. However, a “pseudovirus” may not always induce pathogenesis as its wild-type counterpart does. Typically, a pseudovirus will have the membrane/envelope of a different virus replaced with the membrane/envelope of a coronavirus, thereby creating a chimeric virus. [0073] As used herein, the term “coronavirus disease-19” (“COVID-19”) refers to an infection with the SARS-CoV-2 virus. [0074] “Coronavirus spike protein,” “coronavirus spike polypeptide,” “coronavirus spike glycoprotein,” “coronavirus S protein,” “coronavirus S polypeptide, and “coronavirus S glycoprotein” are used interchangeable herein to refer to any coronavirus spike protein or coronavirus spike protein-encoding polynucleotide. The terms encompass “full-length,” unprocessed coronavirus spike protein as well as any forms of coronavirus spike protein that result from processing within a cell. The terms encompass naturally occurring variants of coronavirus spike protein, e.g., those encoded by splice variants, allelic variants, and strain variants as well as “modified” spike proteins. In some aspects, a “coronavirus spike protein” is a naturally occurring coronavirus spike protein. In some aspects, a “coronavirus spike protein” is a modified coronavirus spike protein. As used herein, the term “Wuhan_Hu-1 SARS-CoV-2 spike protein” refers to a mature protein comprising amino acids 16-1,273 of SEQ ID NO:5 (the full amino acid sequence as set forth in SEQ ID NO:5 includes the leader sequence of amino acids 1-15). [0075] “Ferritin protein” and “ferritin polypeptide,” are used interchangeable herein to refer to any ferritin protein or ferritin protein-encoding polynucleotide. The terms encompass “full-length,” unprocessed ferritin as well as any forms of ferritin protein that result from processing within a cell. The terms encompass naturally occurring variants of ferritin protein, e.g., those encoded by splice variants, allelic variants, and strain variants as well as “modified” ferritin proteins. In some aspects, a “ferritin protein” is a naturally occurring ferritin protein. In some aspects, a “ferritin protein” is a modified ferritin protein. [0076] As used herein “modified” protein is a protein that is similar to (i.e., maintains certain functions of) a specified naturally occurring protein but does not contain the exact full length amino acid sequence of the naturally occurring specified protein. A modified protein can contain e.g., an insertion(s), deletion(s) (e.g., truncation), and/or substitution(s) as compared to a naturally occurring protein. [0077] Accordingly, a “modified” coronavirus spike protein does not contain the exact full length amino acid sequence of any naturally occurring coronavirus spike protein. Similarly, a “modified” mature Wuhan Hu-1 SARS-CoV-2 spike protein does not contain amino acids 16-1273 of SEQ ID NO:5. However, in some aspects a “modified” SARS- CoV-2 spike protein or a “modified” Wuhan Hu-1 SARS-CoV-2 spike protein comprises an amino acid sequence that is at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to amino acids 16-1273 of SEQ ID NO:5. In some aspects a “modified” SARS-CoV-2 spike protein or a “modified” Wuhan Hu-1 SARS-CoV-2 spike protein comprises an amino acid sequence that is at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to amino acids 16-1208 of SEQ ID NO:5. In some aspects, a “modified” SARS-CoV-2 spike protein or a “modified” Wuhan Hu-1 SARS-CoV-2 spike protein comprises an amino acid sequence with no more than 10, no more than 9, no more than 8, no more than 7, no more than 6, no more than 5, no more than 4, or no more than 3 mutations as compared to amino acids 16-1273 of SEQ ID NO:5. In some aspects, a “modified” SARS-CoV-2 spike protein or a “modified” Wuhan Hu-1 SARS-CoV-2 spike protein comprises an amino acid sequence with no more than 10, no more than 9, no more than 8, no more than 7, no more than 6, no more than 5, no more than 4, or no more than 3 mutations as compared to amino acids 16-1208 of SEQ ID NO:5. In some aspects, a “modified” coronavirus spike protein (e.g., a modified SARS-CoV-2 spike protein) can bind to ACE2. In some aspects, a “modified” coronavirus spike protein (e.g., a modified SARS-CoV-2 spike protein) can assemble into a trimer. In some aspects, a “modified” coronavirus spike protein (e.g., a modified SARS-CoV-2 spike protein) can bind to ACE2 and can assemble into a trimer. In some aspects, a “modified” coronavirus spike protein (e.g., a modified SARS-CoV-2 spike protein) can bind to ACE2, can assemble into a trimer, and comprises an amino acid sequence that is at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to amino acids 16-1273 of SEQ ID NO:5. In some aspects, a “modified” coronavirus spike protein (e.g., a modified SARS-CoV-2 spike protein) can bind to ACE2, can assemble into a trimer, and comprises an amino acid sequence that is at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to amino acids 16-1208 of SEQ ID NO:5. In some aspects, a “modified” coronavirus spike protein (e.g., a modified SARS-CoV-2 spike protein) can bind to ACE2, can assemble into a trimer, and comprises an amino acid sequence with no more than 10, no more than 9, no more than 8, no more than 7, no more than 6, no more than 5, no more than 4, or no more than 3 mutations as compared to amino acids 16-1273 of SEQ ID NO:5. In some aspects, a “modified” coronavirus spike protein (e.g., a modified SARS- CoV-2 spike protein) can bind to ACE2, can assemble into a trimer, and comprises an amino acid sequence with no more than 10, no more than 9, no more than 8, no more than 7, no more than 6, no more than 5, no more than 4, or no more than 3 mutations as compared to amino acids 16-1208 of SEQ ID NO:5. In some aspects, a “modified” coronavirus spike protein (e.g., a modified SARS-CoV-2 spike protein) comprises an S1 subunit. In some aspects, a “modified” coronavirus spike protein (e.g., a modified SARS- CoV-2 spike protein) comprises an S2 subunit. In some aspects, a “modified” coronavirus spike protein (e.g., a modified SARS-CoV-2 spike protein) comprises an S1 subunit and an S2 subunit. [0078] Similarly, a “modified” ferritin protein does not contain the exact full length amino acid sequence of any naturally occurring ferritin protein, such as the amino acid sequence of SEQ ID NO:7. However, in some aspects a “modified” ferritin protein or fragment thereof comprises an amino acid sequence that is at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to SEQ ID NO:7. In some aspects a “modified” ferritin protein comprises an amino acid sequence that is at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to amino acids 5-167 of SEQ ID NO:7. In some aspects, a “modified” ferritin protein comprises an amino acid sequence with no more than 10, no more than 9, no more than 8, no more than 7, no more than 6, no more than 5, no more than 4, or no more than 3 mutations as compared to SEQ ID NO:7. In some aspects, a “modified” ferritin protein comprises an amino acid sequence with no more than 10, no more than 9, no more than 8, no more than 7, no more than 6, no more than 5, no more than 4, or no more than 3 mutations as compared to amino acids 5-167 of SEQ ID NO:7. In some aspects, a “modified” ferritin protein can self-assemble into a globular/spherical form. In some aspects, a “modified” ferritin protein can self-assemble into a globular/spherical form and comprises an amino acid sequence that is at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to SEQ ID NO:7. In some aspects, a “modified” ferritin protein can self-assemble into a globular/spherical form and comprises an amino acid sequence that is at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to amino acids 5-167 of SEQ ID NO:7. In some aspects, a “modified” ferritin protein can self-assemble into a globular/spherical form and comprises an amino acid sequence with no more than 10, no more than 9, no more than 8, no more than 7, no more than 6, no more than 5, no more than 4, or no more than 3 mutations as compared to SEQ ID NO:7. In some aspects, a “modified” ferritin protein can self- assemble into a globular/spherical form and comprises an amino acid sequence with no more than 10, no more than 9, no more than 8, no more than 7, no more than 6, no more than 5, no more than 4, or no more than 3 mutations as compared to amino acids 5-167 of SEQ ID NO:7. [0079] “Percent identity” refers to the extent of identity between two sequences (e.g., amino acid sequences or nucleic acid sequences). Percent identity can be determined by aligning two sequences, introducing gaps to maximize identity between the sequences. Alignments can be generated using programs known in the art. For purposes herein, alignment of nucleotide sequences can be performed with the blastn program set at default parameters, and alignment of amino acid sequences can be performed with the blastp program set at default parameters (see National Center for Biotechnology Information (NCBI) on the worldwide web, ncbi.nlm.nih.gov). [0080] A “corresponding position” or “corresponding amino acid”, e.g., in a coronavirus (S) protein refers to position of the amino acid residue where at least two coronavirus (S) protein sequences are aligned. For instance, an amino acid that “corresponds” to amino acid R685 in SEQ ID NO:5 is an amino acid in a protein sequence that aligns with amino acid 685 in SEQ ID NO:5. [0081] As used herein a “mutation” refers to an alteration, e.g., in a polynucleotide or polypeptide sequence. Mutations include, for example, insertions, deletions (e.g., truncations), and/or substitutions. In some aspects, a mutation in a polynucleotide sequence results in a mutation (e.g., insertion, deletion, and/or substitution) in the polypeptide encoded by the polynucleotide. As used herein, a “conservative amino acid substitution” is one in which the amino acid residue is replaced with an amino acid residue having a similar side chain. Families of amino acid residues having side chains have been defined in the art. These families include amino acids with basic side chains (e.g., lysine, arginine, histidine), acidic side chains (e.g., aspartic acid, glutamic acid), uncharged polar side chains (e.g., glycine, asparagine, glutamine, serine, threonine, tyrosine, cysteine, tryptophan), nonpolar side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine), beta-branched side chains (e.g., threonine, valine, isoleucine) and aromatic side chains (e.g., tyrosine, phenylalanine, tryptophan, histidine). Non-conservative amino acid substitutions are also possible. [0082] As used herein a “mutation that reduces furin cleavage” in a modified spike polypeptide refers to a mutation that decreases the percentage of polypeptides that are cleaved by furin as compared to a polypeptide of amino acids 16-1273 of SEQ ID NO:5. A “mutation that eliminates furin cleavage” in a modified spike polypeptide refers to a mutation that entirely abolishes cleavage of the polypeptide by furin. Such mutations can increase the amount of the polypeptide in the pre-cleavage conformation and thereby confer a more homogenous and regular presentation of the modified spike polypeptide. [0083] As used herein a “mutation that stabilizes the pre-fusion conformation” in a modified spike polypeptide refers to a mutation that increases the percentage of trimers in a “prefusion” conformation) as compared to trimers comprising polypeptides of amino acids 16-1273 of SEQ ID NO:5. The conformation of coronavirus trimers can be determined using cryogenic electron microscopy (cryo-EM) as disclosed in D. Wrapp et al., Science 10.1126/science.abb2507 (2020), and Cai et al. bioRxiv 2020.05.16.099317 (2020) which is herein incorporated by reference in its entirety. [0084] Coronavirus spike polypeptides and modified coronavirus spike polypeptides can assemble into trimers. As used herein a “trimer” refers to a polymer comprising three monomers. A homo-trimer contains three identical monomers, whereas in a hetero- trimer, the three monomers are not all identical. [0085] As provided herein are “fusion proteins” or “fusion polypeptides” comprising coronavirus (e.g., SARS-CoV-2) spike polypeptides and modified coronavirus (e.g., SARS-CoV-2) spike polypeptides. Unless otherwise noted, a fusion protein is a recombinant protein comprising amino acid sequences from at least two unrelated proteins that have been joined together, e.g., via a peptide bond, to make a single protein. The unrelated amino acid sequences can be joined directly to each other or they can be joined using a linker sequence. As used herein, proteins are unrelated, if their amino acid sequences are not found joined together via a peptide bond in their natural environment (e.g., inside a cell or viral particle). For example, the amino acid sequences of bacterial proteins such as ferritin and the amino acid sequences of coronavirus spike (S) glycoproteins are not naturally found joined together via a peptide bond. [0086] Polypeptides in a fusion protein can be joined or linked, e.g., by an amino acid linker such as a “glycine-serine” polypeptide or linker. A “glycine-serine” polypeptide or linker refers to a polypeptide or linker that comprises glycine and serine amino acids. In some aspects, all of the amino acids in a glycine-serine polypeptide or linker are either glycine or serine. [0087] As used herein a “nanoparticle” refers to a particle formed from self-assembling, monomeric subunit proteins with a diameter of tens of nanometers. For example, monomeric ferritin proteins self-assemble into ferritin nanoparticles. [0088] Ferritin is a 17 kilo Dalton (kD) protein that self-assembles into a spherical 24- unit (e.g., 8 trimers) capsid with a hollow core. SEQ ID NO:7 is an example of an amino acid sequence from a naturally occurring ferritin protein. The N-and C-termini of each ferritin monomer are positioned on the outer and inner core of the capsid, respectively. Ferritin nanoparticles have been discussed, for example, in WO 2018/045308, WO 2016/109792, WO 2018/183969, and WO 2013/044203, each of which is herein incorporated by reference in its entirety. [0089] As used herein, the term “immunogenic” refers to the ability of a specific protein to elicit an immune response to the protein or fragment thereof. The immune response can also be active against a protein comprising an amino acid sequence having a high degree of identity (e.g., at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%) with the protein or a fragment thereof. [0090] An “immune response” to a protein or nanoparticle provided herein can refer to a humoral and/or cellular immune response. A humoral immune response is mediated by antibodies and/or antigen-binding fragments thereof, including e.g., IgA or IgG antibodies or antigen-binding fragments thereof. A cellular immune response is medicated by white blood cells such as T-lymphocytes. [0091] As used herein, immune responses or antibodies or antigen-binding fragments thereof are “neutralizing” if they decrease the ability of (i) a coronavirus (e.g., SARS- CoV-2) or (ii) pseudovirus displaying a coronavirus (e.g., SARS-CoV-2) spike protein, to enter the cytoplasm of a host cell and/or to express in the host cell a gene encoded in the coronavirus’ or pseudovirus’ genome (e.g., a viral, pseudoviral, or reporter gene). The ability of antibodies or antigen-binding fragments to “neutralize” a coronavirus (e.g., SARS-CoV-2) or pseudovirus can be assayed using the “PsVN” assay in Example 4 herein. [0092] The terms “immune globulin,” “immunoglobulin” and “antibody” refer to a protein that recognizes and specifically binds to a target, such as a protein, polypeptide, peptide, carbohydrate, polynucleotide, lipid, or combinations of the foregoing through at least one antigen recognition site within the variable region of the immunoglobulin molecule. As used herein, the terms “immune globulin” and “antibody” encompasses intact polyclonal immune globulins, human immune globulins, and any other modified immunoglobulin molecule so long as the immune globulins exhibit the desired biological activity. An immune globulin can be of any the classes: e.g., IgA, IgD, IgE, IgG, and IgM, or subclasses (isotypes) thereof (e.g., IgG1, IgG2, IgG3, IgG4, IgA1 and IgA2), based on the identity of their heavy-chain constant domains referred to as alpha, delta, epsilon, gamma, and mu, respectively. The different classes of immunoglobulins have different subunit structures and three-dimensional configurations. [0093] The term “monoclonal antibodies,” as used herein, refers to antibodies that are produced by a single clone of B-cells and bind to the same epitope. In contrast, the term “polyclonal antibodies” refers to a population of antibodies that are produced by different B-cells and bind to different epitopes of the same antigen (e.g., different epitopes of the spike protein of SARS-CoV-2). [0094] The term “mixture” as used herein refers to a combination of at least two different components, e.g., a mixture of antibodies refers to at least two unique antibodies. The antibodies can differ e.g., based on their sequence, the target to which they bind, and/or the epitope to which they bind within the target. [0095] The term “antibody fragment” or “immune globulin fragment” refers to a portion of an intact antibody. An “antigen-binding fragment,” “antigen-binding domain,” or “antigen-binding region,” refers to a portion of an intact antibody that binds to an antigen. An antigen-binding fragment can contain the antigenic determining regions of an intact antibody or immune globulin (e.g., the complementarity determining regions (CDR)). Examples of antigen-binding fragments of antibodies include, but are not limited to Fab, Fab', F(ab')2, and Fv fragments, linear antibodies, and single chain antibodies. An antigen-binding fragment of an antibody can be derived from any animal species, such as horses and humans, or can be artificially produced. [0096] As used herein, the terms “variable region” or “variable domain” are used interchangeably and are common in the art. The variable region typically refers to a portion of an antibody, generally, a portion of a light or heavy chain, typically about the amino-terminal 110 to 120 amino acids or 110 to 125 amino acids in the mature heavy chain and about 90 to 115 amino acids in the mature light chain, which differ extensively in sequence among antibodies and are used in the binding and specificity of a particular antibody for its particular antigen. The variability in sequence is concentrated in those regions called complementarity determining regions (CDRs) while the more highly conserved regions in the variable domain are called framework regions (FR). Without wishing to be bound by any particular mechanism or theory, it is believed that the CDRs of the light and heavy chains are primarily responsible for the interaction and specificity of the antibody with antigen. [0097] The terms “VL” and “VL domain” are used interchangeably to refer to the light chain variable region of an antibody. [0098] The terms “VH” and “VH domain” are used interchangeably to refer to the heavy chain variable region of an antibody. [0099] As used herein, the term “constant region” or “constant domain” are interchangeable and have its meaning common in the art. The constant region is an antibody portion, e.g., a carboxyl terminal portion of a light and/or heavy chain which is not directly involved in binding of an antibody to antigen but which can exhibit various effector functions, such as interaction with the Fc receptor. The constant region of an immunoglobulin molecule generally has a more conserved amino acid sequence relative to an immunoglobulin variable domain. [0100] As used herein, the term “heavy chain” when used in reference to an antibody can refer to any distinct type, e.g., alpha (α), delta (δ), epsilon (ε), gamma (γ), and mu (µ), based on the amino acid sequence of the constant domain, which give rise to IgA, IgD, IgE, IgG, and IgM classes of antibodies, respectively, including subclasses of IgG, e.g., IgG₁, IgG₂, IgG₃, and IgG₄. Heavy chain amino acid sequences are well known in the art. [0101] As used herein, the term “light chain” when used in reference to an antibody can refer to any distinct type, e.g., kappa (κ) or lambda (λ) based on the amino acid sequence of the constant domains. Light chain amino acid sequences are well known in the art. [0102] As used herein, the terms “immunospecifically binds,” “immunospecifically recognizes,” “specifically binds,” and “specifically recognizes” are analogous terms in the context of antibodies or antigen-binding fragments thereof. These terms indicate that the antibody or antigen-binding fragment thereof binds to an epitope via its antigen-binding domain and that the binding entails some complementarity between the antigen binding domain and the epitope. Accordingly, for example, an antibody that “specifically binds” a coronavirus spike protein may be able to bind to one or more of SARS-CoV, MERS, and/or SARS-CoV-2 spike proteins, but the extent of binding to a virus not belonging to the family Coronaviridae’ is less than about 10% of the binding of the antibody to the coronavirus spike protein(s), e.g., as determined by bio-layer interferometry (BLI or “Octet”). Similarly, an antibody that “specifically binds” a modified coronavirus spike protein may also be able to bind a wild-type version of the coronavirus spike protein, but the binding to a virus not belonging to the family Coronaviridae’ is less than about 10% of the binding of the antibody to the coronavirus spike protein(s), e.g., by BLI. [0103] “Binding affinity” generally refers to the strength of the sum total of non-covalent interactions between a single binding site of a molecule (e.g., an immune globulin or antigen-binding fragment thereof) and its binding partner (e.g., an antigen). Unless indicated otherwise, as used herein, “binding affinity” refers to intrinsic binding affinity which reflects a 1:1 interaction between members of a binding pair (e.g., immune globulin or antigen-binding fragment thereof and antigen). The affinity of a molecule X for its partner Y can generally be represented by the dissociation constant (K_D). Affinity can be measured and/or expressed in a number of ways known in the art, including, but not limited to, equilibrium dissociation constant (KD), and equilibrium association constant (K_A). The K_D is calculated from the quotient of k_off/k_on, whereas K_A is calculated from the quotient of k_on/k_off. k_on refers to the association rate constant of, e.g., an immune globulin or antigen-binding fragment thereof to an antigen, and koff refers to the dissociation of, e.g., an immune globulin or antigen-binding fragment thereof from an antigen. The k_on and k_off can be determined by techniques known to one of ordinary skill in the art, such as BIAcore^® or KinExA. [0104] A polypeptide, antibody, polynucleotide, vector, cell, or composition which is "isolated" is a polypeptide, antibody, polynucleotide, vector, cell, or composition which is in a form not found in nature. Isolated polypeptides, antibodies, polynucleotides, vectors, cells, or compositions include those which have been purified to a degree that they are no longer in a form in which they are found in nature. In some aspects provided herein, an antibody, polynucleotide, vector, cell, or composition which is isolated is substantially pure. As used herein, "substantially pure" refers to material which is at least 50% pure (i.e., free from contaminants), at least 90% pure, at least 95% pure, at least 98% pure, or at least 99% pure. [0105] The terms "polypeptide," "peptide," and "protein" are used interchangeably herein to refer to polymers of amino acids of any length. The polymer can be linear or branched, it can comprise modified amino acids, and it can be interrupted by non-amino acids. The terms also encompass