ABSTRACT
Background: Little is known about the induction of mucosal Ab after the 3rd dose. We reported that two doses of BNT162b2 induced mucosal Abs as early as 14-days after the 1st dose. As BNT162b2 only provides the RNA encoding a full-length spike (S) protein, a mixed-vaccine regime with a vaccine that provides inactivated but intact viral particles was executed in some countries to expand the diversity of SARS-CoV-2 Abs. Aim and objectives: To examine the mucosal and plasma Ab induction in vaccine recipients receiving their 3rd vaccine dose with single or mixed vaccine type. Method(s): 46 healthy subjects who had BNT162b2 (B) or CoronaVac (C) in a sequence of either BBB, BBC, CCC or CCB were recruited for a longitudinal sampling of nasal fluid and blood. The S1-specific Ab and neutralizing Ab against SARS-CoV-2 VOCs were measured. Result(s): All BBB recipients (n=28) had nasal specific S1-IgA and IgG after two doses, and the Abs lasted six months and were readily induced after the 3rd dose. In BBC recipients (n=4), though they had prior induction of nasal Abs after two doses of B, the inactivated vaccine did not boost their nasal Abs. In CCC recipients (n=5), there was no induction on nasal Abs. If they adopted the CCB regime (CCB, n=11), they acquired nasal Ab after the 3rd dose. The nasal neutralizing antibodies against the wild type were boosted in 20/28 of the BBB recipients and induced in 8/11 of the CCB recipients but not in CCC or BBC recipients. Lastly, all 46 subjects had a boosted specific S1-IgA and S1IgG in plasma. Conclusion(s): Our findings highlighted the uniqueness of BNT162b2 in induing nasal Ab regardless of the vaccination history.