Abstract
Objectives: This study aims to evaluate the effectiveness of the inactivated SARS-COV-2 vaccine (Sinovac-CoronaVac), first administered to healthcare professionals in Turkey on January 14, 2021.<br>Methods: Healthcare professionals without a history of COVID-19, PCR test positivity, or chronic disease were included in the study. The antibody levels for S1 RBD antigen were measured with the Siemens SARS-CoV-2 IgG (sCOVG) kit one month and six months after the two-dose CoronaVac vaccine.<br>Results: A total of 108 health professionals, 35 women and 73 men, were included in this study. The mean age of the participants was 37.5 ± 10.7 years. A total of 103 (95.3%) individuals had positive antibody values, and five (4.6%) had negative values after the second vaccination. After the second vaccine dose, 11 (10.1%) participants were diagnosed with COVID-19. There was a significant decrease in antibody values in the sixth month compared to the first month (p <0.001). The first-month measurements showed a significant negative correlation between age and antibody levels. Likewise, there were no significant differences in antibody levels between men and women in the first and sixth months. However, there was a significant difference in antibody levels in the first month for occupational groups (p=0.015). The nurses ' antibody levels in the first month were significantly higher than the doctors (p=0.05).<br>Conclusion: Although the antibody level of the CoronaVac vaccine decreased significantly for the first six months, the infection was mild in 10 % of the participants. Large-scale studies are needed for the protectiveness of vaccines and the prevention of COVID-19. J Microbiol Infect Dis 2022; 12(4):154-159.

Key words: COVID-19, healthcare professionals, vaccination