How effective is the COVID-19 vaccine developed by Pfizer and BioNTech?

Results from the Pfizer/BioNTech vaccine trial were published in the New England Journal of Medicine. The data showed that the vaccine reduced the risk of COVID-19 by 95%. The trial enrolled nearly 44,000 adults, each of whom got two shots, spaced three weeks apart; half received the vaccine and half got a placebo (a shot of salt water). Of the 170 cases of COVID-19 that developed in the study participants, 162 were in the placebo group and eight were in the vaccine group. Nine of the 10 severe COVID cases occurred in the placebo group, suggesting that the vaccine reduced the risk of both mild and severe COVID.

According to the NEJM article, the vaccine was similarly effective in study participants of different races and ethnicities, bodyweight categories, presence or absence of coexisting medical conditions, and ages (younger and older than 65).