Evaluation of the effectiveness of BNT162b2 primary vaccination and booster dose to SARS-CoV-2 in eliciting stable mucosal immunity

The waning effectiveness of the primary vaccination for SARS-CoV-2 led to administration of an additional booster dose (BD). The efficacy of the BD in stimulating humoral systemic immune response is well established, but its effectiveness on inducing mucosal immune reaction has not yet been reported. To address this issue, we evaluated SARS-CoV-2-specific antibody responses in the serum, saliva, and tears after BNT162b2 (Pfizer/BioNTech, New York, NY, USA) vaccination and BD, as well as after SARS-CoV-2 infection. After two doses of BNT162b2 vaccine, we observed specific serum IgG in 100% and IgA in 97.2% of subjects, associated with mucosal response in both salivary samples (sIgA in 97.2% and IgG(S) in 58.8%) and in tears (sIgA in 77.8% and IgG(S) in 67.7%). BD induced a recovery of the systemic humoral response and of tear sIgA when compared to 6 months of follow-up titers (p < 0.001; p = 0.012). However, sIgA levels in both tears and saliva were significantly lower following BD when compared to patients with prior SARS-CoV-2 infection (p = 0.001 and p = 0.005, respectively). Our results demonstrated that administration of BD restored high serum levels of both IgG and IgA but had a poor effect in stimulating mucosal immunity when compared to prior SARS-CoV-2 infection.