Objectives The influential factors for anti-severe acute respiratory syndrome coronavirus 2 spike protein antibody (S-ab) levels were assessed after the administration of BNT162b2 mRNA coronavirus disease-2019 (COVID-19) vaccine at short and medium terms.

Methods A total of 470 healthcare workers (118 males, mean age 41.0±11.9 years) underwent serum S-ab level measurement at 3 and 8 months after two inoculations of BNT162b2 vaccine given 3 weeks apart, who had no history of COVID-19 were enrolled in this study. The changes and differences after vaccination due to gender and adverse reactions of S-ab were analyzed.

Results Systemic adverse reactions incidence (48%) was significantly higher after the second dose than after the first dose (8%). S-ab levels decreased as the age increased (from the 20s to 60s) in both measurements. S-ab level 8 months after the second inoculation (median 476.3 [interquartile range {IQR} 322.4-750.6] U/mL) was significantly lower than that after 3 months (977.5 [637.2-1409.0] U/mL; P <0.001). The median decrease rate of S-ab levels in 5 months was 50.3 (IQR 40.3-62.6) % and those differences were not observed among all generations. Gender-associated differences in S-ab levels were not observed; however, a significant relationship between higher S-ab levels and the systemic adverse reactions was observed at both measurements.

Conclusions The systemic adverse reaction is an independent factor for higher S-ab levels at short and medium terms after BNT162b2 vaccination as demonstrated in our data.