Up until now, most data on the efficacy of COVID-19 vaccines has come under controlled conditions in clinical trials, leaving an element of uncertainty over how results would translate into the real world with its unpredictable variables. The research in Israel - two months into one of the world’s fastest rollouts, providing a rich source of data - showed two doses of the Pfizer shot cut symptomatic COVID-19 cases by 94% across all age groups, and severe illnesses by nearly as much. The study of about 1.2 million people also showed a single shot was 57% effective in protecting against symptomatic infections after two weeks, according to the data published and peer-reviewed in the New England Journal of Medicine on Wednesday.