ABSTRACT
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 (637.2-1,409.0) 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.