Vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is effective in preventing hospitalization from severe COVID-19. However, multiple reports of breakthrough infections and of waning antibody titers have raised concerns on the durability of the vaccine, and current vaccination strategies now propose administration of a third dose. Here, we monitored T cell responses to the Spike protein of SARS-CoV-2 in 71 healthy donors vaccinated with two doses of the Pfizer-BioNTech mRNA vaccine (BNT162b2) for up to 6 months after vaccination. We found that vaccination induced the development of a sustained anti-viral CD4⁺ and CD8⁺ T cell response. These cells appeared before the development of high antibody titers, displayed markers of immunological maturity and stem cell memory, survived the physiological contraction of the immune response, and persisted for at least 6 months. Collectively, these data show that vaccination with BNT162b2 elicits an immunologically competent and long-lived SARS-CoV-2–specific T cell population.