Covid-19 vaccines developed by Pfizer Inc with BioNTech SE and Moderna Inc reduced risk of infection by 80% two weeks or more after the first of two shots, according to data from a real-world US study released on Monday.<br /><br />The risk of infection fell 90% by two weeks after the second shot, the study of nearly 4,000 US healthcare personnel and first responders found.<br /><br />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.
