A large real-world test of Pfizer’s COVID-19 vaccine confirms that it’s very effective at preventing serious illness or death, even after one dose. The results come from a mass vaccination campaign in Israel. They give strong reassurance that the benefits seen in smaller tests persisted when the vaccine was used in a general population. The vaccine was 92% effective at preventing severe disease after two shots and 62% after one. Its estimated effectiveness for preventing death was 72% two to three weeks after the first shot. The New England Journal of Medicine published results Wednesday.