Pfizer, Moderna COVID-19 vaccines highly effective after first shot in real-world use, -U.S. study

COVID-19 vaccines developed by Pfizer Inc with BioNTech SE and Moderna Inc reduced the risk of infection by 80% 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% by two weeks after the second shot, the study of just under 4,000 vaccinated U.S. healthcare personnel and first responders found. The study by the U.S. Centers for Disease Control and Prevention (CDC) evaluated the vaccines' ability to protect against infection, including infections that did not cause symptoms. Previous clinical trials by the companies evaluated their vaccine's efficacy in preventing illness from COVID-19.