Waning of humoral immunity and affecting factors after BNT162b2 vaccination: a cohort study with latent growth curve model in Fukushima

Measuring long-term antibody titer kinetics and subsequent COVID-19 vaccinations are crucial for identifying vulnerable populations. Our aim was to determine the association between long-term antibody kinetics up to seven months post second vaccination, including peak titers and factors. A three-time survey was performed in 2021 on healthcare workers in Japan to investigate the changes in humoral immunity using chemiluminescence immunoassay. We included participants who completed the second-dose vaccination, the antibody survey for all three terms, and those who were not infected with COVID-19. A latent growth curve model was used to identify the factors affecting the peak titer and decreasing the antibody slope. Overall, 205 eligible participants were included in the final analysis. Of these, the mean titers of immunoglobulin G (IgG) against the spike (S) protein and the neutralizing activity at seven months after the second vaccination decreased to 154.3 AU/ml (8.8% of the peak titer) and 62.1 AU/ml (9.5% of the peak titer), respectively. The growth model of IgG showed that age significantly affected peak titers (p < 0.001); however, a significant difference was not found for the decreasing slope. In conclusion, aging adults had significantly lower peak antibody titers, however age did not relate to decreasing slope.