Anti‐spike protein IgG antibody responses up to 3 months after the third dose of the BNT162b2 mRNA vaccine in medical care workers

Background This study aimed to assess the changes in anti‐spike protein IgG antibody titer over time following mRNA vaccination (BNT162b2) against severe acute respiratory syndrome coronavirus 2. Methods We monitored IgG levels in 23 medical care workers (MCWs) for up to 3 months after administering the third dose of BNT162b2. Blood samples were periodically collected from all participants. Results Following the third dose, the median antibody titer increased to 252 and 327% compared with antibody levels at 1 and 3 months after the second dose, respectively. Additionally, compared with 1 month after the second dose, the median antibody titer decreased to 30.2 and 9.8% at 3 and 6 months, respectively, and to 39.1% at 3 months, compared with 1 month after the third dose. Conclusion Antibody levels declined quickly after the second dose but declined more slowly after the third dose, showing a booster effect. This study provides insights into the immunogenicity of booster doses and time intervals for booster vaccination strategies.