On Apr. 27, 2023, a NIAID-led Phase 2 trial compared two Pfizer bivalent mRNA COVID-19 boosters found that while both induced an immune response, neutralizing antibodies were less potent against some of the emerging SARS-CoV-2 variant viruses.

This scenario led the researchers ﾖ part of the Coronavirus Variant Immunologic Landscape Trial, or COVAIL ﾖ to express concern about virus evolution leaving ﾓnot optimalﾔ antibody responses that can be addressed with vaccine strain updates. Their study, published in Clinical Infectious Diseases, called for continuous viral surveillance to assess potential for waning vaccine effectiveness as the virus continues to evolve.