Scientists are urging eligible people to get their Covid booster injections after a large survey in England found evidence of “breakthrough infections” more than three months after a full vaccination.
Researchers at Imperial College London analyzed more than 100,000 swabs from a random sample of the population and found that rates of COVID-19 were three to four times higher among unvaccinated people than those who received two doses.
But while full vaccination reduced infection rates dramatically, from 1.76% in the unvaccinated to 0.35% in the three months after the second dose, infection rates rose again to 0.55% three to six months after the second injection.
The results suggest that protection against infection, with or without symptoms, begins to wane several months after full vaccination, although other studies show that the vaccine’s protection against hospitalization and death is much stronger.
“The potential increase in superinfections over time reinforces the need for an enhanced program,” said Paul Elliott, lead study leader for React and professor of epidemiology and public health medicine at Imperial. “It’s an incentive for people to get their booster doses when it becomes available to them,” Professor Christel Donnelly, a statistical epidemiologist on the study added. The results came as new Covid cases in the UK rose to 42,776, the highest level recorded since late July.
The React study used community testing to provide regular snapshots of the epidemic in England throughout the Covid crisis. The most recent data includes results from 100,527 swabs submitted between September 9 and 27, and another 98,233 swabs taken in June and July.
All viruses sequenced in the study were of a highly transmissible delta variant, with one sample carrying a mutation called E484K that may help the virus evade immunity from previous infection or vaccination. The Delta relative is monitored by the UK’s Health Security Agency.
Preliminary survey results, which have not yet been peer-reviewed, show that the highest infection rates in September were between 5 to 17 years old, with about 2.5% testing positive, followed by 35 to 54, the age group most likely to have children in school. . Efforts are now being made to vaccinate healthy people between the ages of 12 and 15 and provide boosters to those 50 and older.
According to the study, full vaccination reduced the risk of developing asymptomatic or asymptomatic by about 60%. The Pfizer vaccine appears to be more effective than the AstraZeneca vaccine, but the vaccines were given to different age groups at different points in the epidemic, so they cannot be compared directly.
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. US researchers reported last week that two shots of the Pfizer vaccine were 90% protective against at least six months of hospitalization, even though protection against infection was halved over the same period.
The React survey showed that while infection rates in England were broadly flat in September, the overall picture masked distinct trends in certain age groups and regions. Infections have been rising sharply in schoolchildren, with an R number of 1.18 in those under 17. Rates were generally lower in people aged 18-54 and steady in those aged 55 and over.
Although R, the number of people an infected person transmits the virus to, was 1.03 in England as a whole in September, infections appear to be rising in the East Midlands and London, with R at 1.36 and 1.59, the survey found. The incidence was nearly twice as high in black participants than in whites (1.41% versus 0.78%), and more common in large families, and among people who shared their home with at least one child.