ABSTRACT
Studies evaluating the levels of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) anti-spike protein receptor-binding domain (S-RBD) immunoglobulin G (IgG) antibodies in vaccinated healthcare workers in Indonesia are limited. Objectives: Evaluating time-dependent levels of anti-IgG S-RBD antibodies and monitoring the response of healthcare workers in a tertiary hospital in Indonesia after vaccination. Materials and methods: This prospective cohort observational study was conducted from January to December 2021. A total of 50 healthcare workers participated in the study. Blood samples were collected at five time points. Antibody levels were measured using a CL 1000i analyzer (Mindray Bio-Medical Electronics Co., Ltd., Shenzhen, China). Antibody levels between groups were analyzed using the Wilcoxon signed-rank test with P less than 0.05. Results: The median levels of SARS-CoV-2 anti-S-RBD IgG antibody on days 14, 28, 90, and 180 were significantly higher than the levels on day 0 (P<0.001). After the second dose, peak levels were observed on day 14; the levels decreased gradually after day 28. Despite receiving two doses of the vaccine, 10 out of 50 participants (20%) were infected with COVID-19 (coronavirus disease 2019). However, symptoms were mild, and antibody levels were significantly higher than in noninfected participants (P<0.001). Conclusion: SARS-CoV-2 anti-S-RBD IgG antibody levels increased significantly until day 14 after the second dose; the levels decreased gradually after day 28. Ten participants (20%) were infected with SARS-CoV-2, with mild symptoms.