Changes in Antibody Titer over Time after Vaccination with SARS-CoV-2 Vaccine (BNT162b2)

Abstract

We investigated changes in antibody titers among staff members of a target hospital who had received the BNT162b2 vaccine. Blood samples were collected from 176 of the 599 staff members who received the first vaccination at the hospital, and antibody titers were measured using the CLEIA method. The mean antibody titer (standard deviation) immediately before the third vaccination was 17.5 u/mL (14.58), and that two weeks after the second vaccination was 233.6 u/mL (161.49), indicating a 13.2-fold increase. However, the mean antibody titer (standard deviation) immediately before the third vaccination was 15.3 m/uL (21.50), which was lower than that immediately before the second vaccination. These results indicated that antibody titers decreased with the passage of time after vaccination, similar to the findings of previous studies in Japan and overseas. Although individual differences in antibody titers were found in this study, we did not investigate factors that might affect antibody titers, such as the participant's underlying disease, lifestyle, and degree of adverse reactions following vaccination. The influence of these factors is a subject for future study.