he hopes the number of recognised symptoms can be narrowed down, but so much about the illness is still unknown. if we think of other viruses that are well recognised to cause persistent problems — like glandular fever, like hepatitis — they affect relatively small numbers of people. it's the size of the problem that's different this time. a recent uk survey found more than one in ten people were self—reporting with long covid symptoms 12 weeks after first being infected with covid. and one in four of this group said they were still experiencing symptoms at least a year later. two—thirds reported the condition was impacting on their ability to carry out day—to—day activities. there is still no answer to what causes the condition. many who've developed long covid didn't have a serious form of coronavirus and weren't hospitalised.