{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,25]],"date-time":"2026-09-25T19:25:01Z","timestamp":1790364301265,"version":"4.1.0"},"reference-count":30,"publisher":"Oxford University Press (OUP)","issue":"6","funder":[{"DOI":"10.13039\/100000030","name":"Centers for Disease Control and Prevention","doi-asserted-by":"publisher","award":["75D30120C08170"],"award-info":[{"award-number":["75D30120C08170"]}],"id":[{"id":"10.13039\/100000030","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2025,12,20]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>By the end of 2021 in the United States, spike (S) antibody seroprevalence from coronavirus disease 2019 (COVID-19) vaccination, infection, or both (hybrid immunity) reached over 90%. With high seroprevalence, quantitative antibody concentrations are needed to characterize population immunity. We measured quantitative S antibody concentrations in a national blood donor cohort and evaluated their correlation with protection against infection.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>One blood specimen per quarter in 2022 was tested for quantitative S immunoglobulin G (IgG) and infection-induced (nucleocapsid [N]) total Ig antibodies from a national blood donor cohort of 106 969 people. Median S antibody concentrations were calculated by quarter and by history of vaccination and infection. Among vaccinated donors without N antibodies, protection (measured as 1 minus hazard ratios compared with unvaccinated donors) against N antibody seroconversion was estimated by S antibody concentration. Median S antibody levels were compared using the Kruskal-Wallis tests.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>Median S antibody concentrations increased from 1380 binding antibody units (BAU)\/mL in quarter 1 of 2022 to 1720\u2005BAU\/mL in quarter 4 of 2022. In quarter 4, S antibody levels were lowest in the infection-only group (median, 75\u2005BAU\/mL) and higher in the vaccine-only group (median, 1950\u2005BAU\/mL) and hybrid immunity group (median, 2550\u2005BAU\/mL). Protection against first-time infection increased with higher antibody concentrations; 5010\u2005BAU\/mL (95% confidence interval, 4120\u20136550\u2005BAU\/mL) was associated with 50% protection.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Discussion<\/jats:title>\n                    <jats:p>During 2022, this nationwide study showed mildly increased S IgG concentrations over time among blood donors. Vaccination and hybrid immunity resulted in higher antibody concentrations than infection alone. Higher antibody concentrations were associated with increased protection from infection.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1093\/infdis\/jiaf329","type":"journal-article","created":{"date-parts":[[2025,6,20]],"date-time":"2025-06-20T07:59:29Z","timestamp":1750406369000},"page":"1302-1308","source":"Crossref","is-referenced-by-count":2,"title":["Estimated US Trends in SARS-CoV-2 Spike Antibody Concentrations and Correlation to Risk of First-Time Infections Based on Blood Donations, 2022"],"prefix":"10.1093","volume":"232","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-4974-9058","authenticated-orcid":false,"given":"Jefferson M","family":"Jones","sequence":"first","affiliation":[{"name":"National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention , Atlanta, Georgia ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7046-7245","authenticated-orcid":false,"given":"Eduard","family":"Grebe","sequence":"additional","affiliation":[{"name":"Vitalant Research Institute , San Francisco, California ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Isaac","family":"Lartey","sequence":"additional","affiliation":[{"name":"Westat , Rockville, Maryland ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5619-2767","authenticated-orcid":false,"given":"Mars","family":"Stone","sequence":"additional","affiliation":[{"name":"Vitalant Research Institute , San Francisco, California ,","place":["USA"]},{"name":"Department of Laboratory Medicine, University of California San Francisco , San Francisco, California ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9008-9154","authenticated-orcid":false,"given":"Bryan R","family":"Spencer","sequence":"additional","affiliation":[{"name":"Scientific Affairs, American Red Cross , Gaithersburg, Maryland ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Akitunde","family":"Akinseye","sequence":"additional","affiliation":[{"name":"Westat , Rockville, Maryland ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Irene","family":"Molina Manrique","sequence":"additional","affiliation":[{"name":"Westat , Rockville, Maryland ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3255-4756","authenticated-orcid":false,"given":"Rebecca V","family":"Fink","sequence":"additional","affiliation":[{"name":"Westat , Rockville, Maryland ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Valerie","family":"Green","sequence":"additional","affiliation":[{"name":"Creative Testing Solutions , Tempe, Arizona ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6077-4532","authenticated-orcid":false,"given":"Paula","family":"Saa","sequence":"additional","affiliation":[{"name":"Scientific Affairs, American Red Cross , Gaithersburg, Maryland ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3105-3530","authenticated-orcid":false,"given":"Brad J","family":"Biggerstaff","sequence":"additional","affiliation":[{"name":"National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention , Fort Collins, Colorado ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1843-6251","authenticated-orcid":false,"given":"Melissa M","family":"Coughlin","sequence":"additional","affiliation":[{"name":"National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention , Atlanta, Georgia ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7359-9665","authenticated-orcid":false,"given":"Melissa","family":"Briggs-Hagen","sequence":"additional","affiliation":[{"name":"National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention , Atlanta, Georgia ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marion C","family":"Lanteri","sequence":"additional","affiliation":[{"name":"Department of Laboratory Medicine, University of California San Francisco , San Francisco, California ,","place":["USA"]},{"name":"Creative Testing Solutions , Tempe, Arizona ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9508-5021","authenticated-orcid":false,"given":"Jean","family":"Opsomer","sequence":"additional","affiliation":[{"name":"Westat , Rockville, Maryland ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"David J","family":"Wright","sequence":"additional","affiliation":[{"name":"Westat , Rockville, Maryland ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Michael P","family":"Busch","sequence":"additional","affiliation":[{"name":"Vitalant Research Institute , San Francisco, California ,","place":["USA"]},{"name":"Department of Laboratory Medicine, University of California San Francisco , San Francisco, California 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