COVID-19 vaccination-induced antibody responses and waning by age and comorbidity status in a large population-based prospective cohort study

Abstract

Background Information on the magnitude and duration of antibody levels after COVID-19 vaccination in different groups may be useful for prioritizing of additional vaccinations. Methods Serum samples were collected every six months in a prospective cohort study among adults in the Netherlands. Geometric mean concentrations (GMCs) of antibodies against the receptor binding domain of the SARS-CoV-2 spike protein were calculated after the primary series, first, and second booster vaccinations. Effects of age (18-59 vs 60-85 years) and medical risk conditions on GMC 2-6 weeks and 21-25 weeks after each vaccination, and on waning during 3-25 weeks after each vaccination, were estimated by linear regression. Results We included 20,816, 16,820 and 5,879 samples collected after primary, first and second booster vaccination, respectively. GMCs at 2-6 and 21-25 weeks after primary series were lower in participants with older age or medical risk conditions. After the first booster, older age was associated with lower GMC at 2-6 weeks, higher GMC at 21-25 weeks, and slower waning. GMCs or waning after the first and second boosters (only 60-85) were not associated with medical risk conditions. Conclusions Since antibody differences by age and medical risk groups have become small with increasing number of doses, other factors such as disease severity rather than antibody levels are useful for prioritization of additional vaccinations.