The U.S. Centers for Disease Control (CDC) along with researchers from the National Heart, Lung, and Blood Institute and blood collection centers across all 50 states screened over 1.4 million blood donations for infection- and vaccination-induced SARS-CoV-2 from July 2020 to May 2021, before the Delta surge. Approximately 2000 samples were collected monthly from 66 regional areas representing a catchment area of 74% of the U.S. Samples were screened for antibodies to the SARS-CoV-2 spike protein and then for the nucleocapsid protein. Infection-induced positive samples were defined as positive for both spike and nucleocapsid antibodies. Vaccine- and infection-induced seroprevalence varied by age, race, and region. Between July 2020 and May 2021, infection seroprevalence increased from 3.5% to 20.2%. Infection-induced seroprevalence estimates were higher in the Midwest and South compared to the Northeast and West. By May 2021, 83.3% of donations were seropositive from either infection or vaccination. The Northeast had the highest vaccination-induced seroprevalence. Donors aged 65 years and older had the highest combined seroprevalence estimates at 92.2%, and Hispanic donors had the highest infection-induced seroprevalence in May 2021. Because of mild and asymptomatic cases of SARS-CoV-2, the study estimated 2.1 COVID infections per 1 reported CDC case in May 2021. The seroprevalence in blood donors may be higher for vaccination- and lower for infection-induced SARS-CoV-2 than the general U.S. population since blood donors are a select and healthier population.
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