A large English COVID-19 prevalence study on Wednesday found that fully vaccinated people have an around 50 to 60% reduced risk of infection from the Delta variant of coronavirus, including those who are asymptomatic.
Researchers from Imperial College London said that people who received both the shots of the Coronavirus vaccine were reported half as likely to test positive for COVID-19, adjusting for other factors like age, whether or not the people tested had coronavirus symptoms.
According to the study, the researchers focussed on those who had COVID-19 symptoms the effectiveness in them rose to around 59%. However, the study covered a period when the Delta variant completely replaced the earlier dominant Alpha variant of coronavirus.
The estimates, which did not break down effectiveness by the vaccine, are lower than those reported by Public Health England for Pfizer and AstraZeneca’s shots.
While this was not surprising or worrying according to the researchers, given that PHE estimates were based on those who have symptoms and get tested, while the Imperial study is designed to pick up more people.
Imperial epidemiologist Paul Elliot, who leads the study, told reporters that, “We’re looking at effectiveness against infection amongst a random sample of the general population, which includes asymptomatic individuals.” He added that even those who had symptoms in the study might not have got a test otherwise.
“So again, it’s a different bunch of people.”
A link between infections and hospitalisations were found in the study, which had previously deteriorated and had started to reconverge, a move that overlaps with the spread of Delta among the younger people who may not be fully vaccinated.
According to PHE, though vaccines provide good protection against severe disease Delta variant carries a higher risk of hospitalisation.
The overall occurrence of coronavirus in unvaccinated people was 1.21% which is three times higher than the 0.40% prevalence in fully vaccinated people, said the researchers. They also said that the viral load among people with coronavirus was also lower in vaccinated people.
YOUNG PEOPLE
The latest findings of Imperial’s REACT-1 prevalence survey were presented by the researchers and these findings showed there was a fourfold increase in infections in a month to reach 1 in 160 people in England.
The latest study conducted between June 24 and July 12 covered the time ahead of a peak in daily reported infections on July 17, and found that the rise was fuelled by the spread in younger people.
Imperial professor Steven Riley said that 5- to 24-year-olds reported 50% of all infections, even though they are only 25% of the population. Schools have now been closed for summer holidays, and cases have dropped from that peak despite legal coronavirus limitations ending on July 19.
Riley told reporters that, “We’ve shown that prior to the recent dip, young people were driving the infections.”
“These data support the idea that there is uncertainty about what might happen in September when schools return and we have increased indoor mixing, because of the patterns of infection that we saw driving the growth.”
