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Why researchers still know so little about long-term covid

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Although long-term covid is a new disease, researchers still don’t know more than they do about the condition. What makes long-term covid such a difficult disease to define? And why is it only so easy to find out more about it? NU.nl asked two researchers.

In fact, long-term covid is not one disease, but a collection of complaints. Fatigue is the most common complaint, but headaches, muscle pain, shortness of breath, forgetfulness and concentration problems are also common. In addition, patients mention many other complaints.

It is impossible to say exactly how many people in the Netherlands suffer from long-term covid, especially because it is not always clear whether complaints belong to long-term covid or perhaps have another cause. “I hardly know anyone who never has a headache or is never tired. That does not necessarily have to be a long-term covid,” says Anke-Hilse Maitland-van der Zee, professor of Precision Medicine of Pulmonary Diseases at Amsterdam UMC.

That certainly does not mean that she does not take the complaints seriously, but demonstrating that certain symptoms are the result of the corona virus is very difficult, according to her. For example, it is impossible to find out whether people would have had the same complaints if they had not had COVID-19 – in other words: “We will never know for sure whether certain complaints were caused by the COVID-19”, says Maitland-van der Zee.

Deep into the cells

There are symptoms that are demonstrably caused by the virus. This concerns, for example, damage to the lungs, cardiovascular problems and blood clotting. These complaints mainly occur in ex-COVID-19 patients who have been in hospital, while the large majority of long-term Covid patients have experienced a mild corona infection at home.

Scientists do not know why some people continue to have complaints for a long time and others do not. There are, however, some theories. One is that the body has not yet completely cleared the virus and that virus particles remain for a long time deep in cells of organs. This process may leave people with symptoms for months after the infection has passed. Scientists suggest this in a pre-publication of a study that appeared early this year in Nature.

In that case, those virus particles should be found in Dutch patients with long-term covid, thought Menno de Jong, professor of Clinical Virology and long-term covid researcher at Amsterdam UMC. But in the nose, throat or faeces – “where you would expect the traces of the virus” – he found nothing in his investigations. This does not exclude the theory, because he has not been able to look into tissues. “But it does make it less likely that this plays a major role,” he says.

The body that keeps on fighting

A second theory is that the body gives an excessive and prolonged immune response to the virus. “The body continues to fight, as it were, even when the virus has already gone. You get very tired of that and we think that some of the people continue to have complaints as a result,” says Maitland-van der Zee.

What is certain, according to De Jong, is that long-term covid does not have one generic cause. “In part there will certainly be a biological cause, but long-term covid can also have a mental cause in some of the people,” he says. For example, it may well be possible that some people develop post-traumatic stress disorder (PTSD) after a severe corona infection. Depression is also a common complaint with long-term covid. For others, the problems can be physical as well as psychological.

In any case, long-term covid is not a chronic infection like a cold sore, the researchers say. This means that people with long-term covid have already had the corona infection themselves.

Distinguishing groups from each other

Because long-term covid is a mishmash of complaints and probably also causes, according to the researchers it is necessary to distinguish subgroups from each other. Different causes also require different treatments. For example, people who have difficulty climbing stairs can then receive occupational or physiotherapy, while others benefit more from medication or psychological help. In any case, there is currently no single targeted treatment aimed at long-term covid.

“The good news is that a lot of long-term Covid patients come out healthy again,” says Maitland-van der Zee. A Dutch study by De Jong, among others, published in May last year, showed that approximately 30 percent of people who experienced a mild corona infection at home still had one or more complaints after three months. Over time, most people recovered. For example, after nine months, 20 percent still had complaints. After one year this had decreased to 10 percent.

It is not clear whether a COVID-19 vaccination, including the booster shot, can ensure that people with long-term covid heal faster. Various studies contradict each other, according to De Jong. “Within a large group of patients in Amsterdam that we have been following for a long time, there does not appear to be a beneficial effect of vaccination,” he says. Conversely, vaccination reduces the risk of long-term covid, because the chance of serious infection decreases with the jab.

What is omikron doing with long-term covid?

Finally, it remains to be seen what the omikron variant will do with long-term covid. At the moment there is no meaningful word to say about this, because less than three months have passed since the mutant appeared in Western Europe.

“Because omikron appears to be less serious, you would expect the risk of long-term covid to be smaller. But given the large numbers of infections, a small risk can still translate into a lot of people with long-term complaints,” says De Jong. According to Maitland-van der Zee, it is also possible that the new variant will turn the knowledge about long-term covid upside down again. “We’ve only known this disease for a year, and it’s still changing.”

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