Scientists urged people eligible to be vaccinated against Covid after major investigation in England refound evidence of "breakthrough infections " more than three months after full vaccination.
Researchers at Imperial College London analyzed more of 100,000 swabs from a random sample of the population and found that Covid infection rates were three to four times higher in unvaccinated people than in those who received two injections.
But while full vaccination has drastically lowered infection rates, by 1 , 76% in the unvaccinated to 0.35% in the three months after the second dose, infection rates increased again to 0.55% three to six months after the second injection.
The result suggests that protection against infection, with or without symptoms, begins to decline several months after full vaccination, although other studies show thatvaccine protection against hospitalization and death is much more robust.
"The possible increase in chronic infections over time reinforces the need for A booster program, "said Paul Elliott, head of the React study and professor of epidemiology and public health medicine at Imperial. "This is an incentive for people to receive their booster when it becomes available," added Professor Christl Donnelly, the study's statistical epidemiologist. The results came as new cases of Covid in the UK rose to 42,776, the highest recorded since late July.
The React study used community testing to provide regular snapshots of the outbreak in England throughout the Covid crisis. The latest data includes the results of 100,527 swabs taken between 9 and 27 September, and 9Another 8,233 swabs taken in June and July.
All of the viruses sequenced in the study were the highly transmissible Delta variant, with one sample carrying a mutation called E484K which can help the virus escape immunity from a past infection or vaccination. Delta's parent is monitored by the UK Health Security Agency.
Preliminary results of the survey, which has not yet been peer-reviewed, shows that the highest infection rates in September were among 5 to 17 year olds, with around 2.5% positive tests , followed by 35 to 54, the age group most likely to have children in school. Efforts to immunize healthy children 12 to 15 years of age and provide boosters for those aged50 years and over are now underway.
According to the study, full vaccination reduced the risk of infection, with or without symptoms, of 'about 60%. The Pfizer vaccine appeared to be more effective than that of AstraZeneca, but the vaccines were given to different age groups at different times of the epidemic, so they cannot be directly compared.
While previous studies have shown that antibodies to Covid decrease in the months following vaccination, recent work suggests that two doses are highly protective against serious illness. Last week, United States researchers reported that two injections of Pfizer vaccine provided 90% protection against hospitalization for at least six months, although protection against infection was halved in the course ofs from the same period.
The React survey shows that while infection rates for England were broadly stable in September, the overall picture masked distinct trends in particular age groups and regions. Infections were on the rise among ren schoolchildren, with the R number at 1.18 in those under 17 years of age. Rates were generally down among those aged 18 to 54 and stable among those aged 55 and over.
Although R, the number of people a person infected typically transmits the virus to, stood at 1.03 for England as a whole in September, infections appeared to be increasing in the East Midlands and London, with R at 1.36 and 1.59, according to the 'investigation. The infection rate was almost twice as high in black participants as in whites (1.41% vs. 0.78%), and more common in people living in mmore numerous and among people who shared their home with at least one child.