Waning of Anti-SARS-CoV-2 Spike Antibody Levels 100 to 200 Days after the Second Dose of the BNT162b2 Vaccine.

Anti-SARS-CoV-2 antibodies of 444 vaccinated hospital employees in Japan were measured 94-109 days and 199-212 days after receiving the second BNT162b2 vaccine dose to evaluate the intensity and duration of antibody response in our own cohort. Among uninfected participants, anti-S antibody levels were greatly decreased 199-212 days after the second vaccination compared to the levels measured 94-109 days after the second vaccination (median levels: 830 AU/mL and 2425 AU/mL, respectively; < 0.001). The rate of decrease between the two testing periods was lower in infected participants than in uninfected participants (median: 47.7% and 33.9%, respectively; < 0.001). Anti-S antibody levels were significantly higher in females (median: females, 2546 AU/mL; males, 2041 AU/mL; = 0.002 during the first test period). The peak body temperature after vaccination was higher in females than in males (median: females, 37.4 °C; males: 37.1 °C; = 0.044). Older males tended to have lower antibody levels. In conclusion, the duration of the anti-S antibody response to the BNT162b2 vaccine was short-lived, particularly in males. Anti-S antibody levels of 1000 AU/mL or lower according to SARS-CoV-2 IgG II Quant (Abbott) might indicate insufficient prevention against the delta variant, and the majority of participants appeared to have lost their protection 200 days after vaccination.