Effect of recent SARS-CoV-2 infection on anti-spike protein immunoglobulin G II response after BNT162b2 vaccination

Our hospital experienced a SARS-CoV-2 outbreak 3 months before staff vaccination was initiated. This study compared antibody responses to the first and second doses of BNT162b2 mRNA vaccine among staff with and without prior infection. Serum anti-spike (S) protein immunoglobulin (anti-S) IgG, IgM, and anti-nuclear (N) protein IgG, IgM were measured 1 week before the first dose (baseline). Serum anti-S IgG II levels were sequentially measured at the baseline, 3 weeks after the first dose (immediately prior to the second dose), and 3 weeks and 6 months after the second dose to assess neutralization activity. Ten of the 83 staff had evidence of prior SARS-CoV-2 infection. The baseline anti-S IgG, IgG II, anti-N IgM, and anti-N IgG levels were significantly higher in those with prior infection. Three weeks after the first dose, the mean anti-S IgG II level was significantly higher in the prior-infection group (406.94 ± 163.44 AU/mL) than that in the uninfected group (40.43 ± 50.16 AU/mL; p < 0.001). Three weeks after the second dose, the mean anti-S IgG II level was significantly lower than that after the first dose in the prior-infection group (240.28 ± 81.46 AU/mL; p = 0.007), and significantly higher in the uninfected group (341.45 ± 192.75 AU/mL; p < 0.001). Six months after the second dose, the mean anti-S IgG II levels did not differ significantly between groups. A single dose of BNT162b2 vaccine is sufficient to induce a peak anti-S IgG II response in recently infected individuals.