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

Background: To inform public health policy, it is critical to monitor coronavirus disease 2019 vaccine effectiveness (VE), including against acquiring infection.

Methods: We 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.

Results: Using 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.

Conclusions: The time since first reporting vaccination, age, race and/or ethnicity, region, and calendar time were statistically significant predictors of incident infection.