A large observational, real-world study from Israel estimates that the Pfizer/BioNTech COVID-19 vaccine is 46% effective at preventing infection 14 to 20 days after the first dose and 92% 7 days after the second dose, backing the results of an earlier randomized, controlled trial, according to a study today in the New England Journal of Medicine (NEJM).A single dose, however, was 74% effective against COVID-related hospitalization and 72% effective at preventing death.Led by scientists from the Clalit Research Institute in Tel Aviv, the study involved comparing patients who received the BNT162b2 vaccine from Dec 20, 2020, to Feb 1, 2021, to 1-to-1 matched controls.