Exposure to BA.4/BA.5 Spike glycoprotein drives pan-Omicron neutralization in vaccine-experienced humans and mice

The SARS-CoV-2 Omicron variant and its sublineages show pronounced viral escape from neutralizing antibodies elicited by vaccination or prior SARS-CoV-2 variant infection owing to over 30 amino acid alterations within the spike (S) glycoprotein. We and others have recently reported that breakthrough infection of vaccinated individuals with Omicron sublineages BA.1 and BA.2 are associated with distinct patterns of cross-neutralizing activity against SARS-CoV-2 variants of concern (VOCs). BA.2 breakthrough infection mediated overall stronger cross-neutralization of BA.2 and its descendants (BA.2.12.1, BA.4, and BA.5) compared to BA.1 breakthrough infection. Here we characterized the effect of Omicron BA.4/BA.5 S glycoprotein exposure on the magnitude and breadth of the neutralizing antibody response upon breakthrough infection in vaccinated individuals and in mice upon booster vaccination. We show that immune sera from triple mRNA-vaccinated individuals with subsequent Omicron BA.4/BA.5 breakthrough infection display broad and robust neutralizing activity against Omicron BA.1, BA.2, BA.2.12.1, and BA.4/BA.5. Administration of a prototypic BA.4/BA.5-adapted mRNA booster vaccine to mice following SARS-CoV-2 wild-type strain-based primary immunization is associated with similarly broad neutralizing activity. Immunization of naive mice with a bivalent mRNA vaccine (wild-type + Omicron BA.4/BA.5) induces strong and broad neutralizing activity against Omicron VOCs and previous variants. These findings suggest that when administered as boosters, mono- and bivalent Omicron BA.4/BA.5-adapted vaccines may enhance neutralization breadth, and in a bivalent format may also have the potential to confer protection to individuals with no pre-existing immunity against SARS-CoV-2. ### Competing Interest Statement U.S. and O.T. are management board members and employees at BioNTech SE. A.M., B.G.L., M.B., A.W., A.T., A.G., C.C., V.M., G.J.V., J.M., T.Z., S.F., J.R., F.W., K.S., H.H., K.C.W., J.G., S.S., A.F., K.K., O.O., and A.B.V. are employees at BioNTech SE. K.G., N.K. and S.C. are employees at the University Hospital, Goethe University Frankfurt. Q.Y., H.C., and K.A.S. are employees of Pfizer and may hold stock options. U.S., O.T. A.B.V., A.G., T.Z., J.R., K.C.W. and A.M. are inventors on patents and patent applications related to RNA technology and COVID-19 vaccines. Q.Y, H.C., and K.A.S. are inventors on a patent application related to RNA-based COVID-19 vaccines. U.S., O.T., A.M., B.G.L., K.K., A.W., M.B., A.F., A.T., A.G., V.M., G.J.S., A.B.V. and O.O. have securities from BioNTech SE. S.C. has received an honorarium for serving on a clinical advisory board for BioNTech.