ABSTRACT
Background: More than a year has passed since the first coronavirus vaccines were widely used. However, some healthcare workers are infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) despite full vaccination. The immune effect of SARSCoV- 2 vaccines attenuates in a few months in contrast to other universal vaccines, such as the hepatitis B vaccine, which have an immune effect that lasts for a longer time. In addition, the neutralizing antibody (Ab) titers can be measured only in limited medical institutions. In this study, we aimed to investigate the factors that predict SARS-CoV-2 infection in healthcare workers after vaccination. Method(s): In this study, we enrolled one thousand one hundred and thirty-three healthcare workers (826 women, 307 men) after second inoculation of the BNT162b2 vaccine (Pfizer /BioNTech) in February- April 2021. Medical checkups and self-reported questionnaires were used to collect medical histories and demographic characteristics. The Alinity SARS-CoV-2 IgG II Quant (Abbott) quantitative IgG spike protein serology assay was examined in a cohort of participants 1, 4, 6 months after the second vaccination, and 1 month after the third vaccination of the BNT162b vaccine. Lower Ab titers were defined under median at each time point. The relationships between SARS-CoV-2 infection and these factors were analyzed. Result(s): The mean observation period was four hundred and fortyeight days. The median titers at 1, 4, 6 months after the second vaccination were 9293 U/mL (interquartile range [IQR], 5840-14392 U/mL), 1658 U/mL (IQR, 999-2676) and 832 U/mL (IQR, 523-1300), respectively. The risk factors for lower Ab titers were age (60 years older, odds ratio [OR], 2.08), presence of current illness (OR 1.52), smoking habit (OR 2.36), and no fever after the second vaccination (OR 2.44). The median titers at 1 month after the third vaccination was 13780 U/mL (IQR, 9085-22722), and the risk factor for lower Ab titers was hepatitis B surface Ab (HBsAb) negative (OR 1.38). The total 1-year cumulative infection rate was 4.9%. The median infection period was three hundred and twenty days (IQR, 298-365) after the second vaccination. The risk factors of infection were age (30 s and 40 s), and HBsAb negative. The 1-year cumulative infection rate of 30-40 s and other ages were 6.6% and 3.7%, respectively (p<0.01). The 1-year cumulative infection rate of HBsAb negative participants with 30-40 s and other age were 7.7% and 4.9%, respectively (p = 0.064), while that of HBsAb positive participants with 30-40 s and other age were 6.7% and 1.7%, respectively (p<0.01). Conclusion(s): HBsAb and age can become prognostic factors to be infected with SARS-CoV-2 after vaccination. Especially, HBsAb negative people under 50 years old should pay attention to SARSCoV- 2 infection even after second vaccination.