key: cord-0701038-rivyxfoo
authors: 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
title: Humoral and cell-mediated response elicited by SARS-CoV-2 mRNA vaccine BNT162b2 e in healthcare workers: a longitudinal observational study
date: 2021-09-25
journal: Clin Microbiol Infect
DOI: 10.1016/j.cmi.2021.09.016
sha: 59d829196d441cb3eef077d0338f0b177ca7842f
doc_id: 701038
cord_uid: rivyxfoo

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.

The mRNA BNT162b2 vaccine [1] , the first authorized for SARS-CoV-2 infection, showed a 48 95% protection against SARS-CoV-2 infection in a phase 2/3 trial [2] . Another mRNA-based vaccine, 49 mRNA-1273 [3] showed similar effect. However, data on the kinetics of immune response elicited 50 by the vaccines are limited to low numbers of subjects analyzed and mainly to the antibody response 51 [1, [4] [5] [6] [7] [8] . 52 The T-cell response elicited by the vaccine may have a crucial role in the long-term protection 53 from SARS-CoV-2 infection and disease. In convalescent subjects, T-and B-cell memory specific 54 for SARS-CoV-2 was found to persist for at least 6-8 months [9] [10] [11] . 55 The emergence of new SARS-CoV-2 variants with mutations in the Spike protein has raising 56 significant concerns about vaccines efficacy or reinfection risk in previously infected subjects. The Analyses were performed at baseline (before vaccination), at time of second vaccine administration 80 (T1) and 21 days after the second dose (T2).

Antibody response was determined using the chemiluminescent assay Elecsys Anti-SARS-CoV-2 S 82 (Roche Diagnostics Rotkreuz, Switzerland), which provides quantitative measures of antibody 83 (mainly IgG) specific for SARS-CoV-2 RBD. Results are given as units (U)/ml and are considered 84 positive when ≥0.8 U/ml. Moreover, SARS-CoV-2 neutralizing antibodies were quantified using a 85 home-made assay and results higher than 1:10 were considered positive. IgG against RBD of the 86 wild-type (WT) and European (EU, which share the same RBD), alpha and beta strains were 87 determined by ELISA using recombinant proteins. subjects developed anti-RBD antibodies, although at significantly lower levels than experienced subjects did. Moreover, levels of anti-RBD antibodies in naïve subjects at T1 were significantly lower 98 (p=0.009) than baseline levels of experienced subjects.

At T2, all the SARS-CoV-2-naïve subjects developed a positive anti-RBD response; however, 100 the median anti-RBD level was still significantly higher in SARS-CoV-2-experienced than naïve 101 subjects (p<0.001). (Fig. 1a) 

A similar trend was observed for NT antibodies (Figure 1b) . Serum NT titres were 103 significantly higher in SARS-CoV-2-experienced than naïve subjects at any time point. 

Similarly to what observed for the beta variant, a six-fold decrease of NT level was documented 152 against the B.1.525 strain (p=0.081; Fig S4) . Of note, no correlation was observed between RBD 153 level and NT antibody titre for each variant (Fig S5) .

In 36 vaccinated subjects (53%), residual PBMC isolated at T2 were challenged against 155 inactivated virus preparations from supernatant of Vero E6 cells infected with five SARS-CoV-2 156 strains (WT, EU, alpha, beta and gamma) and cell-mediated response was analysed by ELISpot assay.

The ELISpot assay was less sensitive using WT virus than peptide pools from the homologous S 

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