Abstract
Objective: This study aimed to evaluate the immunogenicity of the BNT162b2 mRNA vaccine up to 180 days after
the third dose in Japanese healthcare workers.
Methods: From April 2021 to July 2022, 100 participants (median age: 39 years; interquartile range: 30-48) received
at least two doses of the BNT162b2 vaccine, with 90 participants having a third dose. Baseline blood samples were
collected before the first-dose and up to 180 days after the final dose. Anti-S-IgG antibody levels were measured using the Abbott and Fujirebio assays.
Results: Of all participants, 76 who had no SARS-CoV-2 infection, were not on immunosuppressants, and provided
timely blood samples after receiving their third dose were included in the primary analysis. The S-IgG level exhibited
bimodal peaks at 14 days after the second and third doses, followed by a steady decline. Antibody titers at 90
and 180 days after the third dose were higher than those at 90 and 180 days after the initial dose.
Conclusions: The third dose of the BNT162b2 vaccine was associated with an increase in anti-S-IgG antibody levels
up to 180 days post-vaccination, suggesting the value of multiple booster doses of COVID-19 vaccines.
