The omicron variant of Covid-19 appears less likely than delta to lead to long Covid, UK researchers say.

But because omicron is much more contagious than previous variants, the huge number of people who have been infected since it started spreading in winter means that there will still be many who will be struggling with long-lasting symptoms, such as brain fog, headaches, and wasting disorders. fatigue.

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The new research, which was published Thursday in The Lancetis an observational analysis of people who signed up for a smartphone app-led project called ZOE Covid study. Users regularly report any Covid symptoms, vaccination status and other demographic information.

Since the app launched in March 2020, around 4.7 million people, most of whom reside in the UK, have signed up.

“For each successive virus wave, we investigated whether the probability of becoming long Covid is affected by different variants,” said Claire Steves, author of the new study and clinical senior lecturer at King’s College London.

Steves and his team found no difference in long Covid prevalence when they compared the original strain of the virus to later variants up to the delta.

“We were really excited when omicron came along, especially because it moved through our population very, very quickly,” Steves said. “We wanted to know as soon as possible what this meant for a long time Covid.”

The researchers focused on data from 41,361 adults who tested positive for Covid-19 between June 2021 and the end of November 2021 – when the delta variant was dominant – comparing them to 56,003 adults who tested positive after the taking omicron between December 2021 and March 2022, when over 70% of cases in the UK were estimated to be omicron.

Long Covid is defined by the UK team as having new or persistent symptoms at least one month after initial infection.

Nearly 11% of those infected during the delta period met the criteria. When researchers looked at those infected during the omicron wave, the percentage of long Covid patients fell to 4.5%.

All participants had been vaccinated before their infection. Some research has suggested vaccines may offer little protection against long Covid.

When Steves and his team took vaccination status into account, they continued to see a reduction in long Covid risk during the omicron wave. “It’s a solid conclusion,” Steves said.

The research does not, however, provide details on how long people experienced Covid or the severity of symptoms.

“This is important data,” said Andrea Lerner, a physician at the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health. She is affiliated with a major long Covid study called RECOVERwhich aims to recruit at least 18,000 people.

“But what it doesn’t tell us are the clinical details of what they’re going through or how long they’re having symptoms or effects,” Lerner said.

Rise in long Covid cases

There are no definitive data on how many people are likely to have Covid for a long time. Estimates generally fall into the range of 20% to 30% of all Covid infections.

Even though omicron is less likely to cause lasting symptoms, especially for people who have been vaccinated, the actual number of people affected by long Covid is not decreasing, Steves said.

“Actually, it’s going up,” she says.

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Since the UK report tracked infections when the omicron BA.1 version was dominant, it is not yet clear whether the new subvariants BA.2.12.1 and BA.4 and BA.5who gain a foothold in the United States, will lead to more or less long Covid symptoms.

Long Covid clinics in the United States, which are currently averaging more than 100,000 cases a day, according to NBC News data, are seeing many new patients who have recovered from omicron and are still presenting with a range of symptoms.

“We saw infected patients in December, January and February in our clinic,” said Dr. Upinder Singh, professor of infectious diseases and division chief of infectious diseases at Stanford Medicine in California.

But while the ZOE app can collect user-focused data in real time, a backlog of long Covid appointments makes it difficult for doctors treating long Covids to know whether patients were infected during delta waves or omicron.

“I don’t have the numbers to know if it’s more or less than after delta, to be honest,” Singh said. “We are planning so far.”

Dr. Greg Vanichkachorn, an occupational medicine specialist at the Mayo Clinic in Rochester, Minnesota, said his team is also seeing long Covid patients who were infected during the omicron wave.

“While the omicron variant may have less risk for long Covid, the large number of people with omicron means there may be a rapid increase in long Covid cases around the world,” Vanichkachorn said.

“Long-haul Covid continues to be a public health issue that needs to be addressed,” he said.

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