T-cell response after first dose of BNT162b2 SARS-CoV-2 vaccine among healthcare workers with previous infection or cross-reactive immunity.

Objectives: Antibody response to the first dose of BNT162b2 SARS-CoV-2 is greater in COVID-19-convalescent than in infection-naïve individuals. However, there are no data about T-cell response in individuals with pre-existing cellular immunity.

Methods: We evaluated T-cell responses in parallel with SARS-CoV-2 antibody level after first dose of BNT162b2 vaccine in 23 infection-naïve and 27 convalescent healthcare workers (HCWs) previously included in a study about humoral and T-cell immunity.

Results: Overall, the antibody response was lower in the infection-naïve group than in convalescent individuals (18 895 vs 662.7 AU mL,  < 0.001), and intermediate but significantly lower in convalescent HCWs with previous negative serology (25 174 vs 1793 AU mL;  = 0.015). Indeed, anti-spike IgG titres after the first dose correlated with baseline anti-nucleocapsid IgG titres (rho = 0.689;  < 0.001). Pre-existing T-cell immunity was observed in 78% of convalescent and 65% of the infection-naïve HCWs. T-cell response after the first dose of the vaccine was observed in nearly all the cases with pre-existing T-cell immunity, reaching 94% in convalescent HCWs and 93% in those with cross-reactive T cells. It was lower in the infection-naïve group (50%;  = 0.087) and in convalescent HCWs with negative serology (56%;  = 0.085). Notably, systemic reactogenicity after vaccination was mainly observed in those with pre-existing T-cell immunity ( = 0.051).

Conclusion: Here, we report that the first dose of BTN162b2 elicits a similar S-specific T-cell response in cases of either past infection or cross-reactive T cells, but lower in the rest of infection-naïve individuals and in convalescent HCWs who have lost detectable specific antibodies during follow-up.