RESUMO
AbstractO_ST_ABSBackgroundC_ST_ABSThe effectiveness of a 3rd mRNA COVID-19 vaccine ("booster") dose against the omicron (B.1.1.529) variant is uncertain especially in older, high-risk populations. ObjectiveTo determine mRNA booster vaccine effectiveness (VE) against SARS-CoV-2 infection, hospitalization and death in the omicron era by type of booster, type of primary vaccine, time since primary vaccine, age and comorbidity burden. DesignTarget trial emulation study comparing booster vaccination versus no booster. SettingU.S. Department of Veterans Affairs (VA) healthcare system Participants and InterventionAmong persons who had received two mRNA COVID-19 vaccine doses at least 5 months earlier, we designed this retrospective matched cohort study to emulate a target trial of booster mRNA vaccination (BNT162b2 or mRNA-1273) versus no booster, conducted from 12/01/2021 to 03/31/2022. MeasurementsBooster VE. ResultsEach group included 490,838 well-matched persons, predominantly male (88%), mean age 63.0{+/-}14.0 years, followed for up to 121 days (mean 79.8 days). Booster VE >10 days after booster was 42.3% (95% CI 40.6-43.9) against SARS-CoV-2 infection, 53.3% (48.1-58.0) against SARS-CoV-2-related hospitalization and 79.1% (71.2-84.9) against SARS-CoV-2-related death. Booster VE was similar for different booster types (BNT162b2 or mRNA-1273), age groups or primary vaccination regimens, but was significantly higher with longer time since primary vaccination and with higher comorbidity burden. LimitationsPredominantly male population. ConclusionsBooster mRNA vaccination was highly effective in preventing death and moderately effective in preventing infection and hospitalization for up to 4 months after administration in the omicron era. Increased uptake of booster vaccination, which is currently suboptimal, should be pursued to limit the morbidity and mortality of SARS-CoV-2 infection, especially in persons with high comorbidity burden. Primary Funding Source: Department of Veterans Affairs
