Two-thirds of people who have recently been infected with the Omicron variant say they have had Covid-19 before.
The latest findings from Imperial College’s React-1 study found 64.6 per cent of respondents said that they had had coronavirus in the past.
But researchers cautioned they did not know when the previous cases occurred and said that PCR tests can return positive test results for more than 90 days following diagnosis.
Meanwhile, the study authors have warned that coronavirus cases circulating among schoolchildren since returning to classrooms after the Christmas break could drive up hospitalisations in adults.
Data showed the infection rate in primary school-age children, those between five and 11, was 7.8 per cent and rising.
This compares with infection rates in adults, which were significantly lower, and stood at 2.4 per cent in people aged over 75.
Professor Paul Elliott, director of the React programme, said: “Of particular concern is that there is rapidly increasing prevalence among children now they are back at school and, compared with December, prevalence in older people aged 65 plus has increased seven- to 12-fold, which may lead to increased hospitalisations.
“It’s therefore vital that we continue to monitor the situation closely to understand the impact of the Omicron variant, which now makes up almost all infections in the country.”
More than 100,500 swab tests were conducted across England between January 5 and 20.
Infections in England may no longer be declining at the rapid rate seen in early January, the data also suggests.
Coronavirus infections declined in early January and then plateaued at a high level, with one in 23 infected during this period.
Dr Jenny Harries, chief executive of the UK Health Security Agency, said: “While case rates have slowed recently, prevalence is still high. Vaccination remains the best way to protect yourself from severe disease and hospitalisation from Omicron.
"I would urge anyone who has not done so to come forward for their first, second and third doses as soon as possible."
Health secretary Sajid Javid said it was “reassuring to see Covid infections beginning to slow” as the country lifted Plan B restrictions but urged people to “be vigilant”.
