According to an ongoing population survey released Wednesday, fully vaccinated people in England had a third of the chance of testing positive for Covid-19.
The latest findings, from a long-term study by scientists at Imperial College London and market research firm Ipsos MORI, were based on 98,233 swabs taken between June 24 and July 12.
They showed one in 160 people infected with coronavirus, with a prevalence of 1.21 percent for unvaccinated respondents and 0.40 percent for those who were completely stung.
The study also found that double-vaccinated people may be less likely to pass the virus on to others than those who have not received a vaccine.
However, officials and scientists in Britain have urged caution after the government relaxed all virus restrictions in England on July 19, including the legal requirement to wear masks in certain indoor environments.
A US government document leaked last week warned that infections among fully vaccinated people are not as rare as previously thought and such cases are highly contagious.
Paul Elliott, a professor at Imperial’s School of Public Health and director of the research program, said the findings “confirm our previous data showing that both doses of a vaccine provide good protection against infection.”
“But we can also see that there is still a risk of infection as no vaccine is 100 percent effective, and we know that some doubly vaccinated people can still get sick from the virus.
“So even with the easing of restrictions, we still need to be careful to help protect each other and reduce the number of infections.”
Covid-19 cases recorded daily by the UK Department of Health have declined since the rules were relaxed, while population surveys have suggested they are still increasing, albeit at a slower pace.
The trend has taken experts and officials by surprise, who predicted a wave of new infections.
The Imperial-Ipsos study — covering the period up to July 12 — showed that even then, cases increased more gradually than during the previous month.