Variability of Immune Response to CoronaVac in the Indonesian Population: A Retrospective Cohort Study in Bantaeng, South Sulawesi,Indonesia

Background: The COVID-19 vaccine, including CoronaVac, is crucial in reducing severe infections and mortality due to COVID-19. However, variability in antibody responses across different populations remains a subject of investigation. This study aimed to evaluate the impact of age and BMI on Immunoglobulin G (IgG) antibody levels three months post-CoronaVac vaccination in a healthy Indonesian cohort. Methods: A retrospective cohort study was conducted on 299 healthy individuals aged 18–70 in Bantaeng, South Sulawesi, Indonesia. IgG levels against the SARS-CoV-2 spike protein receptor-binding domain (RBD) were measured using enzyme-linked immunosorbent assay (ELISA). Blood samples were collected about 90 ± 7 days after the second dose of the vaccine. Baseline IgG levels before vaccination were not measured. However, all participants were confirmed to be immunologically naïve based on the absence of COVID-19 symptoms or infection history. The associations between IgG levels, age, and BMI were analyzed using non-parametric statistical tests. Results: Detectable levels of IgG antibodies were observed three months post-vaccination, with a mean concentration of 4.56 mg/dL. Although the youngest age group (18–35 years) and overweight participants exhibited the highest IgG levels, no significant correlations were observed between IgG levels and age (ρ = –0.042, p = 0.7) or BMI (ρ = 0.043, p = 0.5). Conclusion: IgG responses to CoronaVac were consistent across age and BMI groups, despite expected variation. These findings support its broad use in Indonesia’s diverse population and national vaccination programs. Keywords: Humoral response, COVID-19 vaccines, Inactivated vaccines, Indonesia