Abstract
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.