The proportion of young people at secondary school who have coronavirus has increased to one in 15, new figures show.
The Office for National Statistics said rates have increased for those in school Years 7 to 11, people aged 35 to 49, and those aged 70 and over.
The percentage testing positive decreased for those in school Year 12 to age 24, while the trend was uncertain for all other age groups, it added.
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Around one in 15 children in school Years 7 to 11 are estimated to have had Covid-19 in the week to 2 October – the highest positivity rate for any age group and up from one in 20 the previous week.
But while the number of people testing positive for the virus is estimated to have increased in England, it has fallen in Scotland and Northern Ireland.
Around one in 70 people in private households in England had Covid-19 in the week to 2 October, up from one in 85 the previous week, according to the Office for National Statistics (ONS).
'Notable increase' in Covid cases in secondary school students
One in 70 is the equivalent of about 786,300 people.
At the peak of the second wave in early January, around one in 50 were estimated to have coronavirus.
Positivity rates for the over-70s were still low at one in 170, but this is up from one in 190 the previous week.
Sarah Crofts, head of analytical outputs for the ONS Covid-19 Infection Survey, said: “There is a mixed picture of infection trends across the UK once again, with the largest increase seen in England.
“This has been largely driven by a notable increase among secondary school pupils, likely reflecting their return to school in September.”
The percentage of people testing positive for Covid-19 is estimated to have increased in all regions except the East of England, where the trend is uncertain, the ONS said.
Yorkshire and the Humber and the East Midlands had the highest proportion of people of any region likely to test positive for coronavirus in the week to 2 October, at around one in 55.
London and Eastern England had the lowest rates at around one in 90.
In Wales, around one in 55 people were estimated to have had Covid-19 in the week to 2 October, unchanged from the previous week and still the highest since the week to 23 December 2020.
In Northern Ireland, the latest estimate is one in 130, down from one in 65 the previous week, and for Scotland it was around one in 60, down from one in 55 the previous week.
The figures come after the latest Department for Education figures showed that more than 200,000 pupils were off school for Covid-related reasons last week.
This included 100,000 pupils who tested positive for the virus and another 84,000 suspected cases.
Earlier this week school leaders called on education secretary Nadhim Zahawi to set out what action he was going to take to tackle the "grim" Covid figures.