Covid-19 infections are finally starting to drop in the young but rates are still surging in over 55s.
The REACT study of 100,000 random swab test results showed rates overall are still highest in unvaccinated five to 11 year olds with one in every 11 testing positive between March 8 and 31.
Scientists warned the BA.2 subvariant - known as Stealth Omicron - is reinfecting some people who had been infected with the original BA.1 Omicron variant.
They estimated that one in every 12 over 55 year olds had the virus as of March 31 and this was still rising.
It comes as Covid-19 hospitalisations topped 20,000 and reached their highest level since January 2021.
REACT director Prof Paul Elliott, of Imperial College London, said: “These are absolutely unprecedented high levels, particularly the older people.
“BA.2 replacing BA.1 has led to a further peak during March following the peak in January.
“We still see prevalence rising in the oldest age groups and they’re the ones most likely to get severely ill with Covid-19.
“And we also know that hospitalisations with Covid-19 in England have been increasing in recent weeks.”
Co-author Prof Christl Donnelly said: “We don’t yet know when we’ll see a peak in the in the oldest age group and because those people are at higher risk of severe outcomes, that is a particular worry.”
Infection rates are starting to drop in under-18s and are plateauing at a high level in 18 to 55 year olds.
Despite record high infections the monthly REACT surveillance study is now being scrapped after its Government funding was withdrawn.
Prof Elliott said: “Clearly we are disappointed that we’re not going to be in the field anymore, but that’s how it is.”
Latest data shows there were 20,398 people in UK hospitals with Covid-19 on Monday.
This is the highest since the January 2021 surge when 39,256 tested positive on wards. The number in hospital reached 20,050 in January 2022.
Prof Elliott added: “I think [rising cases in older adults] is down to a combination of people mixing more... and some waning of booster protection against infection.
“Although we do know that with the booster there is still very good protection against severe illness.”
