Coronavirus Disease 2019 Vaccine Effectiveness Against Severe Acute Respiratory Syndrome Coronavirus 2 Infection in the United States Before the Delta- and Omicron-Associated Surges: A Retrospective Cohort Study of Repeat Blood Donors

BackgroundTo inform public health policy, it is critical to monitor coronavirus disease 2019 vaccine effectiveness (VE), including against acquiring infection.MethodsWe estimated VE using self-reported vaccination in a retrospective cohort of repeat blood donors who donated during the first half of 2021, and we demonstrated a viable approach for monitoring VE via serological surveillance.ResultsUsing Poisson regression, we estimated an overall VE of 88.8% (95% confidence interval, 86.2-91.1), adjusted for demographic covariates and variable baseline risk.ConclusionsThe time since first reporting vaccination, age, race and/or ethnicity, region, and calendar time were statistically significant predictors of incident infection