The relationship between anti-spike SARS-CoV-2 antibody levels and risk of breakthrough COVID-19 among fully vaccinated adults.

The relationship between antibodies to wild-type SARS-CoV-2 antigens and the risk of breakthrough infections is unclear, especially during time periods of Omicron. We investigated the association of anti-spike and anti-receptor binding domain antibody levels and the risk of subsequent breakthrough COVID-19. We included adult paramedics from an observational cohort study who received ≥ 2 mRNA vaccines but did not have COVID-19 before the blood collection. Higher post-vaccine antibody levels to wild-type SARS-CoV-2 antigens were associated with a reduced risk of COVID-19. Further research into clinical utility of antibody levels, to inform a threshold for protection and timing of boosters, should be prioritized.