an amino acid polymer that has been modified naturally or by intervention; for example, disulfide bond formation, glycosylation, lipidation, acetylation, phosphorylation, or any other manipulation or modification, such as conjugation with a labeling component. Also included within the definition are, for example, polypeptides containing one or more analogs of an amino acid (including, for example, unnatural amino acids, etc.), as well as other modifications known in the art. [0106] As used herein, the term “host cell” can be any type of cell, e.g., a primary cell, a cell in culture, or a cell from a cell line. In some aspects, the term “host cell” refers to a cell transfected with a nucleic acid molecule and the progeny or potential progeny of such a cell. Progeny of such a cell may not be identical to the parent cell transfected with the nucleic acid molecule, e.g., due to mutations or environmental influences that may occur in succeeding generations or integration of the nucleic acid molecule into the host cell genome. [0107] The term "pharmaceutical formulation" refers to a preparation which is in such form as to permit the biological activity of the active ingredient to be effective, and which contains no additional components which are unacceptably toxic to a subject to which the formulation would be administered. The formulation can be sterile. [0108] As used herein, the terms “treatment,” “treating,” and the like, refer to obtaining a desired therapeutic pharmacologic and/or physiologic effect, i.e., the effect partially or completely cures an infection and/or adverse symptom attributable to the infection. In one aspect, the therapeutic effect is preventing an increase in severity of an infection and/or adverse symptom attributable to the infection. [0109] A “therapeutically effective amount” refers to an amount effective, at dosages and for periods of time necessary, to achieve a desired therapeutic result (e.g., treatment of an infection). [0110] A “prophylactically effective amount” refers to an amount effective, at dosages and for periods of time necessary, to achieve a desired prophylactic result (e.g., prevention of infection or disease onset). [0111] “Decrease” or “reduce” refers to a decrease or a reduction in a particular value of at least 5%, for example, a 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or 100% decrease as compared to a reference value. [0112] “Increase” refers to an increase in a particular value of at least 5%, for example, a 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, 100%, 200%, 300%, 400%, 500%, or more increase as compared to a reference value. [0113] A “vaccine” refers to a pharmaceutical composition that elicits a prophylactic or therapeutic immune response in a subject. In some cases, the immune response is a protective immune response. Typically, a vaccine elicits an antigen-specific immune response to an antigen of a pathogen, for example a viral pathogen, or to a cellular constituent correlated with a pathological condition. A vaccine can include a polynucleotide (such as a nucleic acid encoding a disclosed antigen), a polypeptide (such as a disclosed antigen), a virus, a cell, or one or more cellular constituents. In some aspects provided herein, vaccines, vaccine immunogens, vaccine compositions are expressed from fusion constructs and self-assembled into nanoparticles displaying an immunogen polypeptide (e.g., a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide) on the surface. [0114] As used herein the term “adjuvant” refers to a substance that enhances a subject’s immune response to an antigen, e.g., a coronavirus (e.g., SARS-CoV-2) spike polypeptide, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide, a trimer thereof, or a nanoparticle comprising a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide. [0115] The terms “administer,” “administering,” “administration,” and the like, as used herein, refer to methods that can be used to enable delivery of a composition (e.g., a therapeutic or prophylactic composition comprising a mixture of anti-SARS-CoV-2 antibodies and/or antigen-binding fragments thereof) to the desired site of biological action (e.g., intravenous administration). Administration techniques that can be employed with the agents and methods described herein are found in e.g., Goodman and Gilman, The Pharmacological Basis of Therapeutics, current edition, Pergamon; and Remington’s, Pharmaceutical Sciences, current edition, Mack Publishing Co., Easton, Pa. [0116] As used herein, the terms “subject” and “patient” are used interchangeably. The subject can be an animal. In some aspects, the subject is a mammal such as a non-human animal (e.g., cow, pig, horse, cat, dog, rat, mouse, monkey, or other primate, etc.). In some aspects, the subject is a horse. In some aspects, the subject is a human. [0117] The terms “exposed,” “exposure,” and the like refer to a subject that has come into contact with a person or animal that is known to be infected with a coronavirus (e.g., SARS-CoV-2). [0118] As used in the present disclosure and claims, the singular forms "a," "an," and "the" include plural forms unless the context clearly dictates otherwise. [0119] It is understood that wherever aspects are described herein with the language “comprising,” otherwise analogous aspects described in terms of “consisting of” and/or “consisting essentially of” are also provided. In this disclosure, "comprises," "comprising," "containing" and "having" and the like can mean "includes," "including," and the like; "consisting essentially of" or "consists essentially" are open-ended, allowing for the presence of more than that which is recited so long as basic or novel characteristics of that which is recited is not changed by the presence of more than that which is recited, but excludes prior art aspects. [0120] Unless specifically stated or obvious from context, as used herein, the term "or" is understood to be inclusive. The term "and/or" as used in a phrase such as "A and/or B" herein is intended to include both "A and B," "A or B," "A," and "B." Likewise, the term "and/or" as used in a phrase such as "A, B, and/or C" is intended to encompass each of the following aspects: A, B, and C; A, B, or C; A or C; A or B; B or C; A and C; A and B; B and C; A (alone); B (alone); and C (alone). [0121] As used herein, the terms “about” and “approximately,” when used to modify a numeric value or numeric range, indicate that deviations of up to 10% above and down to 10% below the value or range remain within the intended meaning of the recited value or range. It is understood that wherever aspects are described herein with the language “about” or “approximately” a numeric value or range, otherwise analogous aspects referring to the specific numeric value or range (without “about”) are also provided. [0122] Any polynucleotides, proteins, nanoparticles, compositions, and/or methods provided herein can be combined with one or more of any of the other polynucleotides, proteins, nanoparticles, compositions, and/or methods provided herein. Spike Polypeptides and Fragments Thereof [0123] Coronavirus entry into host cells is mediated by the transmembrane spike (S) glycoprotein (Walls et al., Cell 180:1-12 (2020)). The spike protein contains two functional subunits: the S1 and S2 subunits. The S1 subunit binds to the host cell receptor and contains the receptor binding domain (RBD), which recognizes the human receptor angiotensin converting enzyme 2 (ACE2). The S2 subunit fuses the viral and host cell membranes. The spike protein can be cleaved at the boundary between the S1 and S2 subunits, which can then remain non-covalently bound, e.g., in a “prefusion” conformation. A coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof can comprise amino acids 16-1273 of SEQ ID NO:5 or amino acids 16-1208 of SEQ ID NO:5. [0124] Modified coronavirus spike polypeptides and fragments thereof are provided herein. In some aspects, a modified coronavirus spike polypeptide or fragment thereof comprises a mutation, e.g., as compared to the amino acid sequence of a naturally occurring spike polypeptide. The modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof does not comprise amino acids 16-1,273 of SEQ ID NO:5. In some aspects, the modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof does not comprise amino acids 16-1,208 of SEQ ID NO:5. [0125] In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof comprises a mutation that reduces or eliminates furin cleavage. In some aspects, the mutation is in a furin cleavage site comprising the amino acid sequence of amino acids 682-685 of SEQ ID NO:5. In some aspects, the mutation that reduces or eliminates furin cleavage is an amino acid substitution. In some aspects, the mutation that reduces or eliminates furin cleavage comprises a mutation (e.g., substitution) of the amino acid corresponding to R685 in SEQ ID NO:5. In some aspects, the amino acid corresponding to R685 in SEQ ID NO:5 is substituted with an alanine (A). In some aspects, the mutation that reduces or eliminates furin cleavage comprises GSAS (SEQ ID NO:10) at the furin cleavage site corresponding to amino acids 682-685 of SEQ ID NO:5. In some aspects, the mutation that reduces or eliminates furin cleavage does not comprise GSAS at the furin cleavage site corresponding to amino acids 682-685 of SEQ ID NO:5. In some aspects, the mutation that reduces or eliminates furin cleavage does comprises an amino acid deletion (e.g., amino acids RRAR corresponding to amino acids 682-685 of SEQ ID NO:5 are mutated to a single alanine (A)). In some aspects, the mutation that reduces or eliminates furin cleavage does not comprise an amino acid deletion. In some aspects, the mutation that reduces or eliminates furin cleavage does not comprise mutation of amino acids RRAR corresponding to amino acids 682-685 of SEQ ID NO:5 to a single alanine (A)). [0126] In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof comprises a mutation that stabilizes a pre-fusion conformation. In some aspects, the mutation that stabilizes a pre-fusion conformation comprises a mutation of the amino acid corresponding to K986 in SEQ ID NO:5. In some aspects, the amino acid corresponding to K986 in SEQ ID NO:5 is substituted with a proline (P). In some aspects, the mutation that stabilizes a pre-fusion conformation comprises a mutation of the amino acid corresponding to V987 in SEQ ID NO:5. In some aspects, the amino acid corresponding to V987 in SEQ ID NO:5 is substituted with a proline (P). In some aspects, the mutation that stabilizes a pre-fusion conformation comprises a mutation of the amino acid corresponding to K986 and the amino acid corresponding to V987 in SEQ ID NO:5. In some aspects, the mutation that stabilizes a pre-fusion conformation comprises a mutation of the amino acid corresponding to K986 in SEQ ID NO:5 to proline (P) and a mutation of the amino acid corresponding to V987 in SEQ ID NO:5 to proline (P). [0127] As provided herein, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof can maintain features of a naturally occurring coronavirus (e.g., SARS-CoV-2) spike polypeptide. In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is capable of binding to angiotensin-converting enzyme 2 (ACE2). In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is capable of forming trimers. In some aspects, a modified coronavirus spike protein (e.g., a modified SARS-CoV-2 spike protein) can bind to ACE2 and can assemble into a trimer. [0128] In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof comprises a heptad repeat. In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof comprises two heptad repeats. In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof lacks a transmembrane domain. In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof comprises 2 heptad repeats and lacks a transmembrane domains. [0129] In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof comprises an S1 subunit, an S2 subunit, or an S1 and an S2 subunit. In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof does not comprise amino acids 1209-1273 of SEQ ID NO:5. In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof does not comprise an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to amino acids 1209-1273 of SEQ ID NO:5. In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof does not comprise an amino acid sequence corresponding to amino acids 1209-1273 of SEQ ID NO:5. [0130] In some aspects, the modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is at least 500 amino acids in length, at least 750 amino acids in length, at least 1,000 amino acids in length, at least 1,100 amino acids in length, at least 1,150 amino acids in length, or at least 1,190 amino acids in length. In some aspects, the modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is about 500 to about 1,273 amino acids in length, about 750 to about 1,273 amino acids in length, about 1,000 to about 1,273 amino acids in length, about 1,100 to about 1,273 amino acids in length, about 1,150 to about 1,273 amino acids in length, or about 1,200 to about 1,273 amino acids in length. In some aspects, the modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is about 500 to about 1,210 amino acids in length, about 750 to about 1,210 amino acids in length, about 1,000 to about 1,210 amino acids in length, about 1,100 to about 1,210 amino acids in length, about 1,150 to about 1,210 amino acids in length, or about 1,200 to about 1,210 amino acids in length. In some aspects, the modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is about 500 to about 1,208 amino acids in length, about 750 to about 1,208 amino acids in length, about 1,000 to about 1,208 amino acids in length, about 1,100 to about 1,208 amino acids in length, about 1,150 to about 1,208 amino acids in length, or about 1,200 to about 1,208 amino acids in length. In some aspects, the modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is about 500 to about 1,195 amino acids in length, about 750 to about 1,195 amino acids in length, about 1,000 to about 1,195 amino acids in length, about 1,100 to about 1,195 amino acids in length, or about 1,150 to about 1,195 amino acids in length. In some aspects, the modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is about 500 to about 1,192 amino acids in length, about 750 to about 1,192 amino acids in length, about 1,000 to about 1,192 amino acids in length, about 1,100 to about 1,192 amino acids in length, or about 1,150 to about 1,192 amino acids in length. [0131] In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof comprises amino acids 16-1,208 of SEQ ID NO:2. In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof comprises the amino acid sequence of SEQ ID NO:2. [0132] In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is at least 90%, 95%, 96%, 97%, 98%, or 99% identical to amino acids 16-1,208 of SEQ ID NO:2, but does not comprise amino acids 16-1208 of SEQ ID NO:5. In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is at least 90%, 95%, 96%, 97%, 98%, or 99% identical to the amino acid sequence of SEQ ID NO:2, but does not comprise amino acids 1-1208 of SEQ ID NO:5. [0133] In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is at least 90%, 95%, 96%, 97%, 98%, or 99% identical to amino acids 16-1208 of SEQ ID NO:5. In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is at least 90%, 95%, 96%, 97%, 98%, or 99% identical to amino acids 1-1208 of SEQ ID NO:5. [0134] In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is at least 90%, 95%, 96%, 97%, 98%, or 99% identical to amino acids 1-1208 of SEQ ID NO:5 or to amino acids 16-1208 of SEQ ID NO:5 and is capable of binding to angiotensin-converting enzyme 2 (ACE2). In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is at least 90%, 95%, 96%, 97%, 98%, or 99% identical to amino acids 1-1208 of SEQ ID NO:5 or to amino acids 16-1208 of SEQ ID NO:5 and is capable of mediating cell membrane fusion. In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is at least 90%, 95%, 96%, 97%, 98%, or 99% identical to amino acids 1-1208 of SEQ ID NO:5 or to amino acids 16-1208 of SEQ ID NO:5, is capable of binding to ACE2, and is capable of mediating cell membrane fusion. [0135] In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof comprises about 2 to about 10, about 2 to about 8, about 2 to about 6, about 2 to about 5, about 2 to about 4, or about 2 to about 3 mutations as compared to amino acids 1-1208 of SEQ ID NO:5 or to amino acids 16-1208 of SEQ ID NO:5. In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof comprises about 2 to about 10, about 2 to about 8, about 2 to about 6, about 2 to about 5, about 2 to about 4, or about 2 to about 3 mutations as compared to amino acids 1-1208 of SEQ ID NO:5 or to amino acids 16-1208 of SEQ ID NO:5 and is capable of binding to angiotensin-converting enzyme 2 (ACE2). In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof comprises about 2 to about 10, about 2 to about 8, about 2 to about 6, about 2 to about 5, about 2 to about 4, or about 2 to about 3 mutations as compared to amino acids 1-1208 of SEQ ID NO:5 or to amino acids 16-1208 of SEQ ID NO:5 and is capable of mediating cell membrane fusion. In some aspects, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof comprises about 2 to about 10, about 2 to about 8, about 2 to about 6, about 2 to about 5, about 2 to about 4, or about 2 to about 3 mutations as compared to amino acids 1-1208 of SEQ ID NO:5 or to amino acids 16-1208 of SEQ ID NO:5, is capable of binding to ACE2, and is capable of mediating cell membrane fusion. In some aspects, the about 2 to about 10, about 2 to about 8, about 2 to about 6, about 2 to about 5, about 2 to about 4, or about 2 to about 3 mutations are amino acid substitutions. In some aspects, the about 2 to about 10, about 2 to about 8, about 2 to about 6, about 2 to about 5, about 2 to about 4, or about 2 to about 3 mutations comprise at least 2 non-conservative amino acid substitutions. In some aspects, the about 2 to about 10, about 2 to about 8, about 2 to about 6, about 2 to about 5, about 2 to about 4, or about 2 to about 3 mutations comprise at least 3 non-conservative amino acid substitutions. In some aspects, the about 2 to about 10, about 2 to about 8, about 2 to about 6, about 2 to about 5, about 2 to about 4, or about 2 to about 3 mutations comprise no more than 5 non-conservative amino acid substitutions. [0136] In some aspects, a modified coronavirus spike polypeptide or fragment thereof is at least 1000 amino acids in length, at least 1050 amino acids in length, at least 1100 amino acids in length, at least 1150 amino acids in length, at least 1175 amino acids in length, or at least 1190 amino acids in length. [0137] In some aspects, a modified coronavirus spike polypeptide or fragment thereof is no more than 1250 amino acids in length, no more than 1225 amino acids in length, or no more than 1210 amino acids in length. [0138] In some aspects, a modified coronavirus spike polypeptide or fragment thereof is 1000-1250 amino acids in length, 1050-1250 amino acids in length, 1100-1250 amino acids in length, 1150-1250 amino acids in length, 1175-1250 amino acids in length, or 1200-1250 amino acids in length. In some aspects, a modified coronavirus spike polypeptide or fragment thereof is 1000-1225 amino acids in length, 1050-1225 amino acids in length, 1100-1225 amino acids in length, 1150-1225 amino acids in length, 1175- 1225 amino acids in length, or 1200-1225 amino acids in length. In some aspects, a modified coronavirus spike polypeptide or fragment thereof is 1000-1210 amino acids in length, 1050-1210 amino acids in length, 1100-1210 amino acids in length, 1150-1210 amino acids in length, 1175-1210 amino acids in length, or 1200-1210 amino acids in length. In some aspects, a modified coronavirus spike polypeptide or fragment thereof is 1000-1195 amino acids in length, 1050-1195 amino acids in length, 1100-1195 amino acids in length, 1150-1195 amino acids in length, or 1175-1195 amino acids in length. In some aspects, a modified coronavirus spike polypeptide or fragment thereof is 1000-1192 amino acids in length, 1050-1192 amino acids in length, 1100-1195 amino acids in length, 1150-1192 amino acids in length, or 1175-1192 amino acids in length. [0139] In some aspects, a modified coronavirus spike polypeptide or fragment thereof is a recombinant polypeptide. In some aspects, a modified coronavirus spike polypeptide or fragment thereof is isolated. [0140] In some aspects, a modified coronavirus spike polypeptide or fragment thereof provided herein is capable of eliciting an immune response to the modified spike polypeptide and/or a wild-type spike polypeptide (e.g., a polypeptide comprising amino acids 16-1273 of SEQ ID NO:5) in a mammal (e.g., a horse and/or a human). The immune response can be an immune response capable of neutralizing a wild-type coronavirus (e.g., wild-type SARS-CoV-2) in an in vitro infection assay. The immune response can, for example, be neutralizing antibodies or antigen-binding fragments thereof or T-cells. Multimers Comprising Spike Polypeptides [0141] Naturally occurring coronavirus spike (S) polypeptides form trimers that protrude from the viral surface and mediate entry into host cells. The trimers contain N-linked glycans that are important for proper folding. As discussed above, the naturally-occurring trimers are able to adopt multiple conformations, and mutations in the spike polypeptides can stabilize a pre-fusion conformation. [0142] Accordingly, provided herein are trimers comprising a modified coronavirus spike polypeptide or fragment thereof. The trimer can be a homotrimer, comprising three identical monomeric units, or a heterotrimer, wherein the three monomeric units are not all identical. [0143] Also provided herein are compositions comprising multiple (e.g., at least 2 or at least 10) trimers comprising modified spike polypeptides or fragments thereof. In such compositions, at least 70%, at least 80%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% of the trimers can be in a pre-fusion conformation. In some aspects, a composition comprising multiple (e.g., at least 2 or at least 10) trimers comprising modified spike polypeptides or fragments thereof comprises more (e.g., at least 1.5 times or at least 2 times as many) trimers in a pre-fusion conformation than a composition comprising multiple (e.g., at least 2 or at least 10) trimers comprising wild- type spike polypeptides (e.g., spike polypeptides comprising amino acids 16-1273 of SEQ ID NO:5). [0144] In some aspects, a multimer (e.g., a trimer) comprising a modified spike polypeptide is capable of binding to ACE2. In some aspects, a multimer (e.g., a trimer) comprising a modified spike polypeptide comprises a central helical stalk. [0145] In some aspects, a multimer (e.g., a trimer) comprising a modified spike polypeptide is recombinant. In some aspects, a multimer (e.g., a trimer) comprising a modified spike polypeptide is isolated. [0146] In some aspects, a multimer (e.g., a trimer) provided herein is capable of eliciting an immune response to the multimer (e.g., a trimer), the modified spike polypeptide in the multimer (e.g., a trimer), and/or a wild-type spike polypeptide (e.g., a polypeptide comprising amino acids 16-1273 of SEQ ID NO:5) in a mammal (e.g., a horse and/or a human). The immune response can be an immune response capable of neutralizing a wild-type coronavirus (e.g., wild-type SARS-CoV-2) in an in vitro infection assay. The immune response can, for example, be neutralizing antibodies or antigen-binding fragments thereof or T-cells. Fusion Proteins Comprising Spike Polypeptides [0147] Also provided herein are fusion proteins comprising coronavirus (e.g., SARS- CoV-2) spike polypeptides and fragments thereof or modified coronavirus (e.g., SARS- CoV-2) spike polypeptides and fragments thereof. The coronavirus (e.g., SARS-CoV-2) spike polypeptides and fragments thereof and modified coronavirus (e.g., SARS-CoV-2) spike polypeptides and fragments thereof can be fused, for example, to a scaffold protein which allows for self-assembly. In some aspects, a coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof or a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof is fused to a ferritin polypeptide or fragment thereof. [0148] Ferritin is a globular/spherical protein found in animals, bacteria, and plants. It can act to control the rate and location of hydrated iron ions and proteins to form a mineralized core. The globular/spherical form of ferritin is made up of monomeric ferritin proteins, which can have, e.g., the amino acid sequence of SEQ ID NO:7. Each monomeric ferritin protein has the topology of a helix bundle which includes a four antiparallel helix motif, with a shorter helix (the c-terminal helix) lying perpendicular to the long axis of the 4-helix bundle. According to convention, the helices are labeled, A, B, C, D, and E from the N-terminus. The N-terminal sequence lies adjacent to the nanoparticle 3-fold axis and extends to the surface, while the E helics pack together at the four-fold axis with the C-terminus extending into the particle core. The consequence of this packing creates two pores on the nanoparticle surface. It is believed that one or both of these pores represent the point by which the hydrated iron diffuse into and out of the nanoparticle. Following production, these monomeric ferritin proteins self-assemble into the globular/spherical ferritin protein. Thus, the globular/spherical form of ferritin comprises 24 monomeric ferritin proteins and has a capsid-like structure. [0149] In some aspects, the ferritin polypeptide or fragment thereof is a Helicobacter pylori ferritin polypeptide or fragment thereof. [0150] In some aspects, the ferritin polypeptide or fragment thereof is capable of directing self-assembly of monomeric ferritin subunits into the globular/spherical form of the protein. [0151] In some aspects, the ferritin polypeptide or fragment thereof (e.g., H. pylori ferritin polypeptide or fragment thereof) comprises a mutation that removes a potential glycosylation site, e.g., a potential N-linked glycosylation site. The potential glycosylation site (e.g., N-linked glycosylation site) can be one that is glycosylated when the ferritin is expressed as a secreted protein in mammalian or yeast cells. In some aspects, the H. pylori ferritin polypeptide or fragment thereof comprises a mutation of the amino acid corresponding to N19 in SEQ ID NO:7. In some aspects, the amino acid corresponding to N19 in SEQ ID NO:7 is substituted with a glutamine (Q). [0152] In some aspects, the ferritin polypeptide or fragment thereof comprises an N- terminal truncation. In some aspects, the ferritin polypeptide or fragment thereof does not comprise amino acids 1-2, 1-3, or 1-4 of SEQ ID NO:7. [0153] In some aspects, the ferritin polypeptide or fragment thereof comprises the amino acid sequence of SEQ ID NO:3. In some aspects, the ferritin polypeptide or fragment thereof comprises an amino acid sequence that at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of SEQ ID NO:3. In some aspects, the ferritin polypeptide or fragment thereof does not comprise the amino acid sequence of SEQ ID NO:7. In some aspects, the ferritin polypeptide or fragment thereof does not comprise amino acids 5-167 of SEQ ID NO:7. [0154] In some aspects, the ferritin polypeptide or fragment thereof is at least 50 amino acids in length, at least 75 amino acids in length, at least 100 amino acids in length, at least 125 amino acids in length, or at least 150 amino acids in length. In some aspects, the ferritin polypeptide or fragment thereof is about 50 to about 167 amino acids in length, about 75 to about 167 amino acids in length, about 100 to about 167 amino acids in length, about 125 to about 167 amino acids in length, or about 150 to about 167 amino acids in length. In some aspects, the ferritin polypeptide or fragment thereof is about 50 to about 163 amino acids in length, about 75 to about 163 amino acids in length, about 100 to about 163 amino acids in length, about 125 to about 163 amino acids in length, or about 150 to about 163 amino acids in length. [0155] In a protein comprising a modified coronavirus spike polypeptide (e.g., a SARS- CoV-2 spike polypeptide) or fragment thereof and a ferritin polypeptide or fragment thereof, the modified coronavirus spike polypeptide or fragment thereof is C-terminal to the ferritin polypeptide or fragment thereof. [0156] The modified coronavirus spike polypeptide (e.g., a SARS-CoV-2 spike polypeptide) or fragment thereof and the ferritin polypeptide or fragment thereof can be fused directly (e.g., through a peptide bond) or can be connected via a linker (e.g., a peptide linker). A linker can be about 2 to about 10 amino acids in length. A linker can be about 2 to about 5 amino acids in length. A linker can be about 2 to about 4 amino acids in length. A linker can be about 2 to about 3 amino acids in length. A linker can comprise all or predominantly glycine and serine amino acids. A linker can be about 2 to about 10 amino acids in length, wherein all of the amino acids are glycine or serine. A linker can be about 2 to about 5 amino acids in length, wherein all of the amino acids are glycine or serine. A linker can be about 2 to about 4 amino acids in length, wherein all of the amino acids are glycine or serine. A linker can be about 2 to about 3 amino acids in length, wherein all of the amino acids are glycine or serine. In some aspects, a linker comprises the amino acid sequence of SEQ ID NO:4. In some aspects, a linker does not comprise the sequence SGG (SEQ ID NO:8). [0157] In some aspects, a fusion protein comprising a modified coronavirus spike polypeptide or fragment thereof and a ferritin polypeptide or fragment thereof is at least 1,000 amino acids in length, at least 1,100 amino acids in length, at least 1,150 amino acids in length, at least 1,200 amino acids in length, or at least 1,250 amino acids in length. In some aspects, the fusion protein comprising a modified coronavirus spike polypeptide or fragment thereof and a ferritin polypeptide or fragment thereof is about 1,000 to about 1,300 amino acids in length, about 1,100 to about 1,300 amino acids in length, about 1,150 to about 1,300 amino acids in length, about 1,200 to about 1,300 amino acids in length, or about 1,250 to about 1,300 amino acids in length. In some aspects, the fusion protein comprising a modified coronavirus spike polypeptide or fragment thereof and a ferritin polypeptide or fragment thereof is about 1,000 to about 1,273 amino acids in length, about 1,100 to about 1,273 amino acids in length, about 1,150 to about 1,273 amino acids in length, about 1,200 to about 1,273 amino acids in length, or about 1,250 to about 1,273 amino acids in length. In some aspects, the fusion protein comprising a modified coronavirus spike polypeptide or fragment thereof and a ferritin polypeptide or fragment thereof is about 1,000 to about 1,257 amino acids in length, about 1,100 to about 1,257 amino acids in length, about 1,150 to about 1,257 amino acids in length, about 1,200 to about 1,257 amino acids in length, or about 1,250 to about 1,257 amino acids in length. [0158] In some aspects, a fusion protein comprising a modified coronavirus spike polypeptide or fragment thereof and a ferritin polypeptide or fragment thereof comprises amino acids 16-1,376 of SEQ ID NO:6. In some aspects, a fusion protein comprising a modified coronavirus spike polypeptide or fragment thereof and a ferritin polypeptide or fragment thereof comprises an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to amino acids 16-1,376 of SEQ ID NO:6. [0159] In some aspects, a fusion protein comprises a modified coronavirus spike polypeptide or fragment thereof comprising an amino acid sequence that is at least 90% identical to amino acids 16-1,208 of SEQ ID NO:2 or to the amino acid sequence of SEQ ID NO:2 and a ferritin polypeptide or fragment thereof comprising an amino acid sequence that is at least 90% identical to the amino acid sequence of SEQ ID NO:3. In some aspects, a fusion protein comprises a modified coronavirus spike polypeptide or fragment thereof comprising an amino acid sequence that is at least 95% identical to amino acids 16-1,208 of SEQ ID NO:2 or to the amino acid sequence of SEQ ID NO:2 and a ferritin polypeptide or fragment thereof comprising an amino acid sequence that is at least 95% identical to the amino acid sequence of SEQ ID NO:3. In some aspects, a fusion protein comprises a modified coronavirus spike polypeptide or fragment thereof comprising an amino acid sequence that is at least 96% identical to amino acids 16-1,208 of SEQ ID NO:2 or to the amino acid sequence of SEQ ID NO:2 and a ferritin polypeptide or fragment thereof comprising an amino acid sequence that is at least 96% identical to the amino acid sequence of SEQ ID NO:3. In some aspects, a fusion protein comprises a modified coronavirus spike polypeptide or fragment thereof comprising an amino acid sequence that is at least 97% identical to amino acids 16-1,208 of SEQ ID NO:2 or to the amino acid sequence of SEQ ID NO:2 and a ferritin polypeptide or fragment thereof comprising an amino acid sequence that is at least 97% identical to the amino acid sequence of SEQ ID NO:3. In some aspects, a fusion protein comprises a modified coronavirus spike polypeptide or fragment thereof comprising an amino acid sequence that is at least 98% identical to amino acids 16-1,208 of SEQ ID NO:2 or to the amino acid sequence of SEQ ID NO:2 and a ferritin polypeptide or fragment thereof comprising an amino acid sequence that is at least 98% identical to the amino acid sequence of SEQ ID NO:3. In some aspects, a fusion protein comprises a modified coronavirus spike polypeptide or fragment thereof comprising an amino acid sequence that is at least 99% identical to amino acids 16-1,208 of SEQ ID NO:2 or to the amino acid sequence of SEQ ID NO:2 and a ferritin polypeptide or fragment thereof comprising an amino acid sequence that is at least 99% identical to the amino acid sequence of SEQ ID NO:3. In some aspects, the modified coronavirus spike polypeptide or fragment thereof and the ferritin polypeptide or fragment thereof are connected by a linker (e.g., a glycine-serine linker) that is about 2 to about 10, about 2 to about 5, or about 2 to about 3 amino acids in length. [0160] In some aspects, a fusion protein comprising a modified coronavirus spike polypeptide or fragment thereof does not comprise the amino acid sequence of SEQ ID NO:5 and/or does not comprise the amino acid sequence of SEQ ID NO:7. In some aspects, a fusion protein comprising a modified coronavirus spike polypeptide or fragment thereof does not comprise amino acids 16-1273 of SEQ ID NO:5 and/or does not comprise the amino acid sequence of SEQ ID NO:7. In some aspects, a fusion protein comprising a modified coronavirus spike polypeptide or fragment thereof does not comprise amino acids 1-1208 of SEQ ID NO:5 and/or 5-167 of SEQ ID NO:7. In some aspects, a fusion protein comprising a modified coronavirus spike polypeptide or fragment thereof does not comprise amino acids 16-1208 of SEQ ID NO:5 and/or 5-167 of SEQ ID NO:7. [0161] In some aspects, a protein comprising a modified coronavirus spike polypeptide (e.g., a SARS-CoV-2 spike polypeptide) or fragment thereof and a ferritin polypeptide or fragment thereof is capable of self-assembling into a nanoparticle. [0162] Also provided herein are trimers comprising three fusion proteins, each fusion protein comprising a modified coronavirus spike polypeptide (e.g., a SARS-CoV-2 spike polypeptide) or fragment thereof and a ferritin polypeptide or fragment thereof. [0163] Also provided herein are compositions comprising multiple (e.g., at least 2 or at least 10) trimers comprising three fusion proteins, each fusion protein comprising a modified coronavirus spike polypeptide (e.g., a SARS-CoV-2 spike polypeptide) or fragment thereof and a ferritin polypeptide or fragment thereof. In such compositions, at least 70%, at least 80%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% of the trimers can be in a pre-fusion conformation. In some aspects, a composition comprising multiple (e.g., at least 2 or at least 10) trimers comprising such fusion proteins comprises more (e.g., at least 1.5 times or at least 2 times as many) trimers in a pre-fusion conformation than a composition comprising multiple (e.g., at least 2 or at least 10) trimers comprising wild-type spike polypeptides (e.g., spike polypeptides comprising amino acids 16-1273 of SEQ ID NO:5). [0164] In some aspects, a fusion protein comprising a modified coronavirus spike polypeptide or fragment thereof and a ferritin polypeptide or fragment thereof is capable of binding to ACE2. [0165] In some aspects, a fusion protein comprising a modified coronavirus spike polypeptide or fragment thereof and a ferritin polypeptide or fragment thereof is a recombinant protein. In some aspects, a fusion protein comprising a modified coronavirus spike polypeptide and a ferritin polypeptide or fragment thereof is isolated. [0166] In some aspects, a fusion protein comprising a modified coronavirus spike polypeptide or fragment thereof and a ferritin polypeptide or fragment thereof provided herein is capable of eliciting an immune response to the fusion protein, the modified spike polypeptide in the fusion protein, and/or a wild-type spike polypeptide (e.g., a polypeptide comprising amino acids 16-1273 of SEQ ID NO:5) in a mammal (e.g., a horse and/or a human). The immune response can be an immune response capable of neutralizing a wild-type coronavirus (e.g., wild-type SARS-CoV-2) in an in vitro infection assay. The immune response can, for example, be neutralizing antibodies or antigen-binding fragments thereof or T-cells. Nanoparticles [0167] Also provided herein are nanoparticles comprising modified coronavirus spike polypeptides or fragments thereof. The nanoparticles can comprise fusion proteins comprising modified coronavirus spike polypeptides or fragments thereof and ferritin polypeptides or fragment thereof, e.g., the nanoparticle is a multimer of fusion proteins. In some aspects, the nanoparticles can self-assemble. [0168] Nanoparticles comprising fusion proteins comprising ferritin polypeptides or fragments thereof are discussed in, for example, WO 2013/044203, WO 2015/183969, WO 2016/109792 and WO 2018/045308, each of which is herein incorporated by reference in its entirety. [0169] The nanoparticles can comprise trimers comprising modified coronavirus spike polypeptides or fragments thereof. The nanoparticles can comprise trimers of fusion proteins comprising modified coronavirus spike polypeptides or fragments thereof and ferritin polypeptides or fragment thereof. In some aspects, the nanoparticle comprises about 24 subunits. In some aspects, the nanoparticles comprise about 8 trimers. In some aspects, the nanoparticle has octahedral symmetry. [0170] In some aspects, the nanoparticles display at least a portion of the modified coronavirus spike polypeptide or fragment thereof on their surface, e.g., as trimers. Thus, the trimer can be accessible to the immune system of an animal when the nanoparticle is administered to the animal, and the trimer can thus elicit an immune response. Exemplary methods of determining whether a nanoparticle contains an accessible modified coronavirus spike polypeptide or fragment thereof (e.g., the RBD of the modified coronavirus spike polypeptide or fragment thereof) are provided in Examples 1 and 2 herein and include, e.g., bio-layer interferometry. [0171] In some aspects, a nanoparticle provided herein has a hydrodynamic radius of about 20 to about 90 nanometers as measured by dynamic light scattering (DLS). In some aspects, a nanoparticle provided herein has a hydrodynamic radius of about 30 to about 90 nanometers as measured by DLS. In some aspects, a nanoparticle provided herein has a hydrodynamic radius of about 20 to about 60 nanometers as measured by DLS. In some aspects, a nanoparticle provided herein has a hydrodynamic radius of about 35 to about 50 nanometers as measured by DLS. [0172] In some aspects, a nanoparticle provided herein comprises a ferritin core that has a radius of about 10 to about 17 nanometers as measured by transmission electron microscopy (TEM). In some aspects, a nanoparticle provided herein comprises a ferritin core that has a radius of about 11 to about 17 nanometers as measured by TEM. In some aspects, a nanoparticle provided herein comprises a ferritin core that has a radius of about 11 to about 13 nanometers as measured by TEM. In some aspects, a nanoparticle provided herein comprises a ferritin core that has a radius of about 11.5 to about 12.5 nanometers as measured by TEM. In some aspects, a nanoparticle provided herein comprises a ferritin core that has a radius of about 12 nanometers as measured by TEM. [0173] Also provided herein are compositions comprising multiple (e.g., at least 2 or at least 10) nanoparticles. In such compositions, at least 70%, at least 80%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% of the trimers in the nanoparticles can be in a pre-fusion conformation. In some aspects, a composition comprising multiple (e.g., at least 2 or at least 10) nanoparticles comprises more (e.g., at least 1.5 times or at least 2 times as many) trimers in a pre-fusion conformation than a composition comprising multiple (e.g., at least 2 or at least 10) nanoparticles comprising wild-type spike polypeptides (e.g., spike polypeptides comprising amino acids 16-1273 of SEQ ID NO:5). [0174] In some aspects, a nanoparticle provided herein is capable of binding to ACE2. [0175] In some aspects, a nanoparticle provided herein is recombinant. In some aspects, a nanoparticle provided herein is isolated. [0176] In some aspects, a nanoparticle provided herein is capable of eliciting an immune response to the nanoparticle, the modified spike polypeptide in the nanoparticle, and/or a wild-type spike polypeptide (e.g., a polypeptide comprising amino acids 16-1273 of SEQ ID NO:5) in a mammal (e.g., a horse and/or a human). The immune response can be an immune response capable of neutralizing a wild-type coronavirus (e.g., wild-type SARS- CoV-2) in an in vitro infection assay. The immune response can, for example, be neutralizing antibodies or antigen-binding fragments thereof or T-cells. [0177] In some aspects, a nanoparticle provided herein was expressed in a 293 cell. In some aspects, a nanoparticle provided herein was expressed in a HEK293F (293F) cell. Compositions Comprising Modified Spike Polypeptides and Nanoparticles [0178] Provided herein are compositions comprising a modified coronavirus (e.g. SARS- CoV-2) spike polypeptide, a protein comprising a modified spike polypeptide, a multimer (e.g., trimer) comprising a protein comprising a modified spike polypeptide, and/or a nanoparticle provided herein having the desired degree of purity in a physiologically acceptable carrier, excipient or stabilizer (Remington’s Pharmaceutical Sciences (1990) Mack Publishing Co., Easton, PA). Acceptable carriers, excipients, or stabilizers are nontoxic to recipients at the dosages and concentrations employed. [0179] In some aspects, compositions, e.g., pharmaceutical compositions, comprising a modified coronavirus (e.g. SARS-CoV-2) spike polypeptide, a protein comprising a modified spike polypeptide, a multimer (e.g., trimer) comprising a protein comprising a modified spike polypeptide, and/or a nanoparticle provided herein are provided in formulations with a pharmaceutically acceptable carrier (see, e.g., Gennaro, Remington: The Science and Practice of Pharmacy with Facts and Comparisons: Drugfacts Plus, 20th ed. (2003); Ansel et al., Pharmaceutical Dosage Forms and Drug Delivery Systems, 7th ed., Lippencott Williams and Wilkins (2004); Kibbe et al., Handbook of Pharmaceutical Excipients, 3rd ed., Pharmaceutical Press (2000)). [0180] In some aspects, compositions comprising a modified coronavirus (e.g. SARS- CoV-2) spike polypeptide, a protein comprising a modified spike polypeptide, a multimer (e.g., trimer) comprising a protein comprising a modified spike polypeptide, and/or a nanoparticle provided herein are immunogenic compositions. [0181] In some aspects, compositions comprising a modified coronavirus (e.g. SARS- CoV-2) spike polypeptide, a protein comprising a modified spike polypeptide, a multimer (e.g., trimer) comprising a protein comprising a modified spike polypeptide, and/or a nanoparticle provided herein are vaccine compositions. [0182] Pharmaceutical compositions described herein can be useful in vaccinating a mammal, e.g., a horse. Pharmaceutical compositions described herein can be useful in eliciting an immune response, e.g., a neutralizing immune response, in a mammal, e.g., a horse. Pharmaceutical compositions described herein can be useful in producing an immune response, e.g., a neutralizing immune response, in a mammal, e.g., a horse, wherein the immune response (e.g. antibodies or antigen-binding fragments thereof) can be isolated and administered to a subject in need thereof. [0183] Pharmaceutical compositions described herein can be useful in producing antibodies or antigen-binding fragments thereof that specifically bind to a modified coronavirus (e.g. SARS-CoV-2) spike polypeptide and/or a wild-type modified coronavirus (e.g. SARS-CoV-2) spike polypeptide (e.g., a polypeptide comprising amino acids 16-1273 of SEQ ID NO:5). The antibodies or antigen-binding fragments thereof can be capable of neutralizing wild-type coronavirus (e.g., wild-type SARS-CoV-2) in an in vitro infection assay. The antibodies or antigen-binding fragments thereof can be capable of neutralizing a coronavirus pseudovirus (e.g., a SARS-CoV-2 pseudovirus) in an in vitro infection assay [0184] In some aspects, a composition comprises (i) a modified coronavirus (e.g. SARS- CoV-2) spike polypeptide, a protein comprising a modified spike polypeptide, a multimer (e.g., trimer) comprising a protein comprising a modified spike polypeptide, and/or a nanoparticle provided herein and (ii) an adjuvant. The adjuvant can be, for example, as CPG7909 and/or aluminum hydroxide. Polynucleotides and Methods of Producing Modified Spike Polypeptides, Fusion Proteins, Trimers, and Nanoparticles [0185] Also provided herein are polynucleotides comprising a nucleotide sequence encoding a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or a fragment thereof or a fusion protein thereof (e.g., a fusion protein comprising a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or a fragment thereof and a ferritin polypeptide or fragment thereof) and vectors, e.g., vectors comprising such polynucleotides for recombinant expression in host cells. [0186] In some aspects, a polynucleotide provided herein comprises a nucleotide sequence encoding amino acids 16-1,208 of SEQ ID NO:2 or the amino acid sequence of SEQ ID NO:2. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence encoding amino acids 16-1,208 of SEQ ID NO:2 or the amino acid sequence of SEQ ID NO:2 and a nucleotide sequence encoding the amino acid sequence of SEQ ID NO:3. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence encoding amino acids 16-1,208 of SEQ ID NO:2 or the amino acid sequence of SEQ ID NO:2 and the amino acid sequence of SEQ ID NO:3. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence encoding amino acids 16-1,376 of SEQ ID NO:6 or the amino acid sequence of SEQ ID NO:6. [0187] In some aspects, a polynucleotide provided herein comprises a nucleotide sequence comprising the sequence of SEQ ID NO:1. