S-RBD Antibody Titers Following the First and Second Doses of Inactivated SARS-CoV-2 Vaccination (CoronaVac) in Native Participants: A Prospective Cohort Study in Bali, Indonesia

Abstract

Background: Vaccination has been recognized as an additional option, besides the health protocols practices to control the coronavirus disease 2019 (COVID-19) pandemic, especially with the unknown specific treatment for the disease. This study sought to evaluate the immunogenicity of CoronaVac among the general population in Bali province, a popular tourist spot in Indonesia. Methods: As many as 422 volunteers were recruited from the three vaccination centers, of which 230 volunteers were seronegative and included in the study. CoronaVac was used as vaccine with dose of 0.5 mL or 3 µg at each administration. Blood samples were drawn before vaccination, 21 days after the first dose, and 56 days after second dose, where the interval between the first and second dose vaccination was 28 days. Vaccine immunogenicity was evaluated by the anti-spike receptor-binding domain (anti-S-RBD) IgG titer which was measured using the electrochemiluminescence immunoassay technique. Results: The mean anti-S-RBD levels at 21 days after first dose, and 21 days after the second dose of vaccination are 25.25 ± 59.74 U/mL and 138.77 ± 90.93 U/mL, respectively. The result of the Friedman test was p <0.001 which means that there are significant differences in anti-S-RBD levels between 21 days after first dose and 21 days after second vaccination. Post hoc analysis with the Wilcoxon test also showed significant difference among the three-testing point (p < 0.001). The seroconversion rate from the first dose of CoronaVac was 69.7% and it increased to 99.4% (171/172) on after the second dose. Conclusion: Although the protective level was not totally reached on the first vaccination, the immunogenicity was considered rapid 3 weeks after the first vaccination.