Anti-SARS-CoV-2 IgG antibodies in patients with or without SARS-CoV-2 infection after BNT162b2 vaccine booster

The final study population consisted of 67 baseline seronegative (i.e. pre-vaccination) healthcare workers, 14 with (median age, 42 years; IQR, 31-48 years; 29% of females) or 53 without (median age, 46 years; IQR, 34-54 years, 60% of females) a diagnosis of SARS-CoV-2 infection within 4 weeks after receiving the homologous booster vaccine dose. No significant difference in serum concentration of anti-SARS-CoV-2 spike trimeric IgG levels was observed throughout the study period (all p>0.05) between subjects with or without diagnosis of post-booster SARS-CoV-2 infection. Although the median levels of anti-SARS-CoV-2 spike trimeric IgG at 1 month after receiving the booster vaccine dose appeared slightly higher in subjects with post-booster SARS-CoV-2 infection (11,720 kBAU/L; IQR, 4,543-16,775 kBAU/L) than in those without (8,700 kBAU/L; IQR, 5,463-15,733 kBAU/L), this difference was not statistically significant (p=0.257). The rate of subjects with protective values (i.e., >264 kBAU/L, corresponding to the 80% limit of COVID-19 vaccine efficacy against symptomatic disease) was 100% in both cohorts after booster vaccine dose.