How many people still have long COVID?

The number of people affected by Long Covid has been hard to put a finger on. Some studies suggest that it might be as high as one person in five, others suggest lower. This week, the Journal of the American Medical Association - JAMA - has published a massive study considering data from more than a million people worldwide to try to get at the answer to this question. Chris Smith spoke to the lead author of that study, the University of Washington’s Theo Vos…

Theo - At the start of the pandemic, early reports came out of people who had become infected and did not recover within weeks as we would expect, but kept having problems going on for months after their illness. First thing we did was look at published studies, but we struggled to make sense out of all these different reports because they largely concentrated on counts of symptoms rather than really saying, you know, how severe is this and how does this affect people's health overall? So we turned to people who had registered to study long COVID and asked if they wanted to collaborate with us so that we could in much greater detail with information on each individual that they followed up, determine what the true extent is of long COVID.

Chris - Do we have an actual definition of what constitutes long COVID?

Theo - No, that is one of the problems. And so what we decided was, uh, rather than doing this sort of, you know, just reporting counts of symptoms, we said, Okay, well what are the big ones? And we concentrated on three large clusters of symptoms. One is people who have ongoing fatigue, often with bodily pains, you know, all over the body and mood swings. The second were people with ongoing breathing problems and then a third cluster of people with cognitive problems, you know, memory loss, lack of concentration, what, you know, popularly has been labeled brain fog.

Chris - And does a person have to have all of those things? Some of those things. One of those things. What do they need to have to fit the definition for what you are calling long COVID?

Theo - A person qualifying for one of the three clusters would be labeled as having a long COVID. But what we found was that of all the people who had at least one of these symptom clusters, about a third had more than one cluster and, you know, some unfortunate people had all three of the clusters.

Chris - And how long did they have to have had those symptoms for, for them to fit your definition?

Theo - We used the WHO definition, which says that you start counting someone as having long COVID at three months after the start of infection.

Chris - And how many independent studies did you end up collaborating with and what number of patients did that sum to? So what's your sample size here?

Theo - Yeah, so we had 10 collaborating studies, one in Russia and one in Iran. We complimented that with 44 published studies and two large medical record databases in the US. The strength of that is that you have large numbers and you can compare with controls. Because what's important with long COVID is that all those symptoms are pretty common generally. So to truly define what the occurrence is of long COVID, you have to have some comparison with people who have not been infected, where people reported how different they were with all their symptoms compared to the situation before they became infected.

Chris - So you have tried to capture and get at that problem, which is many people have said, 'well, are we comparing genuinely apples with apples the before and after COVID you'? When you do that, what trends emerge then? What fraction of people and who gets it and who doesn't? And what general predictors are there in terms of who's at risk?

Theo - Women are much more likely to be affected at twice the rate. Children are affected at half the rate of adult men. Overall our estimate is that just over 6% develops these three major long COVID clusters, but at a higher rate in women than in men and lower again in children.

Chris - And did you manage to find anything that would be some cloud with silver lining? Good news for people who have this were people by and large getting better.

Theo - Our best estimate is that 15% still have ongoing symptoms at one year. So the good news there is that the vast majority of people recover. Now what happens with that tail end? And that's still many millions of people and we only have information out going out one year past infection, We don't know how many of them will have a very chronic course of the illness. Time will need to tell. But at least for many people who become a case of long COVID, there's a reasonable chance that people will recover. The severity though of these symptoms is pretty high. You know, in our burden of disease work, we have the so-called 'disability weight' where we give a value to the severity of all the different, uh, diseases and, and their consequences. And if we take the average severity of people with these three long COVID clusters, it is equivalent to the amount of health loss that we estimate for things like deafness and the long term consequences following moderate to severe traumatic brain injury. So not trivial amounts of disability. And this is still the average. There's a spectrum of people who are way worse off and are extremely disabled and people who are less disabled that make up that average.