A phase I/II trial evaluated the immune responses induced by the BNT162b1 mRNA vaccine, which encodes the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein. The vaccine was administered in doses of 1–50 µg to healthy adults aged 18–55 years, with two doses eliciting robust CD4+ and CD8+ T cell responses and strong antibody responses. RBD-binding IgG concentrations were significantly higher than those in convalescent sera from individuals who had recovered from COVID-19. Neutralizing antibody titres were also elevated, with geometric mean titres reaching 1.9–4.6-fold those of convalescent sera. The vaccine induced T helper type 1 (TH1)-skewed T cell responses, with IFN-γ production by a large fraction of RBD-specific CD8+ and CD4+ T cells. The BNT162b1 vaccine showed strong immune responses, including high levels of RBD-specific antibodies and T cells, suggesting its potential to protect against COVID-19 through multiple mechanisms. The vaccine was well-tolerated, with mostly mild to moderate local and systemic reactions. The study confirmed the dose-dependent increase in RBD-binding IgG and neutralizing antibody responses, and the vaccine induced a strong boost response. The results support the use of BNT162b1 as a candidate vaccine for COVID-19. The study also demonstrated the breadth of the neutralizing response against various SARS-CoV-2 spike variants. The vaccine induced functional and proinflammatory CD4+ and CD8+ T cell responses, with TH1 polarization of the helper response. The study highlights the potential of the BNT162b1 vaccine to induce a strong immune response against SARS-CoV-2. The results are consistent with previous findings from the USA trial. The vaccine was well-tolerated, with mostly mild to moderate local and systemic reactions. The study also demonstrated the breadth of the neutralizing response against various SARS-CoV-2 spike variants. The vaccine induced functional and proinflammatory CD4+ and CD8+ T cell responses, with TH1 polarization of the helper response. The study highlights the potential of the BNT162b1 vaccine to induce a strong immune response against SARS-CoV-2. The results are consistent with previous findings from the USA trial.A phase I/II trial evaluated the immune responses induced by the BNT162b1 mRNA vaccine, which encodes the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein. The vaccine was administered in doses of 1–50 µg to healthy adults aged 18–55 years, with two doses eliciting robust CD4+ and CD8+ T cell responses and strong antibody responses. RBD-binding IgG concentrations were significantly higher than those in convalescent sera from individuals who had recovered from COVID-19. Neutralizing antibody titres were also elevated, with geometric mean titres reaching 1.9–4.6-fold those of convalescent sera. The vaccine induced T helper type 1 (TH1)-skewed T cell responses, with IFN-γ production by a large fraction of RBD-specific CD8+ and CD4+ T cells. The BNT162b1 vaccine showed strong immune responses, including high levels of RBD-specific antibodies and T cells, suggesting its potential to protect against COVID-19 through multiple mechanisms. The vaccine was well-tolerated, with mostly mild to moderate local and systemic reactions. The study confirmed the dose-dependent increase in RBD-binding IgG and neutralizing antibody responses, and the vaccine induced a strong boost response. The results support the use of BNT162b1 as a candidate vaccine for COVID-19. The study also demonstrated the breadth of the neutralizing response against various SARS-CoV-2 spike variants. The vaccine induced functional and proinflammatory CD4+ and CD8+ T cell responses, with TH1 polarization of the helper response. The study highlights the potential of the BNT162b1 vaccine to induce a strong immune response against SARS-CoV-2. The results are consistent with previous findings from the USA trial. The vaccine was well-tolerated, with mostly mild to moderate local and systemic reactions. The study also demonstrated the breadth of the neutralizing response against various SARS-CoV-2 spike variants. The vaccine induced functional and proinflammatory CD4+ and CD8+ T cell responses, with TH1 polarization of the helper response. The study highlights the potential of the BNT162b1 vaccine to induce a strong immune response against SARS-CoV-2. The results are consistent with previous findings from the USA trial.