Long Covid: two mechanisms to explain it

Four and a half years after the appearance of the coronavirus, an immense research effort has been made, which reveals several mechanisms which maintain the symptoms of covid long, weeks, even months after infection. The first clinical trials are beginning.

With Mathilde Fontez, editor-in-chief of the scientific magazine Epsiloon, we are talking, 4 and a half years after the pandemic, 2 years after the appearance of the first cases, this chronic form of covid, which we call long covid.

franceinfo: Researchers studying this disease are beginning to understand its mechanisms…

Mathilde Fontez: Yes, it’s been a long road to get here. We must remember that when the first cases of long covid appeared in 2020 – these patients who weeks, even months after infection, returned to consult because they were tired, because they had headaches, hard to think. When these cases appeared, it was initially thought to be psychosomatic. It was thought to be trauma from the infection that was lingering, but with no real underlying cause.

Except that given the multitude of cases and the severity of the symptoms, a major research effort was launched. Today, we know that long covid affects 10 to 20% of people who have been infected with covid. It is estimated that the disease affects 2 million people in France and 65 million worldwide. And, finally, two mechanisms have been discovered to explain it.

Is it linked to the presence of the virus which remains in the body after infection?

In fact, not directly: what is emerging is rather an immune dysregulation, which lasts after the infection. The first of these mechanisms was discovered by a team from the Zurich hospital, in Switzerland. The researchers analyzed the patients’ blood cells, and discovered at the end of 2023, a modification of the proteins linked to an immune pathway, called the “complement system”.

The researchers saw that this system remains activated after the end of the illness, which would explain many of the symptoms of long-term covid, such as exhaustion, fatigue after exercise, and difficulty concentrating.

And the second mechanism?

It was a team from the University of Pennsylvania in the United States who observed a generalized drop in serotonin levels in the body – again, from the analysis of patients’ blood. This drop is explained in particular by hyperactivity of platelets, and it causes disorders in brain functioning, which could be at the origin of the feeling of depression and exhaustion.

Enough to start launching clinical trials, to try to target these two mechanisms. Around fifteen trials have started – none in France at the moment – ​​with treatments different from those used for acute covid: for example, with antidepressants, to re-regulate serotonin.

In short, it’s starting: we’re starting to understand long covid. And these discoveries also shed light on how our immunity works: how the body reacts to an infection, months later. What is a cure, even beyond covid: since we also discover symptoms after other infections, such as the flu, or even the common cold.