Nearly All American Blood Donors Have COVID-19 Antibodies

The percentage of American blood donors with COVID-19 antibodies increased to 96.4% by September 2022, according to findings published Friday in CDC’s Morbidity and Mortality Weekly Report. The percentage of blood donors with hybrid immunity derived from both previous infection and vaccination increased to 47.7%.

Since July 2020, CDC has used blood donations to estimate COVID-19 seroprevalence in the United States. In this study, a team of investigators led by Vitalant Research Institute and supported by the American Red Cross, Creative Testing Solutions and Westat tested blood samples from a nationwide, longitudinal cohort of 142,000 repeat blood donors (72,748 of these blood donors who donated and were tested in all four analysis periods were included in this analysis) to estimate the prevalence of infection- or vaccination-induced or hybrid antibodies during four 3-month periods (April–June 2021, January–March 2022, April–June 2022 and July–September 2022).

Between April and June 2021, an estimated 68.4% of blood donors had SARS-CoV-2 antibodies from previous infection or vaccination, including 47.5% from vaccination alone, 12% from infection alone and 8.9% with hybrid immunity. By April 2022, 93.5% of blood donors had COVID-19 antibodies, with an estimated 39% from vaccination alone, 20.5% from infection alone and 34.1% from both. During the study’s final period, 96.4% of donors had COVID-19 antibodies, with 26.1% from vaccination alone, 22.6% from infection alone and 47.7% from both.

The study also estimated antibody prevalence by vaccination status, age and race. By September 2022, the prevalence of infection-induced immunity was 85.7% among unvaccinated persons and 64.3% among vaccinated persons. During the same timeframe, donors over the age of 65 had the lowest prevalence of hybrid immunity (36.9%) while adolescents and young adults (16–29 years old) had the highest prevalence (59.6%). During all periods, investigators observed higher prevalences of hybrid immunity among Black and Hispanic populations than among White and Asian populations.

According to investigators, the increase in seroprevalence during the study period, including hybrid immunity, likely contributed to lower rates of severe disease and death from COVID-19 in 2022–23 than during the early pandemic. Furthermore, they believe that low prevalence of infection-induced and hybrid immunity among older adults reflects the success of public health infection prevention efforts. Because older adults have consistently had a higher risk for severe disease compared with younger age groups, the findings underscore the importance this group staying up to date with recommended COVID-19 vaccination.

This CDC-funded program is ongoing, and future publications will detail the rates and clinical outcomes if vaccine breakthrough infections and reinfections compared to first infections in non-vaccinated persons, the changes in spike IgG antibody levels in the cohort over time, and the associations of spike IgG antibodies to neutralizing antibodies and risk of vaccine breakthrough infections and reinfections and consequent disease.