Abstract
Background
Previous SARS-CoV-2 infection and coronavirus disease 2019 (COVID-19) vaccination, independently and combined (“hybrid immunity”), result in partial protection from subsequent infection and strong protection from severe disease. Proportions of the U.S. population that have been infected, vaccinated, or with hybrid immunity remain unclear, posing a challenge for assessing effective pandemic mitigation strategies.
Methods
In this serial cross-sectional study, nationwide blood donor specimens collected during January–December 2021 were tested for spike and nucleocapsid antibodies, and donor COVID-19 vaccination history of ≥1 dose was collected. Monthly seroprevalence induced from SARS-CoV-2 infection, COVID-19 vaccination, or both, were estimated. Estimates were weighted to account for demographic differences from the general population, and were compared temporally and by demographic factors.
Results
Overall, 1,123,855 blood samples were assayed. From January to December 2021, the weighted percentage of donations with seropositivity due to: vaccination without previous infection increased from 3.5% (95% CI, 3.4%-3.7%) to 64.0%, (95% CI, 63.5%-64.5%); previous infection without vaccination decreased from 15.6% (95% CI, 15.2%-16.0%) to 11.7% (95% CI, 11.4%-12.0%); hybrid immunity increased from 0.7% (95% CI, 0.6%-0.7%) to 18.9% (95% CI, 18.5%-19.3%); and from infection, vaccination, or both increased from 19.8% (95% CI (19.3-20.2) to 94.5% (95% CI, 93.5%-94.0% 0.1%). Infection- and vaccination-induced antibody responses varied significantly by age, race-ethnicity, and region, but not by gender.
Conclusions
Our results indicate substantial increases in population humoral immunity from SARS-CoV-2 infection, COVID-19 vaccination, and hybrid immunity during 2021. These findings are important to consider in future COVID-19 studies and long-term pandemic mitigation efforts.
Keywords: SARS-CoV-2, seroprevalence, antibodies, vaccination, immunity
Contributor Information
Michael P. Busch, Vitalant Research Institute, San Francisco, California, USA University of California San Francisco, San Francisco, California, USA.
Susan L. Stramer, American Red Cross, Scientific Affairs, Gaithersburg and Rockville, Maryland, USA
Mars Stone, Vitalant Research Institute, San Francisco, California, USA; University of California San Francisco, San Francisco, California, USA.
Elaine A. Yu, Vitalant Research Institute, San Francisco, California, USA University of California San Francisco, San Francisco, California, USA.
Eduard Grebe, Vitalant Research Institute, San Francisco, California, USA; University of California San Francisco, San Francisco, California, USA.
Edward Notari, American Red Cross, Scientific Affairs, Gaithersburg and Rockville, Maryland, USA.
Paula Saa, American Red Cross, Scientific Affairs, Gaithersburg and Rockville, Maryland, USA.
Robyn Ferg, Westat, Rockville, Maryland, USA.
Irene Molina Manrique, Westat, Rockville, Maryland, USA.
Natalia Weil, Westat, Rockville, Maryland, USA.
Rebecca V. Fink, Westat, Rockville, Maryland, USA
Matt Levy, Westat, Rockville, Maryland, USA.
Valerie Green, Creative Testing Solutions, Tempe, Arizona, USA.
Sherri Cyrus, Creative Testing Solutions, Tempe, Arizona, USA.
Phillip C. Williamson, Creative Testing Solutions, Tempe, Arizona, USA
James Haynes, American Red Cross, Scientific Affairs, Gaithersburg and Rockville, Maryland, USA.
Jamel Groves, American Red Cross, Scientific Affairs, Gaithersburg and Rockville, Maryland, USA.
David Krysztof, American Red Cross, Scientific Affairs, Gaithersburg and Rockville, Maryland, USA.
Brian Custer, Vitalant Research Institute, San Francisco, California, USA; University of California San Francisco, San Francisco, California, USA.
Steve Kleinman, Vitalant Research Institute, San Francisco, California, USA.
Brad J. Biggerstaff, Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
Jean D. Opsomer, Westat, Rockville, Maryland, USA
Jefferson M. Jones, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
Supplementary Material
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.