COVID-19 vaccines developed by Pfizer-BioNTech and Moderna reduced risk of infection by 80 per cent two weeks or more after the first of two shots, according to data from a real-world U.S.
study released on Monday.The risk of infection fell 90 per cent by two weeks after the second shot, the study of nearly 4,000 U.S.
healthcare personnel and first responders found.The results validate earlier studies that had indicated the vaccines begin to work soon after a first dose, and confirm that they also prevent asymptomatic infections.
Early data shows single COVID-19 shot remarkably effective, researchers say Some countries dealing with limited vaccine supplies have pushed back schedules for second doses with the hope of getting some.