Researchers are closing in on long covid

IN THE 1890s one of the biggest pandemics in history, known at the time as “Russian flu”, swept the world. It left 1m people dead. Russian flu is now thought to have been misnamed. It was probably not influenza, but rather a coronavirus ancestral to one that now just causes symptoms described by sufferers as “a cold”. When it was new, however, few people had immunity to it, so it was often lethal. And not only that. For, as the pandemic receded, it left in its wake a wave of nervous disorders. A similar wave followed the next big pandemic, the “Spanish” flu of 1918 (which, though nothing much to do with Spain, really was influenza). One common symptom was lethargy so bad that in Tanganyika (modern-day Tanzania) it helped cause a famine because so many people were too debilitated to pick the harvest.

Something similar is happening now, with the covid-19 pandemic. A wave of what has become known as “long covid” is emerging in countries where acute cases have been falling. Formally, the condition is called “post-covid syndrome” (PCS). But even the official definition of its symptoms is fluid, because knowledge of its details is still evolving. Britain’s National Institute for Health and Care Excellence, for example, defines PCS as “signs and symptoms that develop during or after an infection consistent with covid-19, continue for more than 12 weeks and are not explained by an alternative diagnosis”. It does not, though, specify a list of such symptoms.