Why long Covid can be really grim, but is rarer than you think

However, he said he was surprised by the other side of long Covid, namely the numbers of people, often with mild infections, reporting symptoms for weeks or months, including neurological symptoms, fatigue, and ‘brain fog’.

This isn’t new, either: many viral conditions cause post-viral fatigue (PVS), and experts aren’t entirely sure why. In some other conditions, up to 10 per cent of those infected report long-term symptoms, including those who contracted two other coronaviruses, Sears and Mers.

But despite the headlines, all of the scientists stressed that long Covid, and particularly the more debilitating elements, was not the norm, particularly for young, asymptomatic individuals. 

One study of 200 young Swiss army recruits, mainly men, published in the journal Eurosurveillance, found that none had experienced any decrease in their strength two months after infection. However, some 19 per cent had lost aerobic capacity. 

Prof Francois Balloux at University College London, who was not involved in the study, said: “The decrease in aerobic capacity in the symptomatic group is likely a mix of genuine short- and possibly medium/long-term lung damage, but also a consequence of those ill with Covid-19 not getting as much physical exercise.” 

The study is seen as particularly useful because the recruits undergo constant fitness tests so there was a baseline measurement of their fitness to compare. 

Prof Frances Williams at Kings College London, who is assessing the data behind the Covid Symptom Study app used by four million people, said this study was backed up by her team’s work. 

Researchers have found that young people are less likely to experience long Covid, and men appeared less likely than women to suffer. 

“If you are older you are more likely to have long-lasting symptoms, and unlike the risk of hospitalisation, it’s women who tend to have longer lasting symptoms than men, at least at four weeks. It’s also mainly people who had the most symptoms in the first place,” she said.

Their data, on 4,000 individuals, suggested that 13 per cent of people have symptoms after a month, 4.5 per cent at eight weeks, and just over two per cent at 12 weeks. The mean age for those suffering short-term Covid symptoms is 40, long-term is 49, and really long-term, say over three months, is 52. 

“This is absolutely the message we should give: a small proportion have symptoms at 13 weeks, but really pretty much everybody is better by then,” Dr Williams said. 

And while this is longer than some illnesses, it is not completely off the charts, researchers said. For example, glandular fever and Lyme disease can make some people ill for months, sometimes from initially mild infections. 

The app data suggests two main clusters of symptoms experienced by long Covid patients: firstly, fatigue, headache, and a loss of sense of smell or taste, and secondly, ongoing fever, abdominal upset and loss of appetite.

Older people are more likely to experience the second lot of symptoms, Prof Williams said. But she stressed that other symptoms, particularly things like depression and sleeplessness, could be harder to measure.

“We will inevitably end up describing a whole range of so-called long Covid manifestations, including the psychological effects,” she said.