The effectiveness of inactivated SARS-CoV-2 vaccine (CoronaVac) on antibody response in participants aged 65 years and older

In this study, it was aimed to determine the antibody responses after the two doses of inactivated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccinations in people who were above 65 years old and to evaluate the factors affecting this response. A total of 235 participants aged 65 years and older were included. Blood samples were taken and data about age, gender, comorbid diseases, and presence of side effects after vaccination were noted. Anti-SARS-CoV-2 QuantiVac ELISA (IgG) test kit (catalogue number: EI-2606-9601-10-G, Euroimmun) was used. The mean age was 70.38 +/- 4.76. Approximately 120 of 235 participants had at least one comorbid disease. The mean levels of anti-SARS-CoV-2 IgG antibody after 4 weeks from the first and second doses of vaccine were 37.70 +/- 57.08 IU/ml, and 194.61 +/- 174.88 IU/ml, respectively. Additionally, 134 of 235 participants (57.02%) had under 25.6 IU/ml antibody level (negative) after 4 weeks from the first vaccine dose while this rate was 11.48% (n = 27) after 4 weeks from the second vaccine dose. The 19 (70.4%) participants who had under had 25.6 IU/ml antibody level after 4 weeks from the first dose of vaccine had at least one comorbid disease including diabetes mellitus, and 8 (29.6%) participants had no comorbid disease (F = 2.352, p = 0.006). Lower rates of antibody response were detected in participants aged 65 years and older and those with comorbidities both in our study and similar studies in the current literature. Further studies should evaluate whether the low antibody titers are really associated with age and comorbidities or not. Finally, prospective studies are needed to determine how long the immunity provided by SARS-CoV-2 vaccines will continue.