The Pfizer vaccine is very effective. Pfizer’s initial Phase 3 clinical data showed its vaccine to have 95% effectiveness. In April 2021, Pfizer reported that the vaccine had 91.3% effectiveness against COVID-19, based on measuring how well it prevented symptomatic COVID-19 infection seven days through up to six months after the second dose. It also found it to be 100% effective in preventing severe disease as defined by the CDC, and 95.3% effective in preventing severe disease as defined by the FDA. Another study, not yet peer-reviewed, provided more new data that brought the efficacy number down to 84% after 6 months, although efficacy against severe disease was 97%.
SOURCE: https://www.yalemedicine.org/news/covid-19-vaccine-comparison (Yale Medicine)