LONGITUDINAL DECLINE OF ANTI-S-RBD IGG ANTIBODY LEVELS AMONG LECTURERS AND EDUCATIONAL STAFF FIVE MONTHS AFTER CORONAVAC VACCINATION IN INDONESIA

Nurmila Sari (Department of Anatomy, Faculty of Medicine, Syarif Hidayatullah State Islamic University, Jakarta, Indonesia)
Yona Mimanda (Department of Clinical Pathology, Faculty of Medicine, Syarif Hidayatullah State Islamic University, Jakarta, Indonesia)
Muniroh (Department of Clinical Pathology, Faculty of Medicine, Syarif Hidayatullah State Islamic University, Jakarta, Indonesia)
Dinnisa Haura Zhafira Hidayat (Department of Medicine, Faculty of Medicine, Syarif Hidayatullah State Islamic University, Jakarta, Indonesia)
Tri Nurjannah (Department of Medicine, Faculty of Medicine, Syarif Hidayatullah State Islamic University, Jakarta, Indonesia)

International Archives of Medical Sciences and Public Health
Vol. 7 No. 1 (2026): International Archives of Medical Sciences and Public Health

Humoral immunity induced by the CoronaVac vaccine may decline overtime. This study assessed changes in anti-spike receptor-binding domain (S-RBD) immunoglobulin G (IgG) antibody levels at 1 month and 5 months after completion of the two-dose CoronaVac regimen. A prospective observational cohort study was conducted among 54 participants, with 28 completing paired antibody measurements. Serum anti-S-RBD IgG concentrations were measured using a chemiluminescence microparticle immunoassay (CMIA), and differences between time points were analyzed using the Wilcoxon signed-rank test. A significant decline in antibody levels was observed, with the median concentration decreasing from 521.1 AU/mL (range: 71.2–2109.4) at 1 month to 57.8 AU/mL (range: 49.0–512.4) at 5 months, representing an approximately 89% reduction (p < 0.001). The Hodges Lehmann estimated median difference was -426.125 AU/mL (95% CI: -633.550 to -260.500). These findings indicate waning humoral immunity within five months after the second CoronaVac dose and support consideration of booster vaccination strategies.