Quantitative SARS-CoV-2 Spike Receptor-Binding Domain on Vaccinated Individuals Compared to Natural Infection

BACKGROUND: Coronavirus disease 2019 (COVID-19) pandemic has been going on for more than 2 years, with various treatments and diagnostic methods available. One of the most prized structures, the receptor-binding domain (RBD) of the spike protein in severe acute respiratory syndrome coronavirus 2 has long been thoroughly researched for its function and becoming the target for various diagnostic methods and treatments, including a vaccine. The spike-RBD (sRBD) antibody count might be the parameter for antibody response in vaccinated and infected individuals. However, no direct comparison is made. AIM: The study aims to compare the sRBD antibody count in the naturally infected individuals to the vaccinated ones. METHODS: We conducted a cross-sectional study with 49 participants of the infected patients, and vaccinated individuals were included in this study from Prof. Dr. R. D. Kandou Hospital, Manado. The participants underwent a COVID-19 antibody test, using enhanced “Chemiluminescence” Immuno assay to analyze the anti-sRBD IgG quantitatively. Results were then analyzed and compared using IBM Statistical Package for Social Sciences ver 25.0 with Mann−Whitney non-parametric test. RESULTS: The study shows a higher median antibody count in the naturally infected group compared to the vaccinated group (132.70 vs. 11.95 U/mL; p < 0.001). Further studies on the topic should be conducted to determine the comparison on a larger scale. CONCLUSION: The s-RBD antibody titer is significantly higher in naturally infected patients than in vaccinated individuals.