Antibody Titers and the Risk of Infection During the SARS-CoV-2 Omicron Phase in Bizen City, Japan.

BACKGROUND

Understanding the association between the immune response and the risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has implications for forthcoming prevention strategies. We evaluated the association between antibody titers and the risk of infection for the general population during the Omicron-dominant phase.

METHODS

This was a prospective cohort study of residents or people affiliated with institutions in Bizen City, which included 1899 participants. We measured the titers of antibodies against SARS-CoV-2 repeatedly every 2 months from June 2022 to March 2023. Infection status was obtained from self-reported questionnaires and the official registry. We estimated risk ratios (RRs) for infection within 2 months of the date of each antibody measurement with 95% confidence intervals (CIs) based on antibody titer categories and spline functions.

RESULTS

Compared with the <2500 arbitrary unit (AU)/mL category, the 2500-5000, 5000-10 000, and ≥10 000 AU/mL categories had adjusted RRs of 0.81 (95% CI, .61-1.08), 0.51 (95% CI, .36-.72), and 0.41 (95% CI, .31-.54), respectively. The spline function showed a nonlinear relationship between antibody titer and risk.

CONCLUSIONS

Higher antibody titers were associated with a lower risk. We demonstrate the usefulness of measuring an antibody titers to determine the appropriate timing for future prevention strategies.