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence comprising nucleotides 905-5032 of SEQ ID NO:1. [0188] In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 80% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:2 or encodes amino acids 15- 1,208 of SEQ ID NO:2. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 80% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes (i) the amino acid sequence of SEQ ID NO:2 or amino acids 15-1,208 of SEQ ID NO:2 and (ii) SEQ ID NO:3. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 80% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:6 or amino acids 16-1,376 of SEQ of SEQ ID NO:6. [0189] In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 85% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:2 or encodes amino acids 15- 1,208 of SEQ ID NO:2. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 85% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes (i) the amino acid sequence of SEQ ID NO:2 or amino acids 15-1,208 of SEQ ID NO:2 and (ii) SEQ ID NO:3. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 85% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:6 or amino acids 16-1,376 of SEQ of SEQ ID NO:6. [0190] In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 90% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:2 or encodes amino acids 15- 1,208 of SEQ ID NO:2. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 90% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes (i) the amino acid sequence of SEQ ID NO:2 or amino acids 15-1,208 of SEQ ID NO:2 and (ii) SEQ ID NO:3. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 90% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:6 or amino acids 16-1,376 of SEQ of SEQ ID NO:6. [0191] In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 95% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:2 or encodes amino acids 15- 1,208 of SEQ ID NO:2. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 95% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes (i) the amino acid sequence of SEQ ID NO:2 or amino acids 15-1,208 of SEQ ID NO:2 and (ii) SEQ ID NO:3. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 95% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:6 or amino acids 16-1,376 of SEQ of SEQ ID NO:6. [0192] In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 96% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:2 or encodes amino acids 15- 1,208 of SEQ ID NO:2. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 96% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes (i) the amino acid sequence of SEQ ID NO:2 or amino acids 15-1,208 of SEQ ID NO:2 and (ii) SEQ ID NO:3. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 96% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:6 or amino acids 16-1,376 of SEQ of SEQ ID NO:6. [0193] In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 97% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:2 or encodes amino acids 15- 1,208 of SEQ ID NO:2. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 97% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes (i) the amino acid sequence of SEQ ID NO:2 or amino acids 15-1,208 of SEQ ID NO:2 and (ii) SEQ ID NO:3. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 97% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:6 or amino acids 16-1,376 of SEQ of SEQ ID NO:6. [0194] In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 98% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:2 or encodes amino acids 15- 1,208 of SEQ ID NO:2. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 98% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes (i) the amino acid sequence of SEQ ID NO:2 or amino acids 15-1,208 of SEQ ID NO:2 and (ii) SEQ ID NO:3. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 98% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:6 or amino acids 16-1,376 of SEQ of SEQ ID NO:6. [0195] In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 99% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:2 or encodes amino acids 15- 1,208 of SEQ ID NO:2. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 99% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes (i) the amino acid sequence of SEQ ID NO:2 or amino acids 15-1,208 of SEQ ID NO:2 and (ii) SEQ ID NO:3. In some aspects, a polynucleotide provided herein comprises a nucleotide sequence at least 99% identical to the sequence of SEQ ID NO:1, to nucleotides 905-5032 of SEQ ID NO:1, or to nucleotides 950-5032 of SEQ ID NO:1, wherein the nucleotide sequence encodes the amino acid sequence of SEQ ID NO:6 or amino acids 16-1,376 of SEQ of SEQ ID NO:6. [0196] Also provided herein are polynucleotides encoding a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or a fusion protein thereof that are optimized, e.g., by codon/RNA optimization, replacement with heterologous signal sequences, and/or elimination of mRNA instability elements. Methods to generate optimized nucleic acids encoding a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or a fusion protein thereof for recombinant expression by introducing codon changes (e.g., a codon change that encodes the same amino acid due to the degeneracy of the genetic code) and/or eliminating inhibitory regions in the mRNA can be carried out by adapting the optimization methods described in, e.g., U.S. Patent Nos.5,965,726; 6,174,666; 6,291,664; 6,414,132; and 6,794,498, accordingly. [0197] In some aspects, a polynucleotide provided herein is operably linked to a promoter. Operably linked means that a protein encoded by the linked polynucleotide can be expressed when the linked promoter is activated. A promoter can be, by way of example, a CMV promoter. In one aspect, a vector provided herein comprises a promoter, e.g., a CMV promoter, operably linked a polynucleotide encoding a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or a fragment thereof or a fusion protein thereof (e.g., a fusion protein comprising a modified coronavirus (e.g., SARS- CoV-2) spike polypeptide or a fragment thereof and a ferritin polypeptide or fragment thereof). [0198] Polynucleotides and vectors provided herein can be, e.g., in the form of RNA or in the form of DNA. DNA includes cDNA, genomic DNA, and synthetic DNA, and DNA can be double-stranded or single-stranded. If single stranded, DNA can be the coding strand or non-coding (anti-sense) strand. In some aspects, the polynucleotide is a cDNA or a DNA lacking one more endogenous introns. In some aspects, a polynucleotide is a non-naturally occurring polynucleotide. In some aspects, a polynucleotide is recombinantly produced. In some aspects, the polynucleotides are isolated. In some aspects, the polynucleotides are substantially pure. In some aspects, a polynucleotide is purified from natural components. [0199] In some aspects, provided herein are vectors (e.g., expression vectors) comprising polynucleotides comprising nucleotide sequences encoding a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or a fusion protein thereof for recombinant expression in host cells. In some aspects, a vector provided herein is a pcDNA3.1(-) expression vector. An expression vector can be transferred to a cell (e.g., host cell) by conventional techniques and the resulting cells can then be cultured by conventional techniques to produce a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or a fusion protein thereof. [0200] Accordingly, also provided herein are cells, e.g. host cells, comprising polynucleotides for recombinantly expressing a modified coronavirus (e.g., SARS-CoV- 2) spike polypeptide or a fusion protein thereof. Also provided herein are cells, e.g. host cells, comprising such vectors for recombinantly expressing a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or a fusion protein thereof. In a particular aspect, provided herein are methods for producing a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide, a fusion protein thereof, a trimer comprising such a modified spike polypeptide or fusion protein, or a nanoparticle comprising such a modified spike polypeptide or fusion protein, the methods comprising expressing modified coronavirus (e.g., SARS-CoV-2) spike polypeptide or a fusion protein thereof in a host cell. In some aspects, the host cell is a 293 cell. In some aspects, the host cell is a HEK293F (293F) cell. [0201] Once a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide, a fusion protein thereof, a trimer comprising such a modified spike polypeptide or fusion protein, or a nanoparticle comprising such a modified spike polypeptide or fusion protein described herein has been produced by recombinant expression, it can be purified by any method known in the art for purification of such a polypeptide, fusion protein, trimer, or nanoparticle, for example, by chromatography (e.g., ion exchange, affinity, particularly by affinity for the specific antigen after Protein A, and sizing column chromatography), centrifugation, differential solubility, tangential flow filtration, diafiltration, by any other standard technique for the purification of proteins, trimers, and/or nanoparticles, and/or any other technique for purification provided in Examples 1-2 herein. [0202] For instance, tangential flow filtration and/or diafiltration can be used, e.g., to concentrate nanoparticles (see e.g., Example 1 herein). [0203] In some aspects, nanoparticles are purified using at least one chromatography step. In some aspects, nanoparticles are purified using two or more chromatography steps. In some aspects, nanoparticles are purified using anion exchange chromatography. In some aspects, nanoparticles are purified using size exclusion chromatography. In some aspects, nanoparticles are purified using anion exchange chromatography and then size exclusion chromatography. [0204] Nanoparticles can be purified by binding to a sepharose resin, concentrating the resin, and performing anion exchange chromatography (AEX) (see e.g., Example 1 herein). [0205] Nanoparticles can also be purified by collecting size exclusion chromatography (SEC) fractions and pooling the fractions after anion exchange chromatography (AEX), e.g., on the basis of immunoreactivity as determined by native PAGE followed by Western blot (see e.g., Examples 1 and 2 herein). Uses of Modified Spike Polypeptides, Fusion Proteins, Trimers, and Nanoparticles [0206] As provided herein, a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide, a fusion protein thereof, a trimer comprising such a modified spike polypeptide or fusion protein, or a nanoparticle comprising such a modified spike polypeptide or fusion protein described herein can be used to vaccinate an animal, e.g., such that the animal produces an immune response against the polypeptide, fusion protein, trimer, or nanoparticle. The immune response can be a B-cell response, which results in the production of antibodies or antigen-binding fragments thereof against the polypeptide, fusion protein, trimer, or nanoparticle. In one aspect, the immune response comprises antibodies or antigen-binding fragments thereof that immunospecifically bind to the pre-fusion conformation of a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide. The immune response can be capable of neutralizing wild-type and/or pseudovirus coronavirus (e.g., SARS-CoV-2) in an in vitro infection assay. The animal can be, for example, a horse, a sheep, a goat, a camel, a cow, or a human. In some aspects, the animal is a horse. [0207] The immune response of an animal vaccinated with a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide, fusion protein, trimer, or nanoparticle are also provided herein can be isolated to produce an isolated composition. For example, antibodies or antigen-binding fragments thereof produced in response to a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide, fusion protein, trimer, or nanoparticle provided herein (e.g., a gamma globulin (IgG) fraction of a vaccinated animal’s plasma) can be isolated from the animal to produce an isolated composition. The isolated composition can be treated with a solvent and/or a detergent (e.g., using tri-n-butyl phosphate and/or Triton X-100), can be treated to reduce procoagulation activity, can be subject to viral filtration, can be subject to anion-exchange column chromatography and/or cation-exchange chromatography, and/or can be pepsin digested. [0208] Accordingly, compositions comprising antibodies or antigen-binding fragments thereof produced by an animal (e.g., a horse) in response to a modified coronavirus (e.g., SARS-CoV-2) spike polypeptide, fusion protein, trimer, or nanoparticle are also provided herein. Such a composition can be isolated. In some aspects, such a composition comprises an increased percentage of antibodies or antigen-binding fragments that bind to the pre-fusion conformation of a coronavirus spike polypeptide as compared to a mixture of antibodies or antigen-binding fragments produced using a wild-type coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof (e.g., by vaccinating an animal such a horse with a wild-type coronavirus (e.g., SARS-CoV-2) spike polypeptide or fragment thereof. Such composition can comprise polyclonal antibodies or antigen-binding fragments thereof. Accordingly, such compositions can comprise a mixture of antibodies or antigen-binding fragments thereof. In some aspects, such a composition comprises Fab, F(ab’)2 and/or F(ab’)2-related fragments. In some aspects, such a composition comprises a purified gamma globulin (IgG) fraction of plasma, e.g., equine plasma. In some aspects, such a composition is liquid. In some aspects, such a composition comprises about 100 mg protein /mL. In some aspects, such a composition is a filtered sterile solution. [0209] Such a composition can be administered to a subject, e.g., a human subject. The administration can be for the treatment or prevention of a coronavirus infection (e.g., a SARS-CoV-2 infection or COVID-19). The composition can be administered intravenously or intramuscularly. The composition can be administered repeatedly (e.g., at least twice) or as a single dose. The administration can increase the anti-coronavirus antibodies or antigen-binding fragments thereof (e.g., anti-SARS-CoV-2 antibodies or antigen-binding fragments thereof) in the subject by at least 2-fold, by at least 3-fold, by at least 4-fold, or by at least 5-fold. The administration can increase the patient’s immunity to coronavirus (e.g., to SARS-CoV-2), promote clearance of the coronavirus (e.g., SARS-CoV-2), and or decreases the severity of a symptom of coronavirus (e.g., SARS-CoV-2) infection. [0210] In some aspects, the subject is human. In some aspects, the subject is hospitalized. In some aspects, the subject is in an intensive care unit. Examples [0211] The examples in this Examples Section are offered by way of illustration, and not by way of limitation. Example 1: Design, expression, and purification of SARS-CoV-2 nanoparticles [0212] An expression plasmid was prepared (SEQ ID NO:1) containing the coding sequence for a modified SARS-CoV-2 spike protein amino acid sequence (SEQ ID NO:2; amino acids 16-1,208 of SEQ ID NO:2 correspond to the mature protein (lacking the leader sequence)) fused to a H. pylori ferritin amino acid sequence (SEQ ID NO:3) with an intervening amino acid linker (SEQ ID NO:4). In SEQ ID NO:1, the coding sequence for the SARS-CoV-2 spike is nucleotides 905-4528 and ferritin is 4538-5032. The plasmid of SEQ ID NO:1 was prepared from a 4128 base pair synthetic construct cloned into the pcDNA3.1(-) expression vector that uses a CMV promoter for expression in mammalian cells. The SARS-CoV-2 spike protein has 3 key mutations compared to the reference sequence QHD43416.1: R685A, K986P, and V987P. The R685A mutation is designed to reduce furin cleavage at the S1/S2 cleavage site to restrict the variability of conformations that the spike can adopt (Walls et al., Cell 180: 1-12 (2020), which is herein incorporated by reference in its entirety, discusses cleavage of the spike protein by furin). The K986P and V987P mutations are designed to stabilize the stem in a pre-fusion conformation (D. Wrapp et al., Science 10.1126/science.abb2507 (2020) and Pallesen et al., PNAS: E7348-E7357 (2017), each of which is herein incorporated by reference in its entirety). Additionally the SARS-CoV-2 spike protein sequence is truncated at residue Q1208, at which point a linker peptide GSG (SEQ ID NO:4) is inserted between the carboxy terminus of the SARS-CoV-2 spike and the amino terminus of H. pylori ferritin. The H. pylori ferritin scaffold corresponds to amino acids 5-167 of sequence WP_000949190.1 and contains an N19Q mutation (as numbered in the reference sequence) as well as a C-terminal SGS sequence (Figure 1). This N19Q mutation eliminates a potential glycosylation site to ensure that glycosylation does not disrupt nanoparticle formation, spike conformation, or accessibility of the spike to antibodies. [0213] Expression of the SARS-CoV-2 spike:ferritin fusion protein was achieved by transfecting HEK293F (hereafter referred to as 293F) cells or Expi293™ cells (both cell lines from Thermo Fisher Scientific) with the expression plasmid described above. 293F cells banked in CD293 medium were transfected using PEI Max from Polysciences without a medium exchange by splitting the cells 1:5 with Freestyle™ 293 medium and monitoring cell density so that it stayed below 3x10⁶ cells/mL. Cultures were then scaled up to 10 L using Freestyle 293 medium. Expi293 cells were transfected directly in Expi293 expression medium. [0214] The ferritin portion of the fusion protein enables the spontaneous assembly of a nanoparticle that incorporates 24 SARS-CoV-2 spike:ferritin monomers. The nature of nanoparticle assembly in this way is designed to allow for trimers of the SARS-CoV-2 spike to assemble at the vertex of every three monomers; eight such trimers are intended to occur on each nanoparticle (Figure 1). Each SARS-CoV-2 spike:ferritin monomer has a predicted molecular weight of 153 kDa, and each SARS-CoV-2 spike:ferritin nanoparticle has a predicted molecular weight of 3,672 kDa, or 3.7 MDa. The predicted isolelectric point (pI) is 5.88, and the predicted charge at neutral pH is -31.70. [0215] On day 5 post-transfection, cell culture medium was harvested and sterile filtered. Supernatants were diluted 1:3 with NanoPure™ water supplemented with 1M HEPES, pH 7.5. In some cases, tangential flow filtration and diafiltration were used to concentrate the filtered medium to one-tenth of the initial volume and buffer exchange into Q Sepharose® High Performance equilibration buffer. Ultimately, nanoparticles were batch-bound to Q Sepharose High Performance resin overnight at 2-8 °C while shaking. The resin was concentrated by removing the supernatant after settling and after applying the resin to a 0.45 µm filter. Anion exchange chromatography (AEX) was performed by running a linear gradient from 0-100% 20 mM HEPES, pH 7.5 + 1 M NaCl to elute nanoparticles from the resin. Fractions were collected and analyzed by SDS- PAGE under reducing conditions followed by Western blotting. Immunoreactivity was determined using a cross-reactive polyclonal rabbit anti-SARS CoV-1 spike antibody followed by probing with an anti-Rb IgG alkaline phosphatase antibody. Blots were developed using 5-bromo-4-chloro-3-indolyl-phosphate/nitro blue tetrazolium (BCIP/NBT) substrate. Expression of the construct in Expi293 cells was confirmed under these electrophoresis conditions (Figure 2), but this method was not sufficient to determine whether or not particles containing a multiplicity of monomers were forming. [0216] To better determine whether or not particles were forming, AEX fractions from expression in Expi293 were separated by native PAGE on a 3-12% precast gel. After electrophoresis, samples were transferred to a polyvinylidene difluoride (PVDF) membrane. Membranes were blocked with 3% bovine serum albumin (BSA) and probed with a rabbit polyclonal ferritin antiserum and detected with an anti-rabbit secondary conjugated to alkaline phosphatase. Blots were developed with an BCIP/NBT substrate. In Figure 3, the upper row of blots show the distribution of immunoreactive material produced in Expi293 cells fractionated by AEX. High molecular weight (MW) immunoreactive species were clearly visible throughout AEX fractionation. The exact MW could not be determined as there are no commercially available MW standards for proteins or nanoparticles of this size. The SARS-CoV-2 nanoparticles migrate behind the highest MW standard used in these assays (1236 kDa; NativeMark™ Unstained Protein Standard), so the retarded migration pattern and single high MW immunoreactive species indicate that nanoparticles are forming and migrating in accordance with the predicted MW of 3.7 MDa. Lower MW immunoreactive material was also present, possibly corresponding to partially assembled nanoparticles. Immunoreactivity of material to the ferritin antiserum in the AEX fractions demonstrates that a high MW protein species is produced in the expression cultures and demonstrates that the ferritin core of the nanoparticle is assembled. As a comparison, expressions in 293F cells were performed. AEX fractions from 293F expressions demonstrated a more homogeneous high MW species throughout the AEX fractionation (Figure 3, lower blots). Expression in 293F cells was judged to be superior to expression in Expi293 in terms of a lack of, or less, lower MW contaminants from 293F cells. [0217] Material produced in 293F cells was pooled after AEX on the basis of immunoreactivity as determined by native PAGE followed by Western blot. Pooled material was concentrated using 100 kDa spin filters prior to fractionation by size exclusion chromatography over HiLoad® Superdex® S-20026/60 columns. Fractions collected by size exclusion chromatography (SEC) were analyzed by native PAGE followed by native Western blotting as described above (Figure 4). In Figure 4, the image on the left displays representative results of native PAGE after AEX fractionation, and the image on the right shows the distribution of immunoreactive fractions. In some cases, fractions were pooled on the basis of demonstrable immunoreactivity after SEC. In other cases, dynamic light scattering (DLS) was also used to inform the pooling strategy. Final pools, in 1x PBS, were supplemented with 80 mg/mL sucrose and frozen at -80 °C. Example 2: Characterization of SARS-CoV-2 nanoparticle [0218] Transmission electron microscopy (TEM) was used to confirm the presence of nanoparticles expressed in 293F cells in pooled SEC fractions after AEX. Samples were diluted 1:3 with DH2O and adsorbed to glow discharged ultrathin carbon coated copper grids for 2 minutes. After a brief series of DH2O rinses, grids were negatively stained in 0.75% uranyl formate for 2 minutes, blotted with filter paper, and aspirated dry. Grids were viewed on a Hitachi H7600 TEM operating at 80 kV with 200,000x magnification. Images were digitized on an ER-50-5megapixel CCD camera. SARS-CoV-2 nanoparticle ferritin cores were measured to have a diameter of about 11-17 nm (Figure 5). [0219] SARS-CoV-2 nanoparticles produced in Expi293 cells were purified as described using AEX and SEC. Distinct immunoreactive fractions eluted during AEX and formulated in 1x PBS were analyzed by DLS to determine the diameter of the particle species. DLS measurements were made at a 173° angle backscatter with the dispersant set as water. The material in the various fractions had a range of diameters (23.7-99.8 nm) (Table 1). On the basis of the various diameters measured, the eluate fractions from SEC were combined into three pools as identified in Table 1. The fractions comprising pool 1 had an average diameter of 30.3 nm; pool 2 fractions had an average diameter of 53.2 nm; and pool 3 had an average diameter of 85.2 nm. Table 1:

