Scientists have urged eligible people to have Covid vaccine booster shots after a major survey in England found evidence of greater levels of breakthrough infections more than three months after full vaccination.
Researchers at Imperial College London analysed more than 100,000 swabs from a random sample of the population and found that Covid infection rates were three to four times higher among unvaccinated people than among those who had received two shots of a Covid-19 vaccine.
But while full vaccination drove infection rates down substantially, from 1.76 per cent in the unvaccinated to 0.35 per cent in the three months after the second dose, infection rates rose again to 0.55 per cent three to six months after the second shot.
The finding suggests that protection against infection, with or without symptoms, starts to wane several months after full vaccination, although other studies show that vaccine protection against hospitalisation and death from Covid-19 is far more robust.
"The possible increase of breakthrough infections over time reinforces the need for a booster programme," says Prof Paul Elliott, head of the React study and professor of epidemiology and public-health medicine at Imperial.
"It's an incentive for people to get their booster dose when it becomes available to them," adds Prof Christl Donnelly, a statistical epidemiologist on the study.
All of the viruses sequenced in the study were the highly transmissible Delta variant, with one sample carrying a mutation, called E484K, that may help the virus evade immunity from past infection or vaccination.
Preliminary results from the survey, which are not yet peer-reviewed, show that the highest rates of infection in September were among five- to 17-year-olds, with about 2.5 per cent of this cohort testing positive, followed by 35- to 54-year-olds, the age group most likely to have children at school.
According to the study, full vaccination reduced the risk of infection, with or without symptoms, by about 60 per cent.
While previous studies have shown that antibodies against Covid decline in the months after vaccination, recent work suggests that two doses are highly protective against severe disease. Last week, US researchers reported that two shots of the Pfizer vaccine were 90 per cent protective against hospitalisation for at least six months, even though protection against infection halved over the same period.– Guardian
