Covid-19 vaccines developed by Pfizer with BioNTech and Moderna reduced the risk of infection by 80 per cent two weeks or more after the first of two shots, according to data from a real-world study of vaccinated US healthcare personnel and first responders released on Monday (March 29).
The risk of infection fell 90 per cent by two weeks after the second shot, the study of just under 4,000 people found.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.
The findings from of the real-world use of these messenger RNA (mRNA) vaccines confirm what was seen in large controlled clinical trials conducted before they received emergency use authorisations from the US Food and Drug Administration. Earlier clinical trials had established that the shots also prevent illness, hospitalisations and deaths.
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, 2021.
These groups were among the first to be vaccinated, along with the vulnerable elderly, because of their risk of exposure to the virus. Participants were tested for Covid-19 weekly and surveyed for reports of symptoms. The researchers compared the frequency of Covid infections before and after vaccinations to estimate how effective the shots were at preventing Sars-CoV-2 spread, regardless of whether people felt sick or not.
The new mRNA technology is a synthetic form of a natural chemical messenger being used to instruct cells to make proteins that mirror part of the novel coronavirus. That teaches the immune system to recognise and attack the actual virus.
(The Straits Times)