Mellis, I. A.; Wu, M.; Wang, Q.; Bowen, A.; Gherasim, C.; Pierce, V. M.; Shah, J. G.; Purpura, L. J.; Yin, M. T.; Gordon, A.; Guo, Y.; Ho, D. D.

COVID-19 vaccines have been updated each year since 2022 to improve protection against evolving SARS-CoV-2 variants. However, it is unclear whether a reformulation will be necessary for 2025. KP.2-based monovalent COVID-19 mRNA vaccines (KP.2 MV) were authorized for use in 2024, and they conferred substantial protection against hospitalizations caused by viral variants that emerged and dominated later, such as KP.3.1.1 and XEC. Today, LP.8.1 has become the dominant variant worldwide, particularly so in North America. To characterize the antigenicity of LP.8.1, we tested serial serum samples from 16 individuals who recently received KP.2 MV in neutralization assays against KP.3.1.1, XEC, and LP.8.1 pseudoviruses. Serum neutralizing antibody titers against LP.8.1 were comparable to those against KP.3.1.1 and XEC, indicating that LP.8.1 is antigenically similar to its predecessors. Therefore, the currently authorized KP.2 MV may not need to be updated for 2025, if the vaccine manufacturers could demonstrate comparable immunogenicity for KP.2 MV and LP.8.1-based mRNA vaccines and, of course, in the absence of an antigenically divergent SARS-CoV-2 emerging.