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The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants in the Omicron lineage has resulted in diminished Coronavirus Disease 2019 (COVID-19) vaccine efficacy and persistent transmission. In this study, we evaluated the immunogenicity and protective efficacy of two, recently authorized, bivalent COVID-19 vaccines that contain two mRNAs encoding Wuhan-1 and either BA.1 (mRNA-1273.214) or BA.4/5 (mRNA-1273.222) spike proteins. As a primary two-dose immunization series in mice, both bivalent vaccines induced greater neutralizing antibody responses against Omicron variants than the parental, monovalent mRNA-1273 vaccine. When administered to mice as a booster at 7 months after the primary vaccination series with mRNA-1273, the bivalent vaccines induced broadly neutralizing antibody responses. Whereas most anti-Omicron receptor binding domain antibodies in serum induced by mRNA-1273, mRNA-1273.214 and mRNA-1273.222 boosters cross-reacted with the antecedent Wuhan-1 spike antigen, the mRNA-1273.214 and mRNA-1273.222 bivalent vaccine boosters also induced unique BA.1-specific and BA.4/5-specific responses, respectively. Although boosting with parental or bivalent mRNA vaccines substantially improved protection against BA.5 compared to mice receiving two vaccine doses, the levels of infection, inflammation and pathology in the lung were lowest in animals administered the bivalent mRNA vaccines. Thus, boosting with bivalent Omicron-based mRNA-1273.214 or mRNA-1273.222 vaccines enhances immunogenicity and confers protection in mice against a currently circulating SARS-CoV-2 strain., (© 2022. The Author(s), under exclusive licence to Springer Nature America, Inc.)

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in 2019 has led to the development of a large number of vaccines, several of which are now approved for use in humans. Understanding vaccine-elicited antibody responses against emerging SARS-CoV-2 variants of concern (VOCs) in real time is key to inform public health policies. Serum neutralizing antibody titers are the current best correlate of protection from SARS-CoV-2 challenge in non-human primates and a key metric to understand immune evasion of VOCs. We report that vaccinated BALB/c mice do not recapitulate faithfully the breadth and potency of neutralizing antibody responses elicited by various vaccine platforms against VOCs, compared with non-human primates or humans, suggesting caution should be exercised when interpreting data obtained with this animal model., Competing Interests: Declaration of interests A.C.W., N.P.K., and D.V. are named as inventors on patent applications filed by the University of Washington based on the RBD-NP presented in this paper. N.P.K. is a co-founder, shareholder, paid consultant, and chair of the scientific advisory board of Icosavax, Inc., and the King lab has received an unrelated sponsored research agreement from Pfizer. M.S.D. is a consultant for Inbios, Vir Biotechnology, and Carnival Corporation, and on the Scientific Advisory Boards of Moderna and Immunome. The Diamond laboratory has received unrelated funding support in sponsored research agreements from Vir Biotechnology, Kaleido, and Emergent BioSolutions and past support from Moderna not related to these studies. K.W., A.C., and D.K.E are employees of Moderna and hold stock/stock options in the company. D.H.F. has equity interest in HDT Bio., (Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.)

The large number of spike substitutions in Omicron lineage variants (BA.1, BA.1.1., and BA.2) could jeopardize the efficacy of SARS-CoV-2 vaccines. We evaluated in mice the protective efficacy of the Moderna mRNA-1273 vaccine against BA.1 before or after boosting. Whereas two doses of mRNA-1273 vaccine induced high levels of neutralizing antibodies against historical WA1/2020 strains, lower levels against BA.1 were associated with breakthrough infection and inflammation in the lungs. A primary vaccination series with mRNA-1273.529, an Omicron-matched vaccine, potently neutralized BA.1 but inhibited historical or other SARS-CoV-2 variants less effectively. However, boosting with either mRNA-1273 or mRNA-1273.529 vaccines increased neutralizing titers and protection against BA.1 and BA.2 infection. Nonetheless, the neutralizing antibody titers were higher, and lung viral burden and cytokines were slightly lower in mice boosted with mRNA-1273.529 and challenged with BA.1. Thus, boosting with mRNA-1273 or mRNA-1273.529 enhances protection against Omicron infection with limited differences in efficacy measured., Competing Interests: Declaration of interests M.S.D. is a consultant for Inbios, Vir Biotechnology, Senda Biosciences, and Carnival Corporation, and on the scientific advisory boards of Moderna and Immunome. The Diamond laboratory has received unrelated funding support in sponsored research agreements from J. Virol. Biotechnol., Kaleido, and Emergent BioSolutions and past support from Moderna not related to these studies. K.W., D.L., L.E.A., L.M., T.K., C.S., A.W., A.C., S.M.E., G.-Y.C., G.S.-J., I.R., A.M., Y.-T.L., and D.K.E. are employees of and shareholders in Moderna., (Copyright © 2022 Elsevier Inc. All rights reserved.)