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A sign at a COVID-19 testing centre in the Shoreditch area of London, on May 18.HANNAH MCKAY/Reuters

Researchers in Britain have estimated that up to one in seven teenagers who catch COVID-19 still have related symptoms three months after becoming ill.

The study, by a group of scientists from University College London and Public Health England, is the largest yet to examine “long COVID” – a term for when coronavirus symptoms appear to last for months or longer – in young people. The researchers regularly surveyed nearly 7,000 children between the ages of 11 and 17 in England. Roughly half of those surveyed had tested positive for COVID-19 and the remainder tested negative.

The researchers found that after 15 weeks, 30 per cent of those who tested positive still had three or more symptoms of the disease, including headaches, tiredness and loss of smell or taste. That compared with 16 per cent of those who tested negative for COVID-19. Around 13 per cent of those who were ill had five or more symptoms – which also included dizziness, fever, chills and a persistent cough – compared with 6 per cent for those who tested negative.

Based on the results, the researchers estimated that up to 14 per cent of children who contract COVID-19 would likely develop three or more symptoms associated with long COVID, and up to 7 per cent would have five or more symptoms.

Terence Stephenson, a professor of child health at UCL who led the study, said the findings were lower than some previous estimates. “At the height of the pandemic last December, people were describing up to 51 per cent of teenagers who caught SARS-CoV-2 of having long COVID,” Dr. Stephenson told a media briefing on Wednesday. “I’m reassured that it’s nowhere near what people thought in the worst-case scenario. But I remain very concerned that there will be young people who, even if the numbers aren’t huge, they themselves are very severely affected.”

He added that even under a best-case scenario, where only teenagers who had symptoms responded to the survey and those who didn’t respond had fully recovered, there would still be a significant number of children with multiple symptoms. If that were the case, at least 4,000 children in England who caught COVID-19 between September, 2020, and March, 2021, would still have had three or more symptoms 15 weeks later. However, the total number could be as high as 32,000 based on the study’s findings. To put the figures in context, there are about 11 million teenagers in England.

“It’s not anything like the worst predictions,” Dr. Stephenson said. “But equally we’re trying to be honest and say it’s not of trivial importance. Having somewhere between 4,000 and 30,000 teenagers in England with three plus symptoms 15 weeks later is something to take very seriously.”

He added that the researchers plan to conduct follow-up surveys for several more months to analyze how long the symptoms persist and determine whether the Delta variant has had an effect. The initial surveys were taken in 2021 between January and March, when the Alpha variant was dominant in the United Kingdom. It has since been overtaken by Delta.

Unlike Canada, Britain has yet to approve vaccinations for children under the age of 16. The government has indicated a willingness to inoculate all children over the age of 12, but it’s waiting for a recommendation from a health advisory group called the Joint Committee on Vaccination and Immunisation.

Liz Whittaker, a lecturer in pediatric infectious diseases at Imperial College London who co-authored the study, said it wasn’t clear whether vaccines would prevent long COVID in children. “It’s really difficult to make decisions about vaccination in the context of long COVID because we know so little about the pathogenesis of long COVID. Long COVID in children isn’t something that follows severe disease and vaccination prevents severe disease.”

One of the study’s other findings was that around 40 per cent of both those who tested positive and those who tested negative said they felt worried, sad or unhappy. The researchers said the results likely reflected the stress many young people felt about the loss of a normal routine and social isolation because of the pandemic.

“I do think that within the population of children there may be some who are at higher risk of developing mental health difficulties,” said Isobel Heyman, a child and adolescent psychiatrist at Great Ormond Street Hospital for Children in London. She added that the surveys showed that older teenaged girls and children with pre-existing mental-health issues appeared to be the most at risk. “There’s definitely going to be a need [for treatment],” she added. “I think we just need to follow this group forward.”

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