Neutralization-activity of Sera/IgG Obtained from Fully BNT162b2- Vaccinated Individuals Against 10 Clinical SARS-CoV-2 isolates Including Various VOCs (Alpha/Beta/Gamma/Delta) and VUM (Kappa)

Abstract In the present prospective study, 225 individuals in Kumamoto General Hospital, Japan, who received two-doses of BNT162b2 vaccine were enrolled/followed up over 150 days. Neutralizing activity (NT50) of sera on day-60 post-1st -dose against wild-type (SARS-CoV-2Wuhan)(n = 211) and 9 variants (VOCs; Alpha/Beta/Gamma/Delta, and VUM; Kappa)(n = 45) were examined. Also, antiviral activity (EC50) of IgG obtained from day-60 sera against SARS-CoV-2Wuhan and 9 variants were evaluated (n = 45). Finally, time-dependent alterations of IgG-activity (n = 25) against SARS-CoV-2Wuhan/variants were examined. Day-60 sera showed reduced NT50 by more than 50% against all variants, and greatest reduction was seen with Beta. IgG of high-responders (IgGhighs) and moderate-responders (IgGmoderates) showed similar fold-changes in EC50 against each variant compared to SARS-CoV-2Wuhan. However, absolute EC50 of IgGhighs were 2 ~ 3-folds greater than those of IgGmoderates against all SARS-CoV-2s. Evaluation of EC50 of IgG obtained at different time-points (day-28 to -150) revealed time-dependent reduction of IgG-activity against various VOCs/VUM. However, against Delta, relatively long-lasting favorable EC50 (at least 150 days) of both IgG were observed. Our data strongly suggest that rapid expansion of vaccine administration in Japan was remarkably effective to repress SARS-CoV-2 pandemic with the spread of Delta, and give insights in better understanding of the antiviral-efficacy of SARS-CoV-2 vaccine and vaccine-elicited immune-response.