[0220] An intact and accessible receptor-binding domain (RBD) on the SARS-CoV-2 spike was confirmed by native Western blot and bio-layer interferometry (BLI) using material produced in Expi293 cells for both methods. It was not known if inactivation of the furin cleavage site would still allow the RBD to remain accessible since furin cleavage in the wild-type spike increases accessibility of the RBD. 3 µg of two different pool 1 and 2 fractions of purified nanoparticles were separated by native PAGE on a 3- 12% precast gel. After electrophoresis, samples were transferred to a PVDF membrane. Membranes were blocked with 3% BSA, probed with the previously mentioned rabbit polyclonal anti-ferritin antiserum, and detected with an anti-rabbit secondary conjugated to alkaline phosphatase. Blots were developed with an BCIP/NBT substrate. Alternatively, membranes were probed with recombinant human ACE2 bearing an in vitro BirA-biotinylated Avitag, detected with a streptavidin-alkaline phosphatase reagent, and developed with BCIP/NBT. Blots probed with the anti-ferritin antiserum showed reactivity to a protein species of high molecular weight. An H. pylori ferritin nanoparticle without a fusion protein was used as a reference marker; this particle has a molecular weight of 456 kDa, and the SARS-CoV-2 nanoparticle migrates behind this reference point in the gel (Figure 6). Similarly, the blots probed with rACE2 demonstrated a high MW protein species, confirming that the particles bear an intact and accessible RBD. [0221] Additional confirmation of an intact and accessible RBD was attained by BLI. C- terminal His-tagged ACE2 at 8 µg/mL was immobilized on HIS1K biosensors for 180 seconds followed by a 120 s baseline. Three pools of SARS-CoV-2 nanoparticles were assayed for ACE2 binding for 200 s. Each pool, regardless of size identified by DLS (Table 1), was able to associate with immobilized ACE2 (Figure 7). Collectively, the native Western blot, TEM, and BLI data confirm that the SARS-CoV-2 – ferritin fusion protein spontaneously assembles into a nanoparticle and contains an RBD that is accessible. Example 3: Immunogenicity of SARS-CoV-2 nanoparticles [0222] The SARS-CoV-2 nanoparticle was tested for its immunogenicity in Equus ferus caballus, the domesticated horse. 0.5 mg of the formulated SARS-CoV-2 nanoparticle (in 1x PBS with 80 mg/mL sucrose) produced in Expi293 cells was mixed 1:1 with Sigma Adjuvant System® oil and administered in a 1 mL volume via the intradermal route. Horses were boosted every 21 days with the same dose and adjuvant. Blood was drawn every seven days and seroconversion was measured by a Luminex®-based assay against the SARS-CoV-2 spike trimer (QHD43416.1, amino acids 16-1213; R683A, R685A), the SARS-CoV-2 S1 subunit (YP _009724390.1, amino acids 16-685), and the SARS-CoV-2 RBD (QHD43416.1, amino acids 319-541; N354D, D364Y). SARS-CoV-2 antigens were coupled to magnetic beads by amine-reactive chemistry and used together in a multiplex assay. Serum was assayed at 1/400 and 1/800 dilutions. Serum equine IgG reactive to the previously mentioned SARS-CoV-2 spike antigens bound the SARS-CoV- 2 antigen on the magnetic beads. Reactive equine IgG was detected using a combination of anti-equine IgG F(ab’)2-biotin and streptavidin-PE reagents. Median fluorescent intensity values were measured to determine seropositivity against the aforementioned antigens. All three of the vaccinated horses (COVI906, COVI907, and COVI908) demonstrated seroconversion against each of the three antigens (Table 2 and Figure 8). Reactivity was highest in magnitude against the SARS-CoV-2 trimer and RBD antigens as determined by MFI. Table 2:

