People who have received both doses of a Covid-19 vaccine are half as likely to be infected with the coronavirus than those who have not been vaccinated, according to a new study led by researchers at Imperial College London, though the scientists warned a new vaccine targeting the infectious delta variant may be needed to combat concerns over vaccine efficacy.
Fully vaccinated people are half as likely to catch Covid-19 than those who are unvaccinated, a … [+]
Three times as many unvaccinated people tested positive for Covid-19 than those who had not been vaccinated, the REACT study found, with all positive samples analyzed indicating an infection with the delta Covid-19 variant.
Once other factors are taken into account, the study, which is based on data from over 98,000 swab tests taken between June 24 and July 12 and has not yet been peer reviewed, indicates full vaccination halves the risk of catching Covid-19.
Fully vaccinated people who were infected with the virus tended to have less severe illness than unvaccinated people and seemed to have smaller amounts of virus in samples, the researchers added, meaning they may be less likely to pass it on if they are infected.
Professor Paul Elliott, director of the research program running the study, said the findings confirm “previous data showing that both doses of a vaccine offer good protection against getting infected,” but show there “is still a risk of infection among the fully vaccinated.”
The researchers estimated that two doses of a Covid-19 vaccine are 49% effective at preventing infection with the delta variant, in line with recent data from Israel and much lower than previous estimates.
“Development of vaccines against delta may be warranted” given the reduced effectiveness of current vaccines against the strain, the researchers wrote, warning that even high levels of vaccination may be unable to stop it spreading in the fall.
One in 26. That’s the chance of being infected with Covid-19 if you’re in contact with an infected individual and fully vaccinated, the researchers found. This is compared to a one in 13 chance for the unvaccinated.
Unvaccinated young people and the infectious delta variant are driving the new wave of cases in the U.K., the researchers said, a trend that is mirrored in the U.S. High vaccination rates in the country have helped contribute towards a possible decoupling between infection, severe illness and death, which prompted the government to drop almost all social restrictions on July 19 amid some of the highest infection rates in the world. However, experts still warn of the risks of long Covid should the virus be allowed to spread unchecked. The sometimes debilitating long-term after effects of an infection do not appear to be linked to how severe the initial infection was, though recent evidence indicates they may be less likely in children.
What We Don’t Know
The findings from this study suggest lower viral loads in the fully vaccinated people who are infected, which correspond with lower chances of passing the virus on to others. The CDC recently found signs vaccinated people may be just as infectious as the unvaccinated, however, and further research will be needed to settle the matter. A lower chance does not mean zero chance, and the CDC recommends even the fully vaccinated to wear masks in certain places.
Despite tangible evidence that unvaccinated people are driving new waves of Covid-19 in highly vaccinated countries—which has a far reaching impact beyond individual health—most unvaccinated Americans feel little responsibility for its spread, a recent poll indicates. Opposition to vaccination has hardly shifted in months and some employers have started to require vaccines for their employees to boost flagging numbers.