The long haul of long Covid

Three years after the official declaration of a pandemic, 65 million people - one in 10 who had Covid-19 - still have symptoms. Some are so ill they are yet to return to work. The Economist’s health editor, Natasha Loder, examines the science behind long Covid and hears about the challenges as researchers try to unravel the cause behind a condition associated with around 200 symptoms.