Here, an embarrassed silence.
There, a sharp remark.
Often a marked annoyance.
It is an understatement to say that the iconoclast Didier Raoult was able, once again, to arouse contrasting reactions within the scientific community, after new analyzes on the coronavirus crisis.
The director of the Mediterranean Infection University Hospital Institute assured this Tuesday on CNews that he had observed "a new variant" of Covid-19, "more dangerous" than "the virus which circulated in July and August".
In the Marseille city, of which he has become the great scientific figure, the second deputy mayor, Samia Ghali, had already given credit to the idea that more or less virulent forms of virus would circulate.
“We don't have the same Covid in Marseille as in Paris, Lyon or Toulouse,” she said on LCI.
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These different declarations highlight a proven phenomenon: the mutation of Covid-19, of which different “variants” have developed since the start of the pandemic.
But virologists remain extremely cautious, not to say skeptical, when it comes to commenting on possible differences in dangerousness between these forms of the same virus.
To situate the debate, we must look at the way in which the Covid-19 is structured.
Its genome, that is to say its genetic material, comprises nearly 30,000 "base pairs": it is encoded in 30,000 characters.
Each time the virus reproduces itself, these thousands of characters are duplicated.
But sometimes mistakes do happen.
" Natural selection "
A character can be replaced by another, another removed, or inserted.
This is called a mutation.
“As a general rule, variants emerge when they propagate more efficiently in the population than the original strain,” notes virologist Yves Gaudin, from the Institute for Integrative Cell Biology (I2BC) in Paris-Saclay.
Either because they are more contagious, or because they escape a little better from the natural immunity which is created over time among the population.
It is a form of natural selection.
"
The Covid-19 is already spreading very quickly and faces no collective immunity.
Its various "variants" therefore present "small mutations, minor differences", continues the virologist.
"We are still facing the same disease: we find the same patients in the hospital with the same symptoms as in March," he said.
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"Today, it is estimated that seven major forms of virus are circulating in the world, one of which alone represents nearly 90% of strains, contextualizes Jean-Daniel Lelièvre, head of the infectious disease department of the Mondor hospital, in Créteil (Val-de-Marne).
Do these mutations interfere with the pathogenicity, i.e. the infectious capacity of the virus?
For now, we don't have much to say.
"
For Vincent Maréchal, professor of virology at the Sorbonne, the common mistake would be to think that the mutation of a virus would necessarily cause a difference in its behavior.
"If you have a text of 30,000 characters that makes sense and you change a few characters, the error does not necessarily have an impact," he illustrates.
The severely ill have not changed
Above all, it is rare to see a variant developing which is more virulent than the original strain.
"The interest of the virus is not to be more pathogenic," he analyzes.
A relatively benign virus passes silently from one host to another.
Conversely, if it becomes more virulent, people will stay at home, develop symptoms or even die, preventing the virus from reproducing.
"
Anyway, the link between mutation and virulence "must be discussed with the test of data", slices the virologist.
For example, the profile of people hospitalized or placed in intensive care should change significantly.
However, since the start of the epidemic, the most severely affected patients do not seem to have fundamentally changed: they are mainly elderly or vulnerable patients.
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“This summer, we were able to see thanks to the policy of massive tests that the virus circulated a lot in the 15-44 age group, rewinds Vincent Maréchal.
This caused, logically, few serious forms.
There, it spreads to other age groups: the disease therefore appears more clearly.
This does not mean, unless proven otherwise, that the virus has become more virulent.