• Jefferson M Jones, Mars Stone, Hasan Sulaeman, Rebecca V Fink, Honey Dave, Matthew E Levy, Clara Di Germanio, Valerie Green, Edward Notari, Paula Saa, Brad J Biggerstaff, Donna Strauss, Debra Kessler, Ralph Vassallo, Rita Reik, Susan Rossmann, Mark Destree, Kim-Anh Nguyen, Merlyn Sayers, Chris Lough, Daniel W Bougie, Megan Ritter, Gerardo Latoni, Billy Weales, Stacy Sime, Jed Gorlin, Nicole E Brown, Carolyn V Gould, Kevin Berney, Tina J Benoit, Maureen J Miller, Dane Freeman, Deeksha Kartik, Alicia M Fry, Eduardo Azziz-Baumgartner, Aron J Hall, Adam MacNeil, Adi V Gundlapalli, Sridhar V Basavaraju, Susan I Gerber, Monica E Patton, Brian Custer, Phillip Williamson, Graham Simmons, Natalie J Thornburg, Steven Kleinman, Susan L Stramer, Jean Opsomer, and Michael P Busch.
• COVID-19 Response Team, Centers for Disease Control and Prevention, Atlanta, Georgia.
• JAMA. 2021 Oct 12; 326 (14): 1400-1409.

ImportancePeople who have been infected with or vaccinated against SARS-CoV-2 have reduced risk of subsequent infection, but the proportion of people in the US with SARS-CoV-2 antibodies from infection or vaccination is uncertain.ObjectiveTo estimate trends in SARS-CoV-2 seroprevalence related to infection and vaccination in the US population.Design, Setting, And ParticipantsIn a repeated cross-sectional study conducted each month during July 2020 through May 2021, 17 blood collection organizations with blood donations from all 50 US states; Washington, DC; and Puerto Rico were organized into 66 study-specific regions, representing a catchment of 74% of the US population. For each study region, specimens from a median of approximately 2000 blood donors were selected and tested each month; a total of 1 594 363 specimens were initially selected and tested. The final date of blood donation collection was May 31, 2021.ExposureCalendar time.Main Outcomes And MeasuresProportion of persons with detectable SARS-CoV-2 spike and nucleocapsid antibodies. Seroprevalence was weighted for demographic differences between the blood donor sample and general population. Infection-induced seroprevalence was defined as the prevalence of the population with both spike and nucleocapsid antibodies. Combined infection- and vaccination-induced seroprevalence was defined as the prevalence of the population with spike antibodies. The seroprevalence estimates were compared with cumulative COVID-19 case report incidence rates.ResultsAmong 1 443 519 specimens included, 733 052 (50.8%) were from women, 174 842 (12.1%) were from persons aged 16 to 29 years, 292 258 (20.2%) were from persons aged 65 years and older, 36 654 (2.5%) were from non-Hispanic Black persons, and 88 773 (6.1%) were from Hispanic persons. The overall infection-induced SARS-CoV-2 seroprevalence estimate increased from 3.5% (95% CI, 3.2%-3.8%) in July 2020 to 20.2% (95% CI, 19.9%-20.6%) in May 2021; the combined infection- and vaccination-induced seroprevalence estimate in May 2021 was 83.3% (95% CI, 82.9%-83.7%). By May 2021, 2.1 SARS-CoV-2 infections (95% CI, 2.0-2.1) per reported COVID-19 case were estimated to have occurred.Conclusions And RelevanceBased on a sample of blood donations in the US from July 2020 through May 2021, vaccine- and infection-induced SARS-CoV-2 seroprevalence increased over time and varied by age, race and ethnicity, and geographic region. Despite weighting to adjust for demographic differences, these findings from a national sample of blood donors may not be representative of the entire US population.

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