After a major study in England showed evidence of breakthrough infections three months after vaccination, scientists have encouraged eligible patients to get Covid booster shots.
Imperial College London researchers analysed over 100,000 samples from random populations and discovered that Covid infection rates among the unvaccinated were three to four times greater than in those who received two shots.
However, full vaccination did not reduce infection rates significantly. They dropped from 1.76% to 0.35% for the unvaccinated three months later to 0.76%. But infection rates rose to 0.55% to 3.5 to 6 months after the second shot.
This finding suggests that immunity to infection with or without symptoms begins to decrease several months after full vaccination. However, other studies have shown that vaccine protection against death and hospitalisation is much stronger.
Paul Elliott, who is the head of the React study, and a professor of epidemiology at Imperial, stated that the potential increase in breakthrough infections over time makes it more important to have a booster program. Prof Christl Donnelly, a statistician on the study, said that it is an incentive to people to get their booster dose as soon as they are available. These results were announced as the number of Covid cases in the UK climbed to 42,776, which is the highest level since late July.
React has used community testing to provide frequent snapshots of the epidemic throughout the Covid crisis in England. The most recent data includes results from 100.527 swabs collected between 9 and 27 September and another 98.233 swabs that were taken in June or July.
The highly transmissible Delta virus was the only virus sequenced in this study. One sample carried an E484K mutation, which could help the virus avoid immunity from previous infection or vaccination. The UK Health Security Agency is monitoring the relative of Delta.
The survey's preliminary results, which have not been peer-reviewed yet, showed that five- to seventeen-year-olds had the highest infection rates in September. About 2.5% of them tested positive. Next came 35 to 54-year olds, who are the most likely to have children. Now, efforts are underway to provide boosters for 50-year-olds as well as vaccinate healthy 12- to 15-year olds.
The study found that full vaccination decreased the risk of infection by 60%, whether there were symptoms or not. Although the Pfizer vaccine was more effective than AstraZenecas in terms of effectiveness, the vaccines were administered to different age groups at different times during the epidemic so it is impossible to compare them.
Previous studies have shown that antibodies to Covid decrease in the months following vaccination. However, new research suggests that two doses of Pfizer vaccine are highly protective against severe diseases. Two shots of Pfizer vaccine proved to be 90% effective in preventing hospitalization for at least six month, according to US researchers. However, protection against infection was only halved during the same time period.
React's survey revealed that although infection rates in England were flat in September, there were distinct trends in certain age groups and regions. The R number was 1.18 for those up to 17 years. School children were particularly at risk. The rates were steady for those 55 years and older, while they fell in the 18-54 age group.
The number of infected people who pass the virus to others, R, was 1.03 in England in September. However, it seemed that infections were increasing in London and the East Midlands. R stood at 1.36 and 1.59 respectively, according to the survey. Black participants had an infection rate nearly twice that of whites (1.41% versus 0.78%). It was also more common in large households and those who live with at least one child.