Differential effects of the second SARS-CoV-2 mRNA vaccine dose on T cell immunity in naive and COVID-19 recovered individuals

The rapid development of mRNA-based vaccines against the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) led to the design of accelerated vaccination schedules that have been extremely effective in naive individuals. While a two-dose immunization regimen with the BNT162b2 vaccine has been demonstrated to provide a 95% efficacy in naive individuals, the effects of the second vaccine dose in individuals who have previously recovered from natural SARS-CoV-2 infection has not been investigated in detail. In this study, we characterize SARS-CoV-2 spike-specific humoral and cellular immunity in naive and previously infected individuals during and after two doses of BNT162b2 vaccination. Our results demonstrate that, while the second dose increases both the humoral and cellular immunity in naive individuals, COVID-19 recovered individuals reach their peak of immunity after the first dose. These results suggests that a second dose, according to the current standard regimen of vaccination, may be not necessary in individuals previously infected with SARS-CoV-2. [Display omitted] •SARS-CoV-2 antigen-specific CD4+CD154+ Th1 cells secrete IL-2 and IFN-γ•T cell-mediated IL-2 and IFNγ correlate with SARS-CoV-2 IgG humoral immunity•Naive subjects reach their peak of immunity after the second vaccine dose•COVID-19 recovered individuals reach their peak of immunity after the first vaccine dose Scarce SARS-CoV-2 vaccine supplies are influencing vaccination policies in some countries. Lozano-Ojalvo et al. report that subjects with previous exposure to SARS-CoV-2 mount powerful immune responses after the first BNT162b2 vaccine dose, suggesting single vaccination regimens in COVID-19 recovered individuals.