Example 4: Neutralization of SARS-CoV-2 Pseudovirus [0223] Serum drawn on day 28 post-vaccination from a vaccinated horse, COVI908, was assayed for its ability to neutralize a pseudovirus bearing the SARS-CoV-2 spike as well as expressing a luciferase reporter gene. The pseudovirus was assembled by co- transfection of Tat, Gag, Pol, Rev, and TMPRSS2 genes, along with a lentivirus backbone that carried the luciferase gene and a plasmid encoding for the SARS-CoV-2 spike (accession ID YP_009724390). To determine a neutralization titer, the following “PsVN” assay was performed: serial 1:2 dilutions of COVI908 serum were prepared and pre-incubated with a concentration of pseudovirus that produces a suitable infectious titer in each assay well (100TCID50). The sample and virus mixture were combined with cells expressing the ACE-2 receptor. The SARS-CoV-2 spike binds to the ACE-2 receptor, allowing for the entry of the pseudovirus into the host cell. The inoculum was incubated on ACE-2-expressing cells for 65 hours. The number of virus-infected cells was correlated to the luciferase gene expression measured by luminescence intensity (relative luminescence units, RLU). Luciferase activity was measured by the Bright-Glo™ luciferase assay system (Promega). Neutralization was measured by the reduction in luminescence signal. Neutralization was calculated by fitting the luciferase signal to a non-linear curve to determine the 50% neutralizing (EC₅₀) titer. Relative potency was determined by a constrained curve fit of the sample and standard with potency calculated by dividing the EC₅₀ of the sample with the EC₅₀ of the standard. The standard for this assay was an immunoglobulin product manufactured from plasma of convalescent SARS- CoV-2 patients. [0224] Serum from horse COVI908 was calculated to have an EC50 of 521 (reciprocal of serum dilution) based on a 4 parameter logistic fit of the reduction in RLU as a function of serum dilution (Figure 9, open squares). When compared to a human SARS-CoV-2 convalescent plasma product with an EC50 of 515 (Figure 9, open circles), serum from horse COVI908 had a relative potency of 1.20. Sequences SEQ ID NO:1 – expression plasmid GACGGATCGGGAGATCTCCCGATCCCCTATGGTGCACTCTCAGTACAATCTGC TCTGATGCCGCATAGTTAAGCCAGTATCTGCTCCCTGCTTGTGTGTTGGAGGT CGCTGAGTAGTGCGCGAGCAAAATTTAAGCTACAACAAGGCAAGGCTTGACC GACAATTGCATGAAGAATCTGCTTAGGGTTAGGCGTTTTGCGCTGCTTCGCGA TGTACGGGCCAGATATACGCGTTGACATTGATTATTGACTAGTTATTAATAGT AATCAATTACGGGGTCATTAGTTCATAGCCCATATATGGAGTTCCGCGTTACA TAACTTACGGTAAATGGCCCGCCTGGCTGACCGCCCAACGACCCCCGCCCATT GACGTCAATAATGACGTATGTTCCCATAGTAACGCCAATAGGGACTTTCCATT GACGTCAATGGGTGGAGTATTTACGGTAAACTGCCCACTTGGCAGTACATCA AGTGTATCATATGCCAAGTACGCCCCCTATTGACGTCAATGACGGTAAATGG CCCGCCTGGCATTATGCCCAGTACATGACCTTATGGGACTTTCCTACTTGGCA GTACATCTACGTATTAGTCATCGCTATTACCATGGTGATGCGGTTTTGGCAGT ACATCAATGGGCGTGGATAGCGGTTTGACTCACGGGGATTTCCAAGTCTCCA CCCCATTGACGTCAATGGGAGTTTGTTTTGGCACCAAAATCAACGGGACTTTC CAAAATGTCGTAACAACTCCGCCCCATTGACGCAAATGGGCGGTAGGCGTGT ACGGTGGGAGGTCTATATAAGCAGAGCTCTCTGGCTAACTAGAGAACCCACT GCTTACTGGCTTATCGAAATTAATACGACTCACTATAGGGAGACCCAAGCTG GCTAGCCACCATGTTCGTGTTTCTGGTGCTGCTGCCTCTGGTGAGCTCCCAGT GCGTGAACCTGACCACAAGGACCCAGCTGCCACCTGCCTATACCAATTCCTTC ACACGGGGCGTGTACTATCCTGACAAGGTGTTTAGATCTAGCGTGCTGCACA GCACACAGGATCTGTTTCTGCCATTCTTTTCCAACGTGACCTGGTTCCACGCC ATCCACGTGAGCGGCACCAATGGCACAAAGCGGTTCGACAATCCTGTGCTGC CCTTCAACGATGGCGTGTACTTCGCCTCCACCGAGAAGTCTAACATCATCAGA GGCTGGATCTTTGGCACCACACTGGACAGCAAGACACAGTCCCTGCTGATCG TGAACAATGCCACCAACGTGGTCATCAAGGTGTGCGAGTTCCAGTTTTGTAAT GATCCCTTCCTGGGCGTGTACTATCACAAGAACAATAAGTCTTGGATGGAGA GCGAGTTTAGAGTGTATTCCTCTGCCAACAATTGTACATTTGAGTACGTGAGC CAGCCTTTCCTGATGGACCTGGAGGGCAAGCAGGGCAATTTCAAGAACCTGA GGGAGTTCGTGTTTAAGAATATCGATGGCTACTTCAAGATCTACTCTAAGCAC ACCCCTATCAACCTGGTGCGCGACCTGCCACAGGGCTTCAGCGCCCTGGAGC CTCTGGTGGATCTGCCAATCGGCATCAACATCACCCGGTTTCAGACACTGCTG GCCCTGCACAGAAGCTACCTGACACCCGGCGACAGCTCCTCTGGATGGACCG CAGGAGCAGCAGCCTACTATGTGGGCTATCTGCAGCCTAGGACCTTCCTGCTG AAGTACAACGAGAATGGCACCATCACAGACGCCGTGGATTGCGCCCTGGATC CTCTGTCTGAGACAAAGTGTACACTGAAGAGCTTTACCGTGGAGAAGGGCAT CTATCAGACAAGCAATTTCAGGGTGCAGCCAACCGAGTCCATCGTGCGCTTTC CAAATATCACAAACCTGTGCCCCTTTGGCGAGGTGTTCAACGCAACCAGGTTC GCCAGCGTGTACGCATGGAATAGGAAGCGCATCTCCAACTGCGTGGCCGACT ATTCTGTGCTGTACAACTCCGCCTCTTTCAGCACCTTTAAGTGCTATGGCGTGT CCCCCACAAAGCTGAATGACCTGTGCTTTACCAACGTGTACGCCGATTCTTTC GTGATCAGGGGCGACGAGGTGCGCCAGATCGCACCTGGACAGACAGGCAAG ATCGCCGACTACAATTATAAGCTGCCAGACGATTTCACCGGCTGCGTGATCGC CTGGAACTCTAACAATCTGGATAGCAAAGTGGGCGGCAACTACAATTATCTG TACCGGCTGTTTAGAAAGTCCAATCTGAAGCCCTTCGAGAGGGACATCTCCA CAGAGATCTACCAGGCCGGCTCTACCCCTTGCAATGGCGTGGAGGGCTTTAA CTGTTATTTCCCCCTGCAGAGCTACGGCTTCCAGCCTACAAACGGCGTGGGCT ATCAGCCATACCGCGTGGTGGTGCTGAGCTTTGAGCTGCTGCACGCACCAGC AACAGTGTGCGGACCTAAGAAGTCCACCAATCTGGTGAAGAACAAGTGCGTG AACTTCAACTTCAACGGCCTGACCGGAACAGGCGTGCTGACCGAGTCCAACA AGAAGTTCCTGCCATTTCAGCAGTTCGGCAGGGACATCGCAGATACCACAGA CGCCGTGCGCGACCCACAGACCCTGGAGATCCTGGATATCACACCCTGCTCCT TCGGCGGCGTGTCTGTGATCACACCCGGCACCAATACAAGCAACCAGGTGGC CGTGCTGTATCAGGACGTGAATTGTACCGAGGTGCCTGTGGCCATCCACGCC GATCAGCTGACCCCAACATGGCGGGTGTACAGCACCGGCTCCAACGTGTTCC AGACAAGAGCAGGATGCCTGATCGGAGCAGAGCACGTGAACAATTCTTATGA GTGCGACATCCCAATCGGCGCCGGCATCTGTGCCAGCTACCAGACCCAGACA AACTCCCCAAGGAGAGCAGCCTCTGTGGCCTCCCAGTCTATCATCGCCTATAC CATGAGCCTGGGCGCCGAGAATTCCGTGGCCTACTCTAACAATAGCATCGCC ATCCCAACCAACTTCACAATCTCCGTGACCACAGAGATCCTGCCCGTGAGCAT GACCAAGACATCCGTGGACTGCACAATGTATATCTGTGGCGATTCCACCGAG TGCTCTAACCTGCTGCTGCAGTACGGCAGCTTTTGTACCCAGCTGAATAGGGC CCTGACAGGAATCGCAGTGGAGCAGGACAAGAACACACAGGAGGTGTTCGC CCAGGTGAAGCAGATCTACAAGACCCCACCCATCAAGGACTTTGGCGGCTTC AACTTCAGCCAGATCCTGCCAGATCCCTCCAAGCCTTCTAAGCGGAGCTTTAT CGAGGACCTGCTGTTCAACAAGGTGACCCTGGCCGATGCCGGCTTCATCAAG CAGTATGGCGATTGCCTGGGCGACATCGCAGCACGGGACCTGATCTGTGCCC AGAAGTTTAATGGCCTGACCGTGCTGCCTCCACTGCTGACAGATGAGATGAT CGCCCAGTACACATCTGCCCTGCTGGCCGGAACCATCACAAGCGGATGGACC TTCGGCGCAGGAGCCGCCCTGCAGATCCCATTTGCCATGCAGATGGCCTATCG CTTCAACGGCATCGGCGTGACCCAGAATGTGCTGTACGAGAACCAGAAGCTG ATCGCCAATCAGTTTAACTCCGCCATCGGCAAGATCCAGGACTCTCTGAGCTC CACAGCCAGCGCCCTGGGCAAGCTGCAGGATGTGGTGAATCAGAACGCCCAG GCCCTGAATACCCTGGTGAAGCAGCTGTCTAGCAACTTCGGCGCCATCTCCTC TGTGCTGAATGATATCCTGAGCAGGCTGGACCCACCTGAGGCAGAGGTGCAG ATCGACCGGCTGATCACAGGCAGACTGCAGTCTCTGCAGACCTACGTGACAC AGCAGCTGATCAGGGCAGCAGAGATCAGGGCCAGCGCCAATCTGGCAGCAA CCAAGATGAGCGAGTGCGTGCTGGGCCAGTCCAAGAGAGTGGACTTTTGTGG CAAGGGCTATCACCTGATGAGCTTCCCACAGTCCGCCCCACACGGAGTGGTG TTTCTGCACGTGACCTACGTGCCCGCCCAGGAGAAGAACTTCACCACAGCCC CTGCCATCTGCCACGATGGCAAGGCCCACTTTCCAAGGGAGGGCGTGTTCGT GTCCAACGGCACCCACTGGTTTGTGACACAGCGCAATTTCTACGAGCCCCAG ATCATCACCACAGACAATACCTTCGTGAGCGGCAACTGTGACGTGGTCATCG GCATCGTGAACAATACCGTGTATGATCCCCTGCAGCCTGAGCTGGACTCCTTT AAGGAGGAGCTGGATAAGTACTTCAAGAATCACACCTCTCCCGACGTGGATC TGGGCGACATCTCTGGCATCAATGCCAGCGTGGTGAACATCCAGAAGGAGAT CGATCGGCTGAACGAGGTGGCCAAGAATCTGAACGAGAGCCTGATCGACCTG CAGGAGCTGGGCAAGTATGAGCAGGGCTCCGGCGATATCATCAAGCTGCTGA ATGAGCAGGTGAACAAGGAGATGCAGAGCTCCAATCTGTATATGTCCATGTC TAGCTGGTGCTACACCCACTCTCTGGACGGAGCAGGCCTGTTCCTGTTTGATC ACGCCGCCGAGGAGTACGAGCACGCCAAGAAGCTGATCATCTTCCTGAACGA GAACAATGTGCCCGTGCAGCTGACAAGCATCTCCGCCCCTGAGCACAAGTTT GAGGGCCTGACCCAGATCTTCCAGAAGGCCTATGAGCACGAGCAGCACATCT CTGAGAGCATCAACAATATCGTGGACCACGCCATCAAGTCCAAGGATCACGC CACCTTCAACTTTCTGCAGTGGTACGTGGCCGAGCAGCACGAGGAGGAGGTG CTGTTCAAGGATATCCTGGACAAGATCGAGCTGATCGGCAATGAGAACCACG GCCTGTATCTGGCCGACCAGTACGTGAAGGGCATCGCCAAGAGCAGGAAGTC CGGCTCTTGATGATAAGCTTAAGTTTAAACCGCTGATCAGCCTCGACTGTGCC TTCTAGTTGCCAGCCATCTGTTGTTTGCCCCTCCCCCGTGCCTTCCTTGACCCT GGAAGGTGCCACTCCCACTGTCCTTTCCTAATAAAATGAGGAAATTGCATCGC ATTGTCTGAGTAGGTGTCATTCTATTCTGGGGGGTGGGGTGGGGCAGGACAG CAAGGGGGAGGATTGGGAAGACAATAGCAGGCATGCTGGGGATGCGGTGGG CTCTATGGCTTCTGAGGCGGAAAGAACCAGCTGGGGCTCTAGGGGGTATCCC CACGCGCCCTGTAGCGGCGCATTAAGCGCGGCGGGTGTGGTGGTTACGCGCA GCGTGACCGCTACACTTGCCAGCGCCCTAGCGCCCGCTCCTTTCGCTTTCTTC CCTTCCTTTCTCGCCACGTTCGCCGGCTTTCCCCGTCAAGCTCTAAATCGGGG GCTCCCTTTAGGGTTCCGATTTAGTGCTTTACGGCACCTCGACCCCAAAAAAC TTGATTAGGGTGATGGTTCACGTAGTGGGCCATCGCCCTGATAGACGGTTTTT CGCCCTTTGACGTTGGAGTCCACGTTCTTTAATAGTGGACTCTTGTTCCAAAC TGGAACAACACTCAACCCTATCTCGGTCTATTCTTTTGATTTATAAGGGATTTT GCCGATTTCGGCCTATTGGTTAAAAAATGAGCTGATTTAACAAAAATTTAACG CGAATTAATTCTGTGGAATGTGTGTCAGTTAGGGTGTGGAAAGTCCCCAGGCT CCCCAGCAGGCAGAAGTATGCAAAGCATGCATCTCAATTAGTCAGCAACCAG GTGTGGAAAGTCCCCAGGCTCCCCAGCAGGCAGAAGTATGCAAAGCATGCAT CTCAATTAGTCAGCAACCATAGTCCCGCCCCTAACTCCGCCCATCCCGCCCCT AACTCCGCCCAGTTCCGCCCATTCTCCGCCCCATGGCTGACTAATTTTTTTTAT TTATGCAGAGGCCGAGGCCGCCTCTGCCTCTGAGCTATTCCAGAAGTAGTGA GGAGGCTTTTTTGGAGGCCTAGGCTTTTGCAAAAAGCTCCCGGGAGCTTGTAT