Abstract
We examined the association between antibody titer levels and risk of coronavirus disease 2019 (COVID-19) infection in the general Japanese population, including a total of 1,972 participants between June and September 2022. Specifically, we ascertained participantsIgG antibody titers targeting the spike protein and infection status, and subsequently examined the association between antibody titer categories (< 2,500, 2,500-5,000, 5,000-10,000 and > 10,000 AU/mL) and COVID-19 infection to estimate risk ratios (RR) and their 95% confidence intervals (CI). Compared to the lowest category, the adjusted RR for participants with antibody titers ≥ 10,000 AU/mL was 0.38 (95% CI: 0.20-0.71). The observed non-linear relationship between the titers and the risk of infection showed that the risk decreased as the participant's antibody titer increased, but the slope became milder when the antibody titer reached approximately 10,000 AU/mL. These findings may contribute to the use of an individual's antibody titer to consider appropriate timing of vaccination.