Link between S- and N-Protein IgG levels after the first BNT162b2 dose
Among the RT-PCR-positive residents, the median levels of S-protein IgG after vaccine were ranked in the following order: i ) residents with a newer infection and no detectable N-protein IgG (median value of 230AU/mL), ii ) residents with a newer infection and detectable N-protein IgG (median value of 20,685 AU/mL), iii ) residents with an older infection and no detectable N-protein IgG (median value of 27,313 AU/mL), and iv ) residents with an older infection and detectable N-protein IgG (median value of 40,000 AU/mL)(Table 2, Figure 2).
The predictive value of a high S-protein IgG level (≥ 4,160 UA/ ml) by N-protein IgG (≥ 0.8 signal to cutoff ratio) was high (positive predictive value of 92.5% [90.8%-94.2%] and negative predictive value of 93.0% [91.4%-94.6%]).
S-protein IgG levels 6 weeks after the second BNT162b2 jab
Six weeks after the second BNT162b2 jab, only around 3% of the 554 residents without prior COVID-19 had undetectable S-protein IgG levels (< 50 AU/mL) vs none of the residents with a prior positive PCR (Table 3). The prevalence of residents with low S-protein IgG levels (≤ 1,050 AU/mL) was significantly lower in residents without prior COVID-19 than in those with a positive PCR in the 3 to 12 last months (28.3% vs 2.7%, p<0.001) (Figure 3). The median value of S-protein IgG in residents without prior COVID-19 after two vaccine doses was 10-fold lower than that in residents with prior COVID-19 after one dose (2,384 AU/mL vs 23,259 AU/mL)