Anti-SARS-CoV-2 spike receptor binding domain (S-RBD) IgG antibodies following CoronaVac administration: a longitudinal study. Anti-SARS-CoV-2 S-RBD IgG antibodies

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Reports on antibody titers following CoronaVac administration are still scarce, particularly when it comes to the post-vaccination effectiveness of CoronaVac in the Indonesian population. The purpose of this study is to determine the efficacy of COVID-19 vaccination by comparing the IgG levels against the S1 subunit of SARS-CoV-2 RBD after the first and second vaccinations. The researchers collected venous blood samples from participants after they received the CoronaVac 600 SU/0.5 mL vaccine at two different intervals (14 days and 28 days). Blood was drawn twice (after the first and second vaccinations) and tested for antibodies (positive antibody detection value of 50 AU/mL). Paired data were analyzed by using either the Wilcoxon test (numerical) or the McNemar test (categorical). The median IgG1 levels in the 14-day interval between vaccine doses were 64.40 AU/mL and IgG2 levels were 886.10 AU/mL. Meanwhile, the median IgG1 level was 146.10, and IgG2 level was 688.00.AU/mL in the group with a 28-day interval between vaccine doses. After the first vaccination, 60.00 % of study subjects had positive IgG levels, which increased to 98.57% after the second vaccination. Following the full-dose vaccination, all participants had higher antibody levels, and considered significant. The effect was stronger in the group that received the vaccine at 14-day intervals. CoronaVac has also been shown to increase the prevalence of detectable antibody positivity in study participants.