Coronavirus rates in England are similar to what they were in January this year, just after the peak of the second wave, new data suggests.
During mid-October to early-November 2021, the prevalence was 1.57% â€“ the same as January â€“ compared to 0.83% in September.
According to the data, prevalence increased between rounds 14 and 15 of Imperial College Londonâ€™s React-1 study across most age groups, and regions.
During round 15, which ran from October 19 to November 5, there was a fall in prevalence from a peak at around October 20 to 21.
School-aged children had the highest rates of infection with a prevalence of 4.95% in those aged 5 to 12 and 5.21% in those aged 13 to 17.
The data suggests all of the cases were the Delta variant or sub-lineages. The most prevalent was AY.4, which the scientists say is more likely to result in asymptomatic infection.
Christl Donnelly, professor of statistical epidemiology, Imperial College London, said: â€œIt is absolutely the case that if people are waiting for symptoms to do a test and to therefore identify that they are infected, and therefore cut back their contacts, being asymptomatic may facilitate transmission for example.
â€œIt is asymptomatic transmission that really can make the difference between whatâ€™s relatively easily containable and what needs vaccination.â€
The AY.4.2 mutation which officials are monitoring as a â€œvariant under investigationâ€ represented 11.8% of infections.
Researchers say the observational nature of survey data and the relatively small proportion of unvaccinated adults calls into question the comparability of vaccinated and unvaccinated groups.
However, they found that third vaccine doses for eligible adults and the vaccination of children aged 12 and over are associated with lower infection risk.
The researchers say they should therefore remain a high priority â€“ with possible extension to children aged 5-12 years â€“ and this should help reduce Covid transmission over the winter.