Coronavirus can kill, or pass through a body unnoticed. Its effects in the short term are wildly unpredictable. But as we learn to live with this new virus we’re discovering more of its grisly secrets. One of them is that the damage it does to the body in the long run might leave a dreadful legacy. This is the story – as much as we know it – of Long Covid. Reporter Giles Whittell, presenter Basia Cummings.