Two-thirds of people infected with the Omicron variant have had COVID-19 before, a study has found.

In an ongoing analysis of more than two million people across England since March 2020, researchers found 65 per cent of them had previously tested positive for coronavirus.

Findings by Imperial College London’s React study, published on Wednesday (British time), come from 100,607 PCR test results, with swabs collected from January 5-20.

About 4000 people, including British healthcare workers, volunteers and households with children, were infected during this period.

The rate of positive results is England’s highest since the beginning of the pandemic and subsequent study.

“Of those who reported whether they had a history of COVID-19, almost two-thirds (64.6 per cent) of infections were in people who reported confirmed prior COVID-19,” React research says.

Trends in the data suggest that infections rose sharply between these two study periods. Photo: Getty

However, the legitimacy of the reinfections has been questioned, after researchers amended documents following a BBC article about the damning results.

It is uncertain how many were true reinfections, given the study required people to provide results voluntarily.

“These results are based on self-reported data and therefore it’s uncertain what proportion of these are reinfections or recent infections picked up due to the sensitivity of PCR testing,” React said.

CNBC reported before the amendment that researchers had found an additional 7.5 per cent of infected participants said they had previously contracted the virus, but that it was not confirmed with a PCR test.

Other estimates by the British government suggest one in every 10 Omicron cases are possible reinfections.

It was also unclear how many of those who tested positive had been fully vaccinated.

More than 102,000 positive tests were reported in Britain on January 26.

Imperial College London’s findings in December estimated that the risk of reinfection with the Omicron variant was 5.4 times higher than that of the Delta variant.

“This implies that the protection against reinfection by Omicron afforded by past infection may be as low as 19 per cent,” researchers said.