Monitoring of the immunogenic response to Pfizer BNT162b2 mRNA COVID-19 vaccination in healthcare workers with Snibe SARS-CoV-2 S-RBD IgG chemiluminescent immunoassay

The final study population consisted of 194 consecutive healthcare workers, who received the complete vaccine cycle (median age 42 years, 59.3% females), 30 (15.5%) of whom were SARS-CoV-2 positive at baseline. Pfizer BNT162b2 mRNA vaccination was effective to elicit an increase of IgG anti-S-RBD levels in both cohorts of baseline SARS-CoV-2 seronegative and seropositive subjects. More specifically, in baseline SARS-CoV-2 seronegative subjects the median IgG anti-S-RBD levels were 0.35 kU/L before vaccination, increasing to 44.15 kU/L at T1 (21 days after the first dose) and 513.15 kU/L at T2 (30 days after the second dose), respectively. The corresponding median levels in baseline seropositive subjects were 1.70 kU/L before vaccination, increasing to 74.65 kU/L at T1 and 718.35 kU/L at T2, respectively. The median IgG anti-S-RBD levels elicited by COVID-19 vaccination was significantly higher in baseline SARS-CoV-2 seropositive than seronegative subjects at T0, T1 and also T2. Seropositivization occurred in all except one baseline SARS-CoV-2 seronegative subjects at T1 (163/164; 99.4%), and in all subjects at T2 (164/164; 100%). The full Snibe IgG anti-S-RBD antibodies response at T2 (expressed as T2/T0 ratio) did not significantly correlate with age (r=-0.14; p=0.076) or sex (r=-0.06; p=0.436). The Spearman’s correlation between Snibe IgG anti-S-RBD and Roche total anti-SARS-CoV-2 S serum levels at T1 and T2 showed coefficients between 0.70 and 0.96.