COVID-19 vaccine effectiveness against SARS-CoV-2 infection in the United States prior to the Delta and Omicron-associated surges: a retrospective cohort study of repeat blood donors (preprint)

To inform public health policy, it is critical to monitor COVID-19 vaccine effectiveness (VE), including against acquiring infection. We estimated VE using a retrospective cohort study among repeat blood donors who donated during the first half of 2021, demonstrating a viable approach for monitoring of VE via serological surveillance. Using Poisson regression, we estimated overall VE was 88.8% (95% CI: 86.2-91.1), adjusted for demographic covariates and variable baseline risk. Time since first reporting vaccination, age, race-ethnicity, region, and calendar time were statistically significant predictors of incident infection. Studies of VE during periods of Delta and Omicron spread are underway.

COVID-19 vaccine effectiveness against SARS-CoV-2 infection in the United States prior to the Delta and Omicron-associated surges: a retrospective cohort study of repeat blood donors (preprint)

To inform public health policy, it is critical to monitor COVID-19 vaccine effectiveness (VE), including against acquiring infection. We estimated VE using a retrospective cohort study among repeat blood donors who donated during the first half of 2021, demonstrating a viable approach for monitoring of VE via serological surveillance. Using Poisson regression, we estimated overall VE was 88.8% (95% CI: 86.2–91.1), adjusted for demographic covariates and variable baseline risk. Time since first reporting vaccination, age, race-ethnicity, region, and calendar time were statistically significant predictors of incident infection. Studies of VE during periods of Delta and Omicron spread are underway.

Seroprevalence of Antibodies to SARS-CoV-2 in US Blood Donors (preprint)

Background To identify blood donors eligible to donate Coronavirus Disease-2019 (COVID-19) Convalescent Plasma (CCP), a large blood center began testing for antibodies to SARS-CoV-2, the etiologic agent of COVID-19. We report the seroprevalence of total immunoglobulin directed against the S1 spike protein of SARS-CoV-2 in US blood donors. Methods Unique non-CCP donor sera from June 1-July 31, 2020 were tested with the Ortho VITROS Anti-SARS-CoV-2 total immunoglobulin assay (positive: signal-to-cutoff (S/C) =>1). Donor age, sex, race/ethnicity, ABO/RhD, education, and experience were compared to June and July 2019. Multivariate regressions were conducted to identify demographics associated with the presence of antibodies and with S/C values. Results Unique donors (n=252,882) showed an overall seroprevalence of 1.83% in June (1.37%) and July (2.26%), with the highest prevalence in northern New Jersey (7.3%). In a subset of donors with demographic information (n=189,565), higher odds of antibody reactivity were associated with non-Hispanic Native American/Alaskan (NH-NAA/A) and Black (NH-B), and Hispanic (H) race/ethnicity, age 18-64, middle school or lesser education, blood Group A, and never or non-recent donor status. In positive donors (n=2,831), antibody signal was associated with male sex, race/ethnicity (NH-NAA/A, NH-B and H) and geographic location. Conclusions Seroprevalence remains low in US blood donors but varies significantly by region. Temporal trends in reactivity may be used to gauge the effectiveness of public health measures. Before generalizing these data from healthy donors to the general population however, rates must be corrected for false positive test results among low prevalence test subjects and adjusted to match the wider demography.