Covid-19 infections in England among children aged 5 to 11 have surged to three times the rate found in the general public, a government-funded study has found.
Data taken from 97,000 volunteers from November 23 to December 14 showed 4.47 per cent of pupils aged five to 11 had the virus compared with 1.41 per cent in the country overall.
The React-1 study, conducted jointly by Imperial College London and polling company Ipsos Mori, forecast that Omicron cases would supplant those of Delta more than three times as quickly as its predecessor overtook Alpha.
Another new study showed Omicron is less likely than Delta to cause illness requiring hospital admission.
Experts conducting the React study said the government’s decision to offer vaccines to children aged 12 and up, plus its booster campaign, may have curbed infection rates among other age groups.
The prevalence of the virus in children aged 12 to 17, previously the worst-affected age group, more than halved.
Among those aged 75 and older, it dropped by about two thirds.
The results came after the UK declared more than 100,000 coronavirus infections in a single day on Wednesday, the highest figure on record.
Prof Paul Elliott, who led the study, said the findings showed the R value – the average number of people infected by a positive case – began rising at the beginning of December.
Viral sequencing data up to December 11 showed that 11 of 650 cases were the Omicron variant and the rest were Delta.
“From December the proportion of samples which are Omicron has been rapidly increasing, reflecting both the replacement of Delta by Omicron but also the rapid rise in Omicron,” Prof Elliott said.
The study showed the spread is most rapid in London, where the R value started at an estimated 1.41 overall but rose later in the month to 1.62.
Prof Elliott said the odds of an infection being Omicron instead of Delta were estimated to increase at a rate of 66 per cent a day, 3.5 times the rate at which Delta outpaced Alpha.
Prof Elliott said it became clear to researchers that vaccinating children was having an effect on infection rates in their age group.
He said a “good proportion” of children over 12 who took part in the study had been vaccinated against Covid, and this age group had lower cases than primary school children.
“Very interesting, what we saw from our previous survey which ended on November 5 to the current survey, which was between November 23 and December 15, we saw a drop by about half in the infection rate in the older schoolchildren,” he told Sky News.
“But the youngest children that you’re talking about, their prevalence remained about the same, about 4-5 per cent.
“So we do see the real benefits of the vaccination programme in those older schoolchildren coming through in the data that we’re collecting.”
The Joint Committee on Vaccination and Immunisation updated its advice after the UK’s Medicines and Healthcare products Regulatory Agency found the Pfizer-BioNTech shot was safe for five to 11-year-olds after a robust review.
A low-dose version of the vaccine has been approved for those aged five to 11 who are in a clinical risk group, or who are a household contact of someone of any age who is immunosuppressed. They should be offered a primary course of vaccination, typically two doses.
“The results reported in this round of React show that Omicron is spreading rapidly in England and especially in London, which now has the highest prevalence of Covid in the country,” Prof Elliott said.
“Compared to the Delta variant, the proportion of Omicron cases is increasingly rapidly.
“The positive news is that both the teenage vaccination and booster programmes have already shown encouraging results, with prevalence amongst 12 to 17-year-olds and those aged 65 and above dropping significantly since the beginning of November.”
Health Secretary Sajid Javid welcomed the React-1 findings, saying they offered “yet more evidence that boosters are vital in protecting us from the Omicron variant”.
“While infections may be rising rapidly across the country, you can protect yourself, your friends, family and community by getting boosted now – like 28 million others across the UK so far,” he said.
