Correlation between Anti-S1 RBD IgG Titer and neutralizing antibodies against SARS-CoV-2 After Heterologous booster immunization Ulfi Rahma Efrianti (a), Beti Ernawati Dewi (b,c*), Tjahjani Mirawati Sudiro (c)
a) Master^s Programme in Biomedical Science, Faculty of Medicine, Universitas Indonesia
b) Infectious Disease and Immunology Cluster, Indonesian Medical Education and Research Institute, Indonesia
c) Department of Microbiology, Faculty of Medicine, Universitas Indonesia-Cipto Mangunkusumo Hospital
Abstract
Antibodies produced by plasma cells in response to the COVID-19 vaccine can be neutralizing and non-neutralizing antibodies. Neutralizing antibodies (nAbs) are important for protection against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection. The gold standard for measuring levels of neutralizing antibodies via Plaque Reduction Neutralization Test (PRNT) requiring live pathogen and a Biosafety Level 3 (BSL3) facilities. This study aimed to determine the correlation between Anti-S1 RBD IgG titer and nAbs SARS-CoV-2 in vaccinated subjects. A cross-sectional study was conducted in 20 plasma samples immunized with a primary series of two doses and 36 plasma samples from individuals after booster vaccination (third dose). Anti-S1 RBD IgG titer were determined using indirect ELISA assay. Measure the %inhibition of neutralizing antibody measured by sVNT. The relationship between the Anti-S1 RBD IgG and Neutralizing antibodies were analyzed using Spearman^s correlation coefficient. IgG anti-S1 RBD titer and nAbs decreased with time in a similar pattern. At 24-28 weeks after the 2nd vaccination showed a 60% decrease in antibody titers and a 40% reduction in nAbs. Through Spearman^s correlation, we found correlations between IgG Anti-S1 RBD and the percentage of inhibition of nAbs, after 2nd vaccination (r = 0.720, p-value < 0.0001) and after 3rd vaccination (r = 0.821, p-value < 0.0001)
