Some people who have had Covid-19 are still experiencing lingering symptoms weeks, months or as much as a year after infection, even if the illness was a mild case. Scientists, physicians and patients have dubbed the condition long Covid.
The World Health Organization in October defined long Covid as a condition in people with a probable or confirmed case of Covid-19 three months previously, with symptoms that last at least two months and can’t be explained by another diagnosis.
Researchers and doctors are exploring several theories. One posits that a dormant reservoir of virus is lodged somewhere in the body that periodically gets reactivated, causing symptoms. This could explain why some patients experience relapses after feeling better for a time.
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Another theory is that traces of the virus are present in tissues, triggering an immune response that causes inflammatory symptoms. And finally, another theory is that some patients’ immune systems go into overdrive and mistakenly start attacking their bodies’ cells.
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An October meta analysis in the Journal of the American Medical Association examined 57 studies including more than 250,000 Covid-19 patients. About 54% of Covid-19 patients still had symptoms six months or more after infection.
