Strong correlations between the binding antibodies against wild type and neutralizing antibodies against omicron BA.1 and BA.2 variants of SARS-CoV-2 in individuals following booster (third dose) vaccination

This study examined the neutralizing activity and receptor binding domain (RBD) antibody levels against wild-type and omicron BA.1 and BA.2 variants in individuals who received three doses of COVID-19 vaccination. The relationship between the SARS-CoV-2 RBD antibody against wild-type and live virus neutralizing antibody titers against omicron BA.1 and BA.2 variants was examined. In total, 310 sera samples from individuals after booster vaccination (third dose) vaccination were tested for specific IgG wild-type SARS-CoV-2 RBD and the omicron BA.1 surrogate virus neutralization test (sVNT). The live virus neutralization assay against omicron BA.1 and BA.2 was performed using the foci-reduction neutralization test (FRNT50). The anti-RBD IgG strongly correlated with FRNT50 titers against BA.1 and BA.2. Non-linear regression showed that anti-RBD IgG with ≥148 BAU/mL and ≥138 BAU/mL were related to detectable FRNT50 titers (≥1:20) against BA.1 and BA.2, respectively. A moderate correlation was observed between the sVNT and FRNT50 titers. At detectable FRNT50 titers (≥1:20), the predicted sVNT for BA.1 and BA.2 were ≥10.57% and ≥11.52%, respectively. The study identified anti-RBD IgG and sVNT levels that predict detectable neutralizing antibodies against omicron variants. Assessment and monitoring of protective immunity support vaccine policies and will help identify optimal timing for booster vaccination.