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Introduction: This study aimed to evaluate the long-term effectiveness of COVID-19 vaccination in healthcare workers by analyzing the population's response to the vaccine after two years, based on anti-SARS-CoV-2 protein S antibody levels. Additionally, the study aimed to assess the impact of basic factors on antibody levels., Material and Methods: A total of 4,090 healthcare workers were included in the study, and their antibody levels were measured using ELISA to detect anti-SARS-CoV-2 immunoglobulin G (IgG). Statistical analysis was conducted to examine the influence of COVID-19 infection, vaccination status, and number of vaccine doses on antibody concentrations., Results and Conclusion: The majority of participants (85.1%) received the Pfizer/BioNTech vaccine, while a smaller percentage chose vector vaccines such as AstraZeneca and Johnson & Johnson. The incidence of COVID-19 among vaccinated individuals was relatively low for all vaccines, confirming their effectiveness in preventing symptomatic SARS-CoV-2 infection. The study observed variations in IgG antibody levels within the study population, with only 0.46% of individuals testing negative for the presence of antibodies. The average anti-SARS-CoV-2 IgG values showed significant differences across consecutive 3-month periods following infection or vaccination, with a gradual decrease over time. Notably, the most significant changes in antibody levels were observed within the first 6 months (mean values ranged from 3647.11 BAU/ml to 2601.49 BAU/ml). Subsequently, minor fluctuations were observed, with mean antibody values hovering around 2000 BAU/ml. The differences between average anti-SARS-CoV-2 IgG values between consecutive 3-month periods from disease onset were statistically significant., Competing Interests: The authors declare no conflict of interest., (Copyright © 2023 Termedia.)