The study evaluates the safety and efficacy of the BNT162b2 mRNA Covid-19 vaccine through 6 months after vaccination. The vaccine, which is highly efficacious against Covid-19, was found to be safe and have an acceptable adverse-event profile. Vaccine efficacy against Covid-19 was 91.3% (95% CI, 89.0 to 93.2) among participants without evidence of previous SARS-CoV-2 infection, with a gradual decline in efficacy over time. Efficacy against severe disease was 96.7% (95% CI, 80.3 to 99.9). In South Africa, where the B.1.351 variant was prevalent, the vaccine efficacy was 100% (95% CI, 53.5 to 100). The vaccine showed consistent efficacy across diverse populations, including age, sex, race, and risk factors for Covid-19. Safety data confirmed the favorable safety profile observed at a median of 2 months after immunization. The study concludes that BNT162b2 remains highly effective in preventing Covid-19 up to 6 months after the second dose, despite the emergence of SARS-CoV-2 variants.The study evaluates the safety and efficacy of the BNT162b2 mRNA Covid-19 vaccine through 6 months after vaccination. The vaccine, which is highly efficacious against Covid-19, was found to be safe and have an acceptable adverse-event profile. Vaccine efficacy against Covid-19 was 91.3% (95% CI, 89.0 to 93.2) among participants without evidence of previous SARS-CoV-2 infection, with a gradual decline in efficacy over time. Efficacy against severe disease was 96.7% (95% CI, 80.3 to 99.9). In South Africa, where the B.1.351 variant was prevalent, the vaccine efficacy was 100% (95% CI, 53.5 to 100). The vaccine showed consistent efficacy across diverse populations, including age, sex, race, and risk factors for Covid-19. Safety data confirmed the favorable safety profile observed at a median of 2 months after immunization. The study concludes that BNT162b2 remains highly effective in preventing Covid-19 up to 6 months after the second dose, despite the emergence of SARS-CoV-2 variants.