Humoral and cell-mediated response elicited by SARS-CoV-2 mRNA vaccine BNT162b2 e in healthcare workers: a longitudinal observational study

Cassaniti, Irene; Bergami, Federica; Percivalle, Elena; Gabanti, Elisa; Sammartino, Josè Camilla; Ferrari, Alessandro; Guy Adzasehoun, Kodjo Messan; Zavaglio, Federica; Zelini, Paola; Comolli, Giuditta; Sarasini, Antonella; Piralla, Antonio; Ricciardi, Alessandra; Zuccaro, Valentina; Maggi, Fabrizio; Novazzi, Federica; Simonelli, Luca; Varani, Luca; Lilleri, Daniele; Baldanti, Fausto

OBJECTIVES: To assess SARS-CoV-2 humoral and cell-mediated response elicited by mRNA BNT162b2 vaccine in SARS-CoV-2 experienced and naïve subjects against reference strain and SARS-CoV-2 variants. METHODS: Humoral response, including neutralizing antibodies, and T-cell mediated response elicited by BNT162b2 vaccine in 145 healthcare workers (both naïve and positive for previous SARS-CoV-2 infection) were evaluated. In a subset of subjects, effect of SARS-CoV-2 variants on antibody level and cell-mediated response was also investigated. RESULTS: Overall 125/127 (98.4%) naïve subjects developed both neutralizing antibodies and specific T-cells after the second dose. Moreover, the antibody and T-cell responses were effective against viral variants since SARS-CoV-2 NT Abs were still detectable in 55/68 (80.9%) and 25/29 (86.2%) naïve subjects when sera were challenged against beta and delta variants, respectively.T-cell response was less affected, with no significant difference in the frequency of responders (p=0.369). Of note, two-dose of vaccine was able to elicited sustained neutralizing antibody activity against all the SARS-CoV-2 tested variants in SARS-CoV-2 experienced subjects. CONCLUSIONS: BNT162b2 vaccine elicited a sustained humoral and cell-mediated response in immunocompetent subjects after two-dose administration and it seems to be less affected by SARS-CoV-2 variants, with the only exception of beta and delta variants. An increased immunogenicity, also against SARS-CoV-2 variant strains was observed in SARS-CoV-2 experienced subjects. These results suggest that triple exposure to SARS-CoV-2 antigens might be proposed as valuable strategy for vaccination campaign.