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What we know—and do not know—about long covid

It may actually be a collection of quite different syndromes

Doctor Nicolas Barizien examines Helen Sideropoulos-Einsargueix, a patient who has been suffering from COVID-19 symptoms for months, during a rehabilitation medical appointment at the Foch hospital in Suresnes, near Paris, France, December 8, 2020. Picture taken December 8, 2020. REUTERS/Benoit Tessier - RC28OK9SLU1K

MORE THAN two years since the start of the covid-19 pandemic, scientists have learned a lot about how the SARS-CoV-2 virus affects the body. But the symptoms and complications known as “long covid” are far less understood. America’s Centres for Disease Control and Prevention (CDC) defines long covid as the continuation of symptoms for at least four weeks after infection. The World Health Organisation says it usually occurs three months after the onset of the virus and lasts for at least two months. Fatigue, shortness of breath and brain fog are common features. There is little consensus on how to treat it. What is long covid?

The prevalence of long covid is hard to calculate and some early reports gave inflated estimates. The CDC believes one in ten Americans will develop long-covid symptoms more than a month after infection. Britain’s Office for National Statistics (ONS) estimates that 1.7m people, or 2.7% of the population, were experiencing self-reported long covid as of March 5th. Of those, 1.1m found their ability to undertake day-to-day activities seriously curtailed. Most experienced fatigue, a third had shortness of breath, and almost a quarter reported muscle aches. The condition was most common in women, those aged 35 to 49 and in people living in poor areas. Those employed in social care, education or health care were also more likely to report symptoms.

But there are problems with even these careful estimates. Fatigue and muscle ache could be caused by a number of other conditions. An earlier ONS study found that 5% of people infected with covid had at least one of 12 common symptoms 12 to 16 weeks after infection; 3.4% of a control group who had not been infected also reported one of these symptoms.

Confusingly, long covid may actually be a collection of quite different syndromes. For example, any encounter with an infectious disease can have serious long-term consequences. Covid can cause lingering or permanent damage to the lungs and heart. Some cases of long covid may really be “post-intensive care syndrome”, which can affect anyone who spends time in an intensive care unit. Sufferers face serious physical weakness, lung damage and problems with memory and attention. They may have post-traumatic stress disorder. And researchers also wonder if some cases of long covid might be a form of post-viral syndrome, like chronic fatigue. Last, some patients who appear to have long covid may in fact have a continuing infection that their immune system has not cleared.

Because so many people have caught covid, if even a tiny percentage suffer continuing health problems a huge public-health crisis could ensue. Some call it the pandemic after the pandemic. Pharmaceutical companies are pursuing trials of drugs that may help. Studies are under way with a drug called Paxlovid, which is already used to treat covid itself, as well as with other antivirals. Another trial is testing a hypothesis that the virus can impair the ability of human cells to generate energy (which would cause fatigue and muscle weakness). Some firms are looking for solutions to chronic pain, damaged lung function and cognitive defects. Besides helping long-covid sufferers, this work may benefit those with other post-viral conditions, who have long been ignored.

All our stories relating to the pandemic can be found on our coronavirus hub. You can also find trackers showing global , excess deaths by country and the virus’s .

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