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Published on: August 12, 2021
Estimated US Trends in SARS-CoV-2 Spike Antibody Concentrations and Correlation to Risk of First-Time Infections
J M Jones1, E Grebe2, I Lartey3
1National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
Background:
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.
Methods:
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.
Results:
Median S antibody concentrations increased from 1380 binding antibody units (BAU)/mL in quarter 1 of 2022 to 1720 BAU/mL in quarter 4 of 2022. In quarter 4, S antibody levels were lowest in the infection-only group (median, 75 BAU/mL) and higher in the vaccine-only group (median, 1950 BAU/mL) and hybrid immunity group (median, 2550 BAU/mL). Protection against first-time infection increased with higher antibody concentrations; 5010 BAU/mL (95% confidence interval, 4120-6550 BAU/mL) was associated with 50% protection.
Discussion:
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.
