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Why long Covid is much less common in new cases

The risk of getting long Covid when infected with the virus is just a tenth of what it was at the start of the pandemic, according to scientists tracking the virus.

Imperial College London’s REACT study found a combination of immunity built up from previous infections and vaccinations – and the fact that the virus is less severe now than it was earlier in the pandemic – have contributed to the declining risk.

About 2.8 per cent people who have caught the Omicron variant of Covid have gone on to develop long Covid, defined as having symptoms for 12 weeks or more.

Omicron has been dominant in the UK in various mutations, or subvariants, since January 2022. These have a variety of names – such as Pirola, or BA.2.86, Arcturus (XBB.1.16) and Kraken (XBB.1.5) – all of which have descended from the Omicron variant.

That compares to just over a fifth with the original, “wild type”, strain of Covid, 13.8 per cent for the Alpha variant and 9.3 per cent for Delta, according to the Imperial scientists, who have been monitoring Covid since the start of the pandemic.

“We find that compared to wild type virus, those infected when Omicron was dominant were far less likely to report symptoms lasting beyond 12 weeks,” said Christina Atchison, of Imperial College London.

“This may reflect the changing levels of immunity in the population from previous exposure to the virus and vaccination,” she added.

Professor Helen Ward, also of Imperial College London, added: “We show that people with Covid during the time when Omicron was dominant were 88 per cent less likely than people at the time of wild-type to have persistent symptoms of 12 or more weeks.”

Asked if the waning severity of Covid also played a role in the length of the symptoms, she said: “We can’t unpick this from our data, but we know that severity of initial Covid-19 symptoms is strongly associated with risk of persistent symptoms, and that people report less severe symptoms with more recent variants which may be due to a combination of past infection, vaccination and possible lower severity of the variant itself.”

The study, part of the government-backed REACT series, finds that long Covid is still a big problem affecting tens of thousands of people.

But the proportion of people now being affected by new Covid cases has fallen significantly.

The findings in the new research come from a representative sample of more than a quarter of a million people in England surveyed as part of the ongoing REACT study.

It found that the most common lasting symptoms were mild fatigue, difficulty thinking or concentrating and joint pains.

But other persistent symptoms reported included loss or change of sense of smell or taste, shortness of breath, severe fatigue, chest tightness or pain, and poor memory.

People were more likely to report symptoms for a long time after their initial infection if they were female, had severe initial symptoms, were infected earlier in the pandemic, or had pre-existing health conditions.

The study also found that the percentage of people who recovered after 4 to 12 weeks fell from 12.7 per cent at the start of the pandemic to 3.4 per cent with the Omicron variant.

Meanwhile, the proportion who had recovered after four weeks has fallen from 66.9 per cent to 93.7 per cent – meaning just over 6 per cent now have symptoms that last for longer than a month.

In the latest analysis, the team collected follow up survey responses from 276,840 adults in England who registered for the REACT study. Of these, 59 per cent reported testing positive for Covid between 2020 and late 2022.

Analysis shows the average duration of symptomatic illness was around 10 days, but 1 in 10 people in the study reported symptoms for more than 4 weeks, 1 in 13 for more than 12 weeks, and 1 in 20 for more than a year. The analysis showed that almost a third of people reporting symptoms at 12 weeks will have recovered within a year.

However, while the rate of new long Covid cases appears to be falling there are still vast numbers of people who continue to have long Covid, many of whom have been suffering symptoms for well over a year, scientists said.

Estimates of how many people in the UK have long Covid vary from around 1 to 2 million.

The findings are published in the journal Nature Communications.

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