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Objectives: This study aimed to evaluate the long-term antibody kinetics after vaccinating with an inactivated COVID-19 Vero cell vaccine (CoronaVac) in healthcare workers (HCWs) at a single center in Turkey. Methods: For this prospective observational study, Chemiluminescence immunoassay (CLIA) and enzyme-linked immunosorbent assay (ELISA) were used for the determination of binding antibodies (bAb) and neutralizing antibodies (nAb), respectively. Antibody kinetics were compared for the potential influencing factors, and propensity score analysis was performed to match the subcohort for age. Results: Early bAb and nAb response was achieved in all 343 participants. Titers of bAbs against SARS-CoV-2 on 42 days post-vaccination (dpv) were higher in HCWs who were aged <40 years and who had a history of COVID-19. SARS-CoV-2 bAb levels in HCWs on days 42 (n = 97), 90 (n = 97), and 180 (n = 97) were 175 IU/ml (3.9-250), 107 IU/ml (2.4-250), and 66.1 IU/ml (2.57-250), respectively (p<0.001). SARS-CoV-2 bAb (p<0.001) and nAb (p<0.001) titers decreased significantly over time. There was a high negative correlation between SARS-CoV-2 antibody titers and inverse optic density of nAb responses (Pearson correlation coefficient: -0.738, p<0.001). Conclusions: When the antibody responses were compared, it was seen that the vaccine immunogenicity was better in those who had prior COVID-19 history and were aged <40 years. In the course of time, it was determined that there was a significant decrease in bAb and nAb responses after the 90th day. These results may guide approval decisions for booster COVID-19 vaccines.