What do we know about the different variants of Covid-19?
Reuters
Text by: