People who receive Covid-19 vaccines by Pfizer and Moderna are up to 91 per cent less likely to develop the disease, according to a US study, which also suggests that the preventives reduce the severity of symptoms and duration in those who still get an infection.
The research, published in the New England Journal of Medicine on June 30, is among the first to show the benefits of mRNA vaccines even among those who experience breakthrough infections -- testing positive after immunisation.
"One of the unique things about this study is that it measured the secondary benefits of the vaccines," said study co-author Sarang Yoon, an assistant professor at the University of Utah, US.
The study was designed to measure the risks and rates of infection among those on the front lines of the pandemic -- doctors, nurses, and first responders.
The study found that mRNA Covid-19 vaccines were 91 per cent effective in reducing risk for infection once participants were 'fully' vaccinated, two weeks after the second dose.
The researchers also found that the vaccines are 81 per cent effective in reducing risk for infection after "partial" immunisation, two weeks after the first dose was given.
The study recruited 3,975 participants at eight sites in the US. Participants submitted samples for Covid-19 testing on a weekly basis for 17 weeks between December 13, 2020 and April 10, 2021.
Only 204 (5 per cent) of the participants eventually tested positive for SARS-CoV-2, the virus that causes Covid-19. Of these, 156 were unvaccinated, 32 had an indeterminate vaccine status, and 16 were fully or partially vaccinated. The fully or partially vaccinated participants who developed breakthrough had milder symptoms than those who were unvaccinated.