What if cytokine storms were a misconception to explain covid deaths? According to a new study published in the journal Science Advances on November 13, this immune system runaway would actually have played a minor role in the severe forms and mortality of covid.
On the contrary, American researchers from Washington University of Medicine and the St Jude Hospital Research Center in Memphis who signed the study favor the thesis of an exhaustion of the immune system.
Read also: Two avenues to explain the serious forms of Covid
Covid or flu, what immune response?
The study is the largest comparison of the human immune response to two viral respiratory infections to date: influenza and covid-19. The research involved 168 adults with covid, 26 adults with influenza and 16 healthy volunteers. More than 90% of patients with covid-19 reported a severe form that required hospitalization and 23% of them died.
For influenza, more than half of the patients were hospitalized and 8% of those hospitalized died.
Only 4% cytokine storm
To understand the immune response, the researchers measured the levels of 35 different cytokines. Cytokines are small proteins secreted by blood cells to organize the immune response and trigger inflammation. Cytokine storms, potentially fatal immune spasms, occur when excessive or abnormally regulated production of cytokines results in hyperinflammation.
Result: only seven covid patients, or 4% of the group, presented levels corresponding to a cytokine storm. The majority, on the contrary, exhibited a very weakened immune response. And overall, the covid patients displayed lower cytokine levels than the influenza patients.
Exhaustion rather than runaway
If cytokine storms are not the cause, what is? The researchers measured that the level of certain cytokines that play a central role in the antiviral immune response, type I and II interferons, was significantly reduced.
Results which suggest a “weakened immunity“at”most covid patients“, interprets doctor Paule Thomas, specialist in immunology at the St Jude center in a press release from this establishment. “These patients may need therapy to increase their immune response in order to bring down the virus“he adds.
Indeed, these new results call into question the current use of steroids such as dexamethasone, which suppress the immune system to counter possible cytokine storms. These drugs could further weaken an already weakened immune system.
The study authors therefore suggest setting up a rapid test to measure cytokines in covid patients. This examination would identify people in whom immunosuppressive therapy – such as dexamethasone – would be beneficial and those in whom immunostimulant therapy would be preferable.