ATCCATTTTCGGATCTGATCAAGAGACAGGATGAGGATCGTTTCGCATGATTG AACAAGATGGATTGCACGCAGGTTCTCCGGCCGCTTGGGTGGAGAGGCTATT CGGCTATGACTGGGCACAACAGACAATCGGCTGCTCTGATGCCGCCGTGTTC CGGCTGTCAGCGCAGGGGCGCCCGGTTCTTTTTGTCAAGACCGACCTGTCCGG TGCCCTGAATGAACTGCAGGACGAGGCAGCGCGGCTATCGTGGCTGGCCACG ACGGGCGTTCCTTGCGCAGCTGTGCTCGACGTTGTCACTGAAGCGGGAAGGG ACTGGCTGCTATTGGGCGAAGTGCCGGGGCAGGATCTCCTGTCATCTCACCTT GCTCCTGCCGAGAAAGTATCCATCATGGCTGATGCAATGCGGCGGCTGCATA CGCTTGATCCGGCTACCTGCCCATTCGACCACCAAGCGAAACATCGCATCGA GCGAGCACGTACTCGGATGGAAGCCGGTCTTGTCGATCAGGATGATCTGGAC GAAGAGCATCAGGGGCTCGCGCCAGCCGAACTGTTCGCCAGGCTCAAGGCGC GCATGCCCGACGGCGAGGATCTCGTCGTGACCCATGGCGATGCCTGCTTGCC GAATATCATGGTGGAAAATGGCCGCTTTTCTGGATTCATCGACTGTGGCCGGC TGGGTGTGGCGGACCGCTATCAGGACATAGCGTTGGCTACCCGTGATATTGCT GAAGAGCTTGGCGGCGAATGGGCTGACCGCTTCCTCGTGCTTTACGGTATCGC CGCTCCCGATTCGCAGCGCATCGCCTTCTATCGCCTTCTTGACGAGTTCTTCTG AGCGGGACTCTGGGGTTCGAAATGACCGACCAAGCGACGCCCAACCTGCCAT CACGAGATTTCGATTCCACCGCCGCCTTCTATGAAAGGTTGGGCTTCGGAATC GTTTTCCGGGACGCCGGCTGGATGATCCTCCAGCGCGGGGATCTCATGCTGG AGTTCTTCGCCCACCCCAACTTGTTTATTGCAGCTTATAATGGTTACAAATAA AGCAATAGCATCACAAATTTCACAAATAAAGCATTTTTTTCACTGCATTCTAG TTGTGGTTTGTCCAAACTCATCAATGTATCTTATCATGTCTGTATACCGTCGAC CTCTAGCTAGAGCTTGGCGTAATCATGGTCATAGCTGTTTCCTGTGTGAAATT GTTATCCGCTCACAATTCCACACAACATACGAGCCGGAAGCATAAAGTGTAA AGCCTGGGGTGCCTAATGAGTGAGCTAACTCACATTAATTGCGTTGCGCTCAC TGCCCGCTTTCCAGTCGGGAAACCTGTCGTGCCAGCTGCATTAATGAATCGGC CAACGCGCGGGGAGAGGCGGTTTGCGTATTGGGCGCTCTTCCGCTTCCTCGCT CACTGACTCGCTGCGCTCGGTCGTTCGGCTGCGGCGAGCGGTATCAGCTCACT CAAAGGCGGTAATACGGTTATCCACAGAATCAGGGGATAACGCAGGAAAGA ACATGTGAGCAAAAGGCCAGCAAAAGGCCAGGAACCGTAAAAAGGCCGCGT TGCTGGCGTTTTTCCATAGGCTCCGCCCCCCTGACGAGCATCACAAAAATCGA CGCTCAAGTCAGAGGTGGCGAAACCCGACAGGACTATAAAGATACCAGGCGT TTCCCCCTGGAAGCTCCCTCGTGCGCTCTCCTGTTCCGACCCTGCCGCTTACCG GATACCTGTCCGCCTTTCTCCCTTCGGGAAGCGTGGCGCTTTCTCATAGCTCA CGCTGTAGGTATCTCAGTTCGGTGTAGGTCGTTCGCTCCAAGCTGGGCTGTGT GCACGAACCCCCCGTTCAGCCCGACCGCTGCGCCTTATCCGGTAACTATCGTC TTGAGTCCAACCCGGTAAGACACGACTTATCGCCACTGGCAGCAGCCACTGG TAACAGGATTAGCAGAGCGAGGTATGTAGGCGGTGCTACAGAGTTCTTGAAG TGGTGGCCTAACTACGGCTACACTAGAAGAACAGTATTTGGTATCTGCGCTCT GCTGAAGCCAGTTACCTTCGGAAAAAGAGTTGGTAGCTCTTGATCCGGCAAA CAAACCACCGCTGGTAGCGGTGTTTTTTTTGTTTGCAAGCAGCAGATTACGCG CAGAAAAAAAGGATCTCAAGAAGATCCTTTGATCTTTTCTACGGGGTCTGAC GCTCAGTGGAACGAAAACTCACGTTAAGGGATTTTGGTCATGAGATTATCAA AAAGGATCTTCACCTAGATCCTTTTAAATTAAAAATGAAGTTTTAAATCAATC TAAAGTATATATGAGTAAACTTGGTCTGACAGTTACCAATGCTTAATCAGTGA GGCACCTATCTCAGCGATCTGTCTATTTCGTTCATCCATAGTTGCCTGACTCCC CGTCGTGTAGATAACTACGATACGGGAGGGCTTACCATCTGGCCCCAGTGCT GCAATGATACCGCGAGACCCACGCTCACCGGCTCCAGATTTATCAGCAATAA ACCAGCCAGCCGGAAGGGCCGAGCGCAGAAGTGGTCCTGCAACTTTATCCGC CTCCATCCAGTCTATTAATTGTTGCCGGGAAGCTAGAGTAAGTAGTTCGCCAG TTAATAGTTTGCGCAACGTTGTTGCCATTGCTACAGGCATCGTGGTGTCACGC TCGTCGTTTGGTATGGCTTCATTCAGCTCCGGTTCCCAACGATCAAGGCGAGT TACATGATCCCCCATGTTGTGCAAAAAAGCGGTTAGCTCCTTCGGTCCTCCGA TCGTTGTCAGAAGTAAGTTGGCCGCAGTGTTATCACTCATGGTTATGGCAGCA CTGCATAATTCTCTTACTGTCATGCCATCCGTAAGATGCTTTTCTGTGACTGGT GAGTACTCAACCAAGTCATTCTGAGAATAGTGTATGCGGCGACCGAGTTGCT CTTGCCCGGCGTCAATACGGGATAATACCGCGCCACATAGCAGAACTTTAAA AGTGCTCATCATTGGAAAACGTTCTTCGGGGCGAAAACTCTCAAGGATCTTAC CGCTGTTGAGATCCAGTTCGATGTAACCCACTCGTGCACCCAACTGATCTTCA GCATCTTTTACTTTCACCAGCGTTTCTGGGTGAGCAAAAACAGGAAGGCAAA ATGCCGCAAAAAAGGGAATAAGGGCGACACGGAAATGTTGAATACTCATACT CTTCCTTTTTCAATATTATTGAAGCATTTATCAGGGTTATTGTCTCATGAGCGG ATACATATTTGAATGTATTTAGAAAAATAAACAAATAGGGGTTCCGCGCACA TTTCCCCGAAAAGTGCCACCTGACGTC SEQ ID NO:2 – modified spike sequence (leader sequence (amino acids 1-15) underlined) MFVFLVLLPLVSSQCVNLTTRTQLPPAYTNSFTRGVYYPDKVFRSSVLHSTQDLF LPFFSNVTWFHAIHVSGTNGTKRFDNPVLPFNDGVYFASTEKSNIIRGWIFGTTLD SKTQSLLIVNNATNVVIKVCEFQFCNDPFLGVYYHKNNKSWMESEFRVYSSANN CTFEYVSQPFLMDLEGKQGNFKNLREFVFKNIDGYFKIYSKHTPINLVRDLPQGFS ALEPLVDLPIGINITRFQTLLALHRSYLTPGDSSSGWTAGAAAYYVGYLQPRTFLL KYNENGTITDAVDCALDPLSETKCTLKSFTVEKGIYQTSNFRVQPTESIVRFPNITN LCPFGEVFNATRFASVYAWNRKRISNCVADYSVLYNSASFSTFKCYGVSPTKLN DLCFTNVYADSFVIRGDEVRQIAPGQTGKIADYNYKLPDDFTGCVIAWNSNNLDS KVGGNYNYLYRLFRKSNLKPFERDISTEIYQAGSTPCNGVEGFNCYFPLQSYGFQ PTNGVGYQPYRVVVLSFELLHAPATVCGPKKSTNLVKNKCVNFNFNGLTGTGVL TESNKKFLPFQQFGRDIADTTDAVRDPQTLEILDITPCSFGGVSVITPGTNTSNQVA VLYQDVNCTEVPVAIHADQLTPTWRVYSTGSNVFQTRAGCLIGAEHVNNSYECD IPIGAGICASYQTQTNSPRRAASVASQSIIAYTMSLGAENSVAYSNNSIAIPTNFTIS VTTEILPVSMTKTSVDCTMYICGDSTECSNLLLQYGSFCTQLNRALTGIAVEQDK NTQEVFAQVKQIYKTPPIKDFGGFNFSQILPDPSKPSKRSFIEDLLFNKVTLADAGF IKQYGDCLGDIAARDLICAQKFNGLTVLPPLLTDEMIAQYTSALLAGTITSGWTFG AGAALQIPFAMQMAYRFNGIGVTQNVLYENQKLIANQFNSAIGKIQDSLSSTASA LGKLQDVVNQNAQALNTLVKQLSSNFGAISSVLNDILSRLDPPEAEVQIDRLITGR LQSLQTYVTQQLIRAAEIRASANLAATKMSECVLGQSKRVDFCGKGYHLMSFPQ SAPHGVVFLHVTYVPAQEKNFTTAPAICHDGKAHFPREGVFVSNGTHWFVTQRN FYEPQIITTDNTFVSGNCDVVIGIVNNTVYDPLQPELDSFKEELDKYFKNHTSPDV DLGDISGINASVVNIQKEIDRLNEVAKNLNESLIDLQELGKYEQ SEQ ID NO:3 – modified ferritin DIIKLLNEQVNKEMQSSNLYMSMSSWCYTHSLDGAGLFLFDHAAEEYEHAKKLII FLNENNVPVQLTSISAPEHKFEGLTQIFQKAYEHEQHISESINNIVDHAIKSKDHAT FNFLQWYVAEQHEEEVLFKDILDKIELIGNENHGLYLADQYVKGIAKSRKSGS SEQ ID NO:4 – linker GSG SEQ ID NO:5 – SARS-CoV-2 spike protein sequence (GenBank: QHD43416.1) (leader sequence (amino acids 1-15) underlined) MFVFLVLLPLVSSQCVNLTTRTQLPPAYTNSFTRGVYYPDKVFRSSVLHSTQDLF LPFFSNVTWFHAIHVSGTNGTKRFDNPVLPFNDGVYFASTEKSNIIRGWIFGTTLD SKTQSLLIVNNATNVVIKVCEFQFCNDPFLGVYYHKNNKSWMESEFRVYSSANN CTFEYVSQPFLMDLEGKQGNFKNLREFVFKNIDGYFKIYSKHTPINLVRDLPQGFS ALEPLVDLPIGINITRFQTLLALHRSYLTPGDSSSGWTAGAAAYYVGYLQPRTFLL KYNENGTITDAVDCALDPLSETKCTLKSFTVEKGIYQTSNFRVQPTESIVRFPNITN LCPFGEVFNATRFASVYAWNRKRISNCVADYSVLYNSASFSTFKCYGVSPTKLN DLCFTNVYADSFVIRGDEVRQIAPGQTGKIADYNYKLPDDFTGCVIAWNSNNLDS KVGGNYNYLYRLFRKSNLKPFERDISTEIYQAGSTPCNGVEGFNCYFPLQSYGFQ PTNGVGYQPYRVVVLSFELLHAPATVCGPKKSTNLVKNKCVNFNFNGLTGTGVL TESNKKFLPFQQFGRDIADTTDAVRDPQTLEILDITPCSFGGVSVITPGTNTSNQVA VLYQDVNCTEVPVAIHADQLTPTWRVYSTGSNVFQTRAGCLIGAEHVNNSYECD IPIGAGICASYQTQTNSPRRARSVASQSIIAYTMSLGAENSVAYSNNSIAIPTNFTIS VTTEILPVSMTKTSVDCTMYICGDSTECSNLLLQYGSFCTQLNRALTGIAVEQDK NTQEVFAQVKQIYKTPPIKDFGGFNFSQILPDPSKPSKRSFIEDLLFNKVTLADAGF IKQYGDCLGDIAARDLICAQKFNGLTVLPPLLTDEMIAQYTSALLAGTITSGWTFG AGAALQIPFAMQMAYRFNGIGVTQNVLYENQKLIANQFNSAIGKIQDSLSSTASA LGKLQDVVNQNAQALNTLVKQLSSNFGAISSVLNDILSRLDKVEAEVQIDRLITG RLQSLQTYVTQQLIRAAEIRASANLAATKMSECVLGQSKRVDFCGKGYHLMSFP QSAPHGVVFLHVTYVPAQEKNFTTAPAICHDGKAHFPREGVFVSNGTHWFVTQR NFYEPQIITTDNTFVSGNCDVVIGIVNNTVYDPLQPELDSFKEELDKYFKNHTSPD VDLGDISGINASVVNIQKEIDRLNEVAKNLNESLIDLQELGKYEQYIKWPWYIWL GFIAGLIAIVMVTIMLCCMTSCCSCLKGCCSCGSCCKFDEDDSEPVLKGVKLHYT SEQ ID NO:6 – modified spike:linker:ferritin (leader sequence (amino acids 1-15) underlined) MFVFLVLLPLVSSQCVNLTTRTQLPPAYTNSFTRGVYYPDKVFRSSVLHSTQDLF LPFFSNVTWFHAIHVSGTNGTKRFDNPVLPFNDGVYFASTEKSNIIRGWIFGTTLD SKTQSLLIVNNATNVVIKVCEFQFCNDPFLGVYYHKNNKSWMESEFRVYSSANN CTFEYVSQPFLMDLEGKQGNFKNLREFVFKNIDGYFKIYSKHTPINLVRDLPQGFS ALEPLVDLPIGINITRFQTLLALHRSYLTPGDSSSGWTAGAAAYYVGYLQPRTFLL KYNENGTITDAVDCALDPLSETKCTLKSFTVEKGIYQTSNFRVQPTESIVRFPNITN LCPFGEVFNATRFASVYAWNRKRISNCVADYSVLYNSASFSTFKCYGVSPTKLN DLCFTNVYADSFVIRGDEVRQIAPGQTGKIADYNYKLPDDFTGCVIAWNSNNLDS KVGGNYNYLYRLFRKSNLKPFERDISTEIYQAGSTPCNGVEGFNCYFPLQSYGFQ PTNGVGYQPYRVVVLSFELLHAPATVCGPKKSTNLVKNKCVNFNFNGLTGTGVL TESNKKFLPFQQFGRDIADTTDAVRDPQTLEILDITPCSFGGVSVITPGTNTSNQVA VLYQDVNCTEVPVAIHADQLTPTWRVYSTGSNVFQTRAGCLIGAEHVNNSYECD IPIGAGICASYQTQTNSPRRAASVASQSIIAYTMSLGAENSVAYSNNSIAIPTNFTIS VTTEILPVSMTKTSVDCTMYICGDSTECSNLLLQYGSFCTQLNRALTGIAVEQDK NTQEVFAQVKQIYKTPPIKDFGGFNFSQILPDPSKPSKRSFIEDLLFNKVTLADAGF IKQYGDCLGDIAARDLICAQKFNGLTVLPPLLTDEMIAQYTSALLAGTITSGWTFG AGAALQIPFAMQMAYRFNGIGVTQNVLYENQKLIANQFNSAIGKIQDSLSSTASA LGKLQDVVNQNAQALNTLVKQLSSNFGAISSVLNDILSRLDPPEAEVQIDRLITGR LQSLQTYVTQQLIRAAEIRASANLAATKMSECVLGQSKRVDFCGKGYHLMSFPQ SAPHGVVFLHVTYVPAQEKNFTTAPAICHDGKAHFPREGVFVSNGTHWFVTQRN FYEPQIITTDNTFVSGNCDVVIGIVNNTVYDPLQPELDSFKEELDKYFKNHTSPDV DLGDISGINASVVNIQKEIDRLNEVAKNLNESLIDLQELGKYEQGSGDIIKLLNEQ VNKEMQSSNLYMSMSSWCYTHSLDGAGLFLFDHAAEEYEHAKKLIIFLNENNVP VQLTSISAPEHKFEGLTQIFQKAYEHEQHISESINNIVDHAIKSKDHATFNFLQWY VAEQHEEEVLFKDILDKIELIGNENHGLYLADQYVKGIAKSRKSGS SEQ ID NO:7 – ferritin protein sequence (WP_000949190.1) MLSKDIIKLLNEQVNKEMNSSNLYMSMSSWCYTHSLDGAGLFLFDHAAEEYEH AKKLIIFLNENNVPVQLTSISAPEHKFEGLTQIFQKAYEHEQHISESINNIVDHAIKS KDHATFNFLQWYVAEQHEEEVLFKDILDKIELIGNENHGLYLADQYVKGIAKSR KS * * * [0225] All references (e.g., publications or patents or patent applications) cited herein are incorporated herein by reference in their entirety and for all purposes to the same extent as if each individual reference (e.g., publication or patent or patent application) was specifically and individually indicated to be incorporated by reference in its entirety for all purposes.

