Pfizer, Moderna vaccines: Infection risk down by 80% after first shot

WASHINGTON: 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 US 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 US 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.

Some countries dealing with limited vaccine supplies have pushed back schedules for second doses with the hope of getting some protection to more people.

US public health officials, however, continue to recommend two doses be given on the schedule authorised by regulators based on clinical trials.

The study by the US Centres 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, but those studies would have missed asymptomatic infections.

The study looked at the effectiveness of the mRNA vaccines among 3,950 participants in six states over a 13-week period from Dec 14, 2020, to March 13 this year.

"The authorised mRNA Covid-19 vaccines provided early, substantial real-world protection against infection for our nation's healthcare personnel, first responders, and other front-line essential workers," CDC Director Rochelle Walensky said in a statement. - REUTERS