Scientists have urged eligible people to receive Covid booster shots after a major survey in England found evidence of “breakthrough infections” more than three months after full vaccination.
Researchers from Imperial College London analyzed 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 injections.
But while full vaccination substantially reduced infection rates, from 1.76% in the unvaccinated to 0.35% in the three months after the second dose, infection rates rose again to 0.55% among three and six months after the second injection.
The finding suggests 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 breakthrough infections over time reinforces the need for a booster program,” said Paul Elliott, director of the React study and professor of epidemiology and public health medicine at Imperial. “It is an incentive for people to receive their booster dose when it is available to them,” added Professor Christl Donnelly, a statistical epidemiologist on the study. The results came as new Covid cases in the UK rose to 42,776, the highest on record since the end of July.
The React study has used community testing to provide regular snapshots of the epidemic in England during the Covid crisis. The most recent data includes results for 100,527 swabs provided between September 9-27, and a further 98,233 swabs taken in June and July.
All viruses sequenced in the study were the highly transmissible Delta variant, with a sample carrying a mutation called E484K that can help the virus evade immunity from past infections or vaccines. Delta’s relative is being monitored by the UK Health Security Agency.
Preliminary results of the survey, which have not yet been peer-reviewed, show that the highest infection rates in September were among youth ages 5 to 17, with approximately 2.5% positive results, followed by those aged 35 to 54. the age group most likely to have children in school. Efforts are underway to vaccinate healthy children aged 12-15 years and provide boosters for those aged 50 and over.
According to the study, full vaccination reduced the risk of infection, with or without symptoms, by about 60%. Pfizer’s vaccine appeared to be more effective than AstraZeneca’s, but the vaccines were given to different age groups at different points in the epidemic, so they cannot be directly compared.
While previous studies have shown that antibodies to Covid decrease in the months after vaccination, recent work suggests that two doses are highly protective against severe disease. Last week, American researchers reported that two injections of the Pfizer vaccine protected 90% against hospitalization for at least six months, although protection against infection was cut in half during the same period.
The React survey shows that while infection rates in England were largely unchanged in September, the overall picture masks different trends in certain age groups and regions. Infections were increasing dramatically in school-age children, with the R number at 1.18 in those up to 17 years old. Rates generally decreased in people ages 18 to 54 and were stable in people 55 and older.
Although R, the number of people to whom an infected person typically transmits the virus, 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 survey. . The infection rate was almost twice as high in black participants as in whites (1.41% vs. 0.78%), and more common in those in larger households and among people who shared a home with others. minus one child.