Claims

WHAT IS CLAIMED IS: 1. A protein comprising (i) a coronavirus spike polypeptide or a fragment thereof and (ii) a modified ferritin polypeptide or fragment thereof, wherein the coronavirus spike polypeptide or a fragment thereof and the modified ferritin polypeptide or fragment thereof are fused, and wherein the modified ferritin polypeptide or fragment thereof comprises a mutation that removes an N-linked glycosylation site.

2. The protein of claim 1, wherein the coronavirus spike polypeptide or fragment thereof is a modified coronavirus spike polypeptide or fragment thereof.

3. The protein of claim 2, wherein the modified coronavirus spike polypeptide or fragment thereof is capable of binding to ACE2 and (i) comprises a mutation that reduces or eliminates furin cleavage and/or (ii) comprises a mutation that stabilizes a pre-fusion conformation of the polypeptide or fragment there.

4. The protein of claim 3, wherein the mutation that reduces or eliminates furin cleavage comprises a substitution of the amino acid corresponding to R685 in SEQ ID NO:5

5. The protein of claim 1, wherein the coronavirus spike polypeptide or fragment thereof is a naturally occurring coronavirus spike polypeptide or fragment thereof.

6. A protein comprising a modified coronavirus spike polypeptide or a fragment thereof, wherein the spike polypeptide or fragment thereof (i) is capable of binding to ACE2, (ii) comprises a mutation that reduces or eliminates furin cleavage, wherein the mutation that reduces or eliminates furin cleavage comprises a substitution of the amino acid corresponding to R685 in SEQ ID NO:5, and (iii) comprises a mutation that stabilizes a pre-fusion conformation of the polypeptide or fragment thereof.

7. The protein of claim 6, wherein the protein further comprises a ferritin polypeptide or fragment thereof fused to the modified coronavirus spike polypeptide or fragment thereof.

8. The protein of claim 7, wherein the ferritin polypeptide or fragment thereof is a modified ferritin polypeptide or fragment thereof.

9. The protein of claim 8, wherein the modified ferritin polypeptide or fragment thereof comprises a mutation that removes an N-linked glycosylation site.

10. The protein of claim 7, wherein the ferritin polypeptide or fragment thereof is a naturally occurring ferritin polypeptide or fragment thereof.

11. The protein of any one of claims 1-10, wherein the coronavirus is severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

12. The protein of any one of claims 3, 4, and 6-11, wherein the mutation that reduces or eliminates furin cleavage does not comprise a deletion of any amino acids corresponding to R682 to R685 in SEQ ID NO:5.

13. The protein of any one of claims 3, 4, and 6- 12, wherein the mutation that reduces or eliminates furin cleavage consists of a substitution of the amino acid corresponding to R685 in SEQ ID NO:5.

14. The protein of claim 13, wherein the amino acid corresponding to R685 in SEQ ID NO:5 is substituted with an alanine (A).

15. The protein of any one of claims 3, 4, and 6-14, wherein the mutation that stabilizes a pre- fusion conformation comprises a mutation of the amino acid corresponding to K986 and/or the amino acid corresponding to V987 in SEQ ID NO:5.

16. The protein of claim 15, wherein the mutation that stabilizes a pre-fusion conformation consists of a mutation of the amino acid corresponding to K986 to proline (P) in SEQ ID NO:5 and a mutation of the amino acid corresponding to V987 to proline (P) in SEQ ID NO:5.

17. The protein of any one of claims 2-4 and 6-16, wherein the modified coronavirus spike polypeptide or fragment thereof is at least 90%, 95%, 96%, 97%, 98%, or 99% identical to amino acids 16-1,208 of SEQ ID NO:2.

18. The protein of any one of claims 2-4 and 6-17, wherein the modified coronavirus spike polypeptide or fragment thereof comprises 2-10, 2-8, 2-6, 2-5, 2-4, or 2-3 mutations as compared to amino acids 16-1,208 of SEQ ID NO:2.

19. The protein of claim 18, wherein the 2-10, 2-8, 2-6, 2-5, 2-4, or 2-3 mutations are amino acid substitutions.

20. The protein of any one of claims 2-4 and 6-19, wherein the modified coronavirus spike polypeptide or fragment thereof is at least 1000 amino acids in length, at least 1050 amino acids in length, at least 1100 amino acids in length, at least 1150 amino acids in length, at least 1175 amino acids in length, or at least 1190 amino acids in length.

21. The protein of any one of claims 2-4 and 6-20, wherein the modified coronavirus spike polypeptide or fragment thereof comprises the amino acid sequence of amino acids 16- 1,208 of SEQ ID NO:2.

22. The protein of any one of claims 2-4 and 6-21, wherein the modified coronavirus spike polypeptide or fragment thereof is no more than 1250 amino acids in length, no more than 1225 amino acids in length, or no more than 1210 amino acid in length.

23. The protein of any one of claims 2-4 and 6-22, wherein the modified coronavirus spike polypeptide or fragment thereof is about 1150 to about 1210 amino acids in length.

24. The protein of any one of claims 1-23, wherein the protein does not comprise amino acids 1209-1273 of SEQ ID NO:5.

25. The protein of any one of claims 1-5 and 7-24, wherein the ferritin polypeptide or fragment thereof is a Helicobacter pylori ferritin polypeptide or fragment thereof or wherein the modified ferritin polypeptide or fragment thereof is a modified Helicobacter pylori ferritin polypeptide or fragment thereof.

26. The protein of any one of claims 1-5, 9, and 11-25, wherein the mutation that removes an N-linked glycosylation site comprises a substitution of the amino acid corresponding to N19 in SEQ ID NO:7.

27. The protein of claim 26, wherein the amino acid corresponding to N19 in SEQ ID NO:7 is substituted with an glutamine (Q).

28. The protein of any one of claims 1-5 and 7-27 , wherein the ferritin polypeptide or fragment thereof or the modified ferritin polypeptide or fragment thereof is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of SEQ ID NO:3.

29. The protein of any one of claims 1-5 and 7-28, wherein the ferritin polypeptide or fragment thereof or the modified ferritin polypeptide or fragment thereof comprises the amino acid sequence of SEQ ID NO:3.

30. The protein of any one of claims 1-5 and 7-29, wherein the coronavirus spike polypeptide or fragment thereof or the modified coronavirus spike polypeptide or fragment thereof is C-terminal to the ferritin polypeptide or fragment thereof or the modified ferritin polypeptide or fragment thereof.

31. The protein of any one of claims 1-5 and 7-30, wherein the coronavirus spike polypeptide or fragment thereof or the modified coronavirus spike polypeptide or fragment protein and the ferritin polypeptide or fragment thereof or the modified ferritin polypeptide or fragment thereof are fused via a linker.

32. The protein of claim 31, wherein the linker is a polypeptide.

33. The protein of claim 32, wherein the linker polypeptide is a glycine-serine polypeptide.

34. The protein of claim 32 or 33, wherein the linker polypeptide is about 2 to about 5 or about 2 to about 3 amino acids in length.

35. The protein of any one of claims 31-34, wherein the linker comprises the amino acid sequence of SEQ ID NO:4.

36. The protein of any one of claims 1-5 and 7-35, wherein the coronavirus spike polypeptide or fragment thereof or the modified coronavirus spike polypeptide or fragment protein is fused directly to the ferritin polypeptide or fragment thereof or the modified ferritin polypeptide or fragment thereof.

37. A protein comprising amino acids 16-1,376 of SEQ ID NO:6.

38. The protein of any one of claims 1-5 and 7-37, wherein the protein is capable of self- assembling into a nanoparticle comprising a core and an outer portion, wherein the ferritin polypeptide or fragment thereof or the modified ferritin polypeptide or fragment thereof forms the core and the coronavirus spike polypeptide or fragment thereof or the modified coronavirus spike polypeptide or fragment protein forms the outer portion.

39. A trimer comprising the protein of any one of claims 1-38.

40. A trimer comprising three monomers, wherein each of the three monomers comprises the protein of any one of claims 1-38.

41. A nanoparticle comprising the protein of any one of claims 1-38 or the trimer of claim 39 or 40.

42. A nanoparticle comprising trimers, wherein each trimer is the trimer of claim 39 or 40.

43. The nanoparticle of claim 41 or 42, wherein the nanoparticle displays trimers on its surface.

44. The nanoparticle of any one of claims 41-43, wherein the nanoparticle comprises 8 trimers.

45. The nanoparticle of any one of claims 41-44, wherein the nanoparticle has octahedral symmetry.

46. The nanoparticle of any one of claims 41-45, wherein the nanoparticle has a hydrodynamic radius of about 20 to about 60 or about 35 to about 50 nanometers as measured by dynamic light scattering.

47. The nanoparticle of any one of claims 41-46, wherein the nanoparticle comprises a ferritin core that has a radius of about 12 nanometers as measured by transmission electron microscopy.

48. The nanoparticle of any one of claims 41-47, wherein the nanoparticle comprises a core and an outer portion, wherein the ferritin polypeptide or fragment thereof or the modified ferritin polypeptide or fragment thereof forms the core and the coronavirus spike polypeptide or fragment thereof or the modified coronavirus spike polypeptide or fragment protein forms the outer portion

49. The protein, trimer, or nanoparticle of any one of claims 1-48, which is capable of binding to ACE2.

50. The protein, trimer, or nanoparticle of any one of claims 1-49, which is isolated.

51. The protein, trimer, or nanoparticle, of any one of claims 1-50, which is capable of eliciting an immune response to the modified coronavirus spike polypeptide or a fragment thereof in a mammal, optionally wherein the mammal is a horse.

52. The protein, trimer, or nanoparticle of claim 51, wherein the immune response is capable of neutralizing a wild-type coronavirus in an in vitro infection assay, optionally wherein the wild-type coronavirus is wild-type SARS-CoV-2.

53. A nucleic acid comprising a polynucleotide sequence encoding the protein of any one of claims 1-38.

54. A nucleic acid comprising a polynucleotide comprising nucleotides 905-5032 of SEQ ID NO:1.

55. A vector comprising the nucleic acid of claim 53 or 54.

56. The vector of claim 55, wherein the vector further comprises a promoter, optionally wherein the promoter is a CMV promoter.

57. A nucleic acid comprising a polynucleotide comprising the nucleic acid sequence of SEQ ID NO:1.

58. A vector comprising the nucleic acid of claim 56.

59. A host cell comprising the nucleic acid of claim 53, 54, or 57 or the vector of claim 55, 56, or 58, optionally wherein the host cell is a 293 cell or a 293F cell.

60. A method of producing a trimer or a nanoparticle comprising culturing the host cell of claim 59 under conditions suitable for the assembly of a trimer or nanoparticle.

61. The method of claim 60, wherein the method further comprises isolating the trimer or the nanoparticle from the cell culture, optionally wherein the isolating comprises anion exchange chromatography and/or size exclusion chromatography.

62. A trimer or nanoparticle produced by the method of claim 60 or 61.

63. An immunogenic composition comprising the protein, trimer, or nanoparticle of any one of claims 1-52 and 62.

64. A pharmaceutical composition comprising the protein, trimer, or nanoparticle of any one of claims 1-52 and 62 and a pharmaceutically acceptable excipient.

65. A vaccine composition comprising the protein, trimer, or nanoparticle of any one of claims 1-52 and 62.

66. The composition of any one of claims 63-65, wherein at least 95% of trimers in the composition are in pre-fusion conformation.

67. The composition of any one of claims 63-65, wherein the composition further comprises an adjuvant.

68. A method of vaccinating an animal, the method comprising administering the protein, trimer, nanoparticle, or composition of any one of claims 1-52 and 62-67, such that the animal produces an immune response against the protein, trimer, or nanoparticle.

69. The method of claim 68, wherein the immune response is capable of neutralizing wild- type coronavirus in an in vitro infection assay, optionally wherein the wild-type coronavirus is wild-type SARS-CoV-2.

70. The method of claim 68 or 69, wherein the immune response is capable of neutralizing a coronavirus pseudovirus with spike protein in an in vitro infection assay, optionally wherein the coronavirus pseudovirus is a SARS-CoV-2 pseudovirus with a SARS-CoV-2 spike protein.

71. A method of making antibodies or antigen-binding fragments thereof that specifically bind to the spike protein of a coronavirus, comprising administering the protein, trimer, nanoparticle, or composition of any one of claims 1-52 and 62-67 to an animal, such that the animal produces antibodies or antigen-binding fragments thereof that bind to the protein, trimer, or nanoparticle, optionally wherein the coronavirus is SARS-CoV-2.

72. The method of claim 71, wherein the antibodies or antigen-binding fragments thereof are capable of neutralizing wild-type coronavirus in an in vitro infection assay, optionally wherein the coronavirus is SARS-CoV-2.

73. The method of claim 71 or 72, wherein the antibodies or antigen-binding fragments thereof are capable of neutralizing a coronavirus pseudovirus with spike protein in an in vitro infection assay, optionally wherein the coronavirus pseudovirus is a SARS-CoV-2 pseudovirus with a SARS-CoV-2 spike protein

74. The method of any one of claims 68-73, wherein the animal is a horse, a sheep, a goat, a camel, a cow, or a human.

75. The method of claim 74, wherein the animal is a horse.

76. The method of any one of claims 71-75, further comprising isolating the antibodies or antigen-binding fragments thereof from the animal to produce an isolated composition.

77. The method of any one of claims 71-75, further comprising isolating a gamma globulin (IgG) fraction from plasma of the animal to produce an isolated composition.

78. The method of claim 76 or 77, further comprising solvent- and detergent-treating the isolated composition, optionally wherein the solvent and detergent treatment uses tri-n- butyl phosphate and Triton X-100.

79. The method of any one of claims 76-78, further comprising treating the isolated composition to reduce procoagulation activity.

80. The method of any one of claims 76-79, further comprising subjecting the isolated composition to virus filtration.

81. The method of any one of claims 76-80, further comprising subjecting the isolated composition to anion-exchange column chromatography.

82. The method of any one of claims 76-81, further comprising subjecting the isolated composition to cation-exchange chromatography.

83. The method of any one of claims 76-82, further comprising subjecting the isolated composition to pepsin digestion.

84. The method of any one of claims 76-83, further comprising processing the antibodies or antigen-binding fragments thereof to produce a composition comprising Fab, F(ab’)2 and/or F(ab’)2-related fragments.

85. The method of claim 85, wherein the composition comprising Fab, F(ab’)2 and/or F(ab’)2-related fragments comprises no more than 5% intact monomeric IgG antibodies.

86. A composition comprising an antibody or antigen-binding fragment thereof produced by the method of any one of claims 71-85.

87. A pharmaceutical composition comprising an antibody or antigen-binding fragment thereof produced by the method of any one of claims 71-85 and a pharmaceutically acceptable excipient.

88. A composition comprising a mixture of antibodies or antigen-binding fragments thereof produced by the method of any one of claims 71-85.

89. A pharmaceutical composition comprising a mixture of antibodies or antigen-binding fragments thereof produced by the method of any one of claims 71-85 and a pharmaceutically acceptable excipient.

90. The composition of any one of claims 86-89, wherein the antibodies or antigen-binding fragments thereof in the composition comprises an increased percentage of antibodies or antigen-binding fragments that bind to the pre-fusion conformation of a coronavirus spike protein as compared to a mixture of antibodies or antigen-binding fragments produced using a wild-type coronavirus spike protein or fragment thereof.

91. A composition comprising a mixture of antibodies or antigen-binding fragments thereof that bind to the protein, trimer, nanoparticle, or composition of any one of claims 1-52 and 62-67, wherein the composition comprises an increased percentage of antibodies or antigen-binding fragments that bind to the pre-fusion conformation of a coronavirus spike protein as compared to a mixture of antibodies or antigen-binding fragments produced using a wild-type coronavirus spike protein or fragment thereof.

92. A pharmaceutical composition comprising (i) a mixture of antibodies or antigen-binding fragments thereof that bind to the protein, trimer, nanoparticle, or composition of any one of claims 1-52 and 62-67, wherein the composition comprises an increased percentage of antibodies or antigen-binding fragments that bind to the pre-fusion conformation of a coronavirus spike protein as compared to a mixture of antibodies or antigen-binding fragments produced using a wild-type coronavirus spike protein or fragment thereof and (ii) a pharmaceutically acceptable excipient.

93. The composition of any one of claims 88-92, wherein the mixture of antibodies or antigen-binding fragments thereof comprises equine antibodies or antigen-binding fragments thereof.

94. The composition of any one of claims 86-93, wherein the composition comprises Fab, F(ab’)2 and/or F(ab’)2-related fragments.

95. The composition of any one of claims 86-94, wherein the composition comprises a purified gamma globulin (IgG) fraction of equine plasma.

96. The composition of any one of claims 86-95, wherein the composition is a liquid.

97. The composition of any one of claims 86-96, wherein the composition comprises about 100 mg protein /mL or about 50 mg protein /mL.

98. The composition of any one of claims 86-97, wherein the composition comprises about 2 to about 20 % antibodies or antigen-binding fragments thereof by weight.

99. The composition of any one of claims 86-98, further comprising a stabilizing agent.

100. The composition of any one of claims 86-99, wherein composition has a pH of about 4 to about 6, about 5.5 to about 6, or about 5.7.

101. The composition of any one of claims 86-100, wherein the composition is a filtered sterile solution.

102. A method of treating or preventing a coronavirus infection in a subject comprising administering to the subject the composition of any one of claims 86-101, optionally wherein the coronavirus infection is a SARS-CoV-2 infection.

103. The method of claim 102, wherein the composition is administered intravenously.

104. The method of claim 102, wherein the composition is administered intramuscularly.

105. The method of any one of claims 102-104, wherein the composition is only administered once.

106. The method of any one of claims 102-104, wherein the composition is administered at least twice.

107. The method of any one of 102-106, wherein the administration increases the anti- coronavirus antibodies or antigen-binding fragments thereof in the subject by at least 2- fold, by at least 3-fold, by at least 4-fold, or by at least 5-fold.

108. The method of any one of claims 102-107, wherein the administration increases the subject’s immunity to coronavirus.

109. The method of any one of claims 102-108, wherein the administration promotes clearance of coronavirus, optionally wherein the coronavirus is SARS-CoV-2.

110. The method of any one of claims 102-109, wherein the administration decreases the severity of a symptom of coronavirus infection.

111. The method of any one of claims 102-110, wherein the subject is human.

112. The method of any one of claims 102-111, wherein the subject is hospitalized.