Effectiveness of the Coronavirus Disease 2019 (COVID-19) Bivalent Vaccine

ABSTRACT BackgroundThe purpose of this study was to evaluate whether a bivalent COVID-19 vaccine protects against COVID-19. MethodsEmployees of Cleveland Clinic in employment when the bivalent COVID-19 vaccine first became available, were included. Cumulative incidence of COVID-19 over the following 26 weeks was examined. Protection provided by vaccination (analyzed as a time-dependent covariate) was evaluated using Cox proportional hazards regression, with change in dominant circulating lineages over time accounted for by time-dependent coefficients. The analysis was adjusted for the pandemic phase when the last prior COVID-19 episode occurred, and the number of prior vaccine doses. ResultsAmong 51017 employees, COVID-19 occurred in 4424 (8.7%) during the study. In multivariable analysis, the bivalent vaccinated state was associated with lower risk of COVID-19 during the BA.4/5 dominant (HR, .71; 95% C.I., .63-.79) and the BQ dominant (HR, .80; 95% C.I., .69-.94) phases, but decreased risk was not found during the XBB dominant phase (HR, .96; 95% C.I., .82-.1.12). Estimated vaccine effectiveness (VE) was 29% (95% C.I., 21%-37%), 20% (95% C.I., 6%-31%), and 4% (95% C.I., -12%-18%), during the BA.4/5, BQ, and XBB dominant phases, respectively. Risk of COVID-19 also increased with time since most recent prior COVID-19 episode and with the number of vaccine doses previously received. ConclusionsThe bivalent COVID-19 vaccine given to working-aged adults afforded modest protection overall against COVID-19 while the BA.4/5 lineages were the dominant circulating strains, afforded less protection when the BQ lineages were dominant, and effectiveness was not demonstrated when the XBB lineages were dominant. SummaryAmong 51017 working-aged Cleveland Clinic employees, the bivalent COVID-19 vaccine was 29% effective in preventing infection while the BA.4/5 lineages were dominant, and 20% effective while the BQ lineages were. Effectiveness was not demonstrated when the XBB lineages were dominant.