The Delta Plus variant is more likely to cause Covid infections that show no symptoms compared to the Delta strain, according to new research.
Officially called AY.4.2, scientists say Delta Plus is more likely to result in cases that show no symptoms.
The new research also shows that Covid was was just as prevalent in the UK from mid-October to early November as it was in January during the second wave.
School-age children and teenagers had the highest rates of infection of up to over five percent.
Imperial College London's React-1 study analysed swabs more than 100,000 swabs in England taken from October 19 to early November 5.
The prevalence was 1.57 percent – the same as January – compared to 0.83 percent in September.
According to the data, prevalence increased between rounds 14 and 15 of Imperial College London’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 percent in those aged 5 to 12 and 5.21 percent 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.4.2, which the scientists say is more likely to result in asymptomatic infection.
Christl Donnelly, professor of statistical epidemiology at Imperial College London, said: "It 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.
"It is asymptomatic transmission that really can make the difference between what’s relatively easily containable and what needs vaccination."
The AY.4.2 mutation which officials are monitoring as a "variant under investigation" represented 11.8 percent of infections.
In Scotland, Nicola Sturgeon has said the Delta Plus variant is being monitored after a rise in infections last month.
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.
