Two thirds of the people infected with omicron have previously already had the Covid virus, a major new study suggests.
Imperial College London’s REACT-1 study sent out 100,000 Covid tests to people around England and asked them fill in a questionnaire.
One question is if the person taking the swab has had Covid before, and if this was confirmed with a test, or was just a suspected case.
More than 3,500 people who tested positive between January 5 and January 20 answered this question, and almost two-thirds (64.5 per cent) said they had previously tested positive for coronavirus.
A further 7.5 per cent said they suspected they had caught the virus previously, but had not received a positive test.
Prof Paul Elliott, director of the REACT programme and chairman in Epidemiology and Public Health Medicine at Imperial College London, said these can not be technically labelled as reinfections, because it is possible some cases are residual infections, where a person has simply tested positive twice for the same infection.
“They may have had a positive test for omicron, for all I know, in December, and then got tested by us,” he said.
“We don't know when they had it, it could have been in May 2020, or last week.”
It has been known that omicron is more able to infect people who have previously had Covid-19 than other variants, due to an innate ability to dodge the immune system.
As a result, reinfections have gone from accounting for a miniscule proportion of all infections, to a sizable chunk.
The latest UK Health Security Agency figures show 11 per cent of all cases were reinfections, but the new study indicates the true figure may be much higher.
However, reinfections are not included in the current daily case figures, an oversight which is now set to be corrected as the UKHSA announced on Tuesday reinfections in England will be included in daily cases from January 31 onwards.
A reinfection will be defined as a person testing positive twice, at least 90 days apart, and the daily figures will be updated back to the start of the pandemic.
Imperial’s study also confirmed that the prevalence of Covid reached an all-time high earlier this month, peaking at more than four per cent of the population, equivalent to around one infected person per 23 people.
Almost all of the positive tests detected though the study were omicron, completely replacing delta.
But throughout January, REACT detected an overall decrease in the total number of infections, and a potential recent plateau.
Sajid Javid, the Health Secretary, said: “It’s reassuring to see Covid-19 infections beginning to slow across the country, as we move back to Plan A.
“Covid-19 rates are still high so as we learn to live with the virus it is vital we continue to be vigilant – wash your hands, let in fresh air, get tested and, if you haven’t already, get boosted now.”
The study comes as figures from the Office for National Statistics (ONS) reveal deaths in England are currently 4.1 per cent below the pre-pandemic average for this time of year.
Data show there were 534 fewer deaths registered in the week ending January 14 in England compared to the 2015-2019 average.
Dr Raghib Ali, an epidemiologist and NHS consultant, said there was no evidence that the omicron wave was causing excess deaths and that it was clear many “Covid” patients in hospital were incidental cases who had been admitted for other reasons.
“Compared with previous waves, we’re no longer seeing excess deaths at the same time as Covid deaths,” he said.
“I think we’ve passed the peak of this wave on all parameters, cases, admissions and deaths. Schools have been back for three weeks now and there has been a slight uptick but I can’t see any scenario where things get worse from here.
“So it’s safe for Plan B restrictions to be removed, and there is little difference they make much difference anyway. England’s death rates are lower than Scotland, Wales and Northern Ireland despite not imposing such stringent restrictions.
“It’s fair to say that hospitals are not as busy with Covid as feared and staff absences are now improving.”