Comprehensive assessment of humoral response after Pfizer BNT162b2 mRNA Covid-19 vaccination: a three-case series

Abstract

Background. Since universal vaccination is a pillar against coronavirus disease 2019 (COVID-19), monitoring anti-SARS-CoV-2 neutralizing antibodies is essential for deciphering post-vaccination immune response. Methods. Three healthcare workers received 30 g BNT162b2 mRNA Covid-19 Vaccine, followed by a second identical dose, 21 days afterwards. Venous blood was drawn at baseline and at serial intervals, up to 63 days afterwards, for assessing total immunoglobulins (Ig) anti-RBD (receptor binding domain), IgG anti-S1/S2, IgG anti-RBD, IgM anti-RBD, IgM anti-N/S1 and IgA anti-S1. Results. All subjects were SARS-CoV-2 seronegative at baseline. Total Ig anti-RBD, IgG anti-S1/S2 and IgG anti-RBD levels increased between 91-368 folds until 21 days after the first vaccine dose, then reached a plateau. The levels raised further after the second dose (by ~30-, ~8- and ~8-fold, respectively), peaking at day 35, but then slightly declining and stabilizing ~50 days after the first dose. IgA anti-S1 levels increased between 7-11 days after the first dose, slightly declined before the second dose, after which levels augmented by ~24-fold from baseline. The anti-RBD and anti-N/S1 IgM kinetics were similar to that of anti-S1 IgA, though displaying substantially weaker increases and modest peaks, only 4 to 7-fold higher than baseline. Highly significant inter-correlation was noted between total Ig anti-RBD, anti-S1/S2 and anti-RBD IgG (all r=0.99), whilst other anti-SARS-CoV-2 antibodies displayed lower, though still significant, correlations. Serum spike protein concentration was undetectable at all time points. Conclusions. BNT162b2 mRNA vaccination generates a robust humoral immune response, especially involving IgG and IgA, magnified by the second vaccine dose.