a potentially fatal runaway of the immune system

Fever, fatigue, dry cough: four times out of five, the new coronavirus SARS-CoV-2 causes "mild or moderate" symptoms. But to this is often added respiratory discomfort which can lead to a severe acute respiratory syndrome.

This is the case for about one in five or six people who requires hospitalization to get by, according to the World Health Organization (WHO).

Difficulty breathing, feeling like you have lungs in a vice, lips or faces that start to turn blue are warning signs that must lead to an urgent consultation, according to the American health organization CDC.

The aggravation of the 7th day

A majority of hospitalized patients have pneumonia severe with bilateral involvement which is the signature of the severe form of the disease, according to WHO. Often worsening arrives suddenly, about 7 days after the appearance of the first symptoms, according to Pr Yazdan Yazdanpanah, head of the infectious diseases department of Bichat hospital (Paris).

This calendar retains a large part of mystery and variability, but regularly leads to an acute respiratory distress syndrome (ARDS). This situation where the lungs do not provide enoughoxygen to vital organs requires a ventilation artificial with the use of respirator.

Cytokine shock

" Evidence is mounting to suggest that some of the patients with severe forms of Covid-19 are subject to cytokinic shock syndrome »Writes, with British colleagues, Jessica Manson, specialist in inflammatory phenomena at University College Hospital from London in the medical journal The Lancet.

This phenomenon of “hyper-inflammatory storm” has been known and described for only twenty years. He was implicated to explain the danger of two other respiratory diseases caused by coronaviruses, SARS (774 died mainly in Asia in 2002-03) and Mers (Middle East respiratory syndrome, 866 deaths since 2012).

He is also suspected of having been at work during major pandemics like the terrible " influenza Spanish ”, which killed around 50 million people in 1918-19.

Exuberant immune response

Cytokines are molecules produced by the cells of the immune system to regulate the immune action. They promote the inflammatory reaction, which is a natural defense response of an attacked organism.

But in the case of "the cytokine storm", we observe a runaway of this system which leads to a hyper-inflammatory reaction which can become lethal.

How important are these storms in the deadly cycle of severe Covid-19 cases? " That's a very good question ", Answers the American specialist in microbiology and immunology, Stanley Perlman, who studied these phenomena in the cases of Sras and Mers.

" I think an exuberant immune response is what really kills patients (from Covid-19, editor's note) by destroying tissue. But it's not a certainty "Replies to AFP this expert from the University of Iowa.

How to calm the storm?

It should be able to calm the storm in the lungs without lowering the immune functions of patients. For now, medicine is groping and mounting emergency tests as the pandemic progresses.

For example in Paris, the public hospital group AP-HP has launched in recent days the CORIMMUNO trial to Review several drugs against these excessive inflammatory reactions.

" At present, there is no effective and proven therapeutic approach against this phenomenon. "Laments Professor Perlman. The academic points out that administering corticosteroids, drugs anti-inflammatory currents, would be " for sure deleterious For Covid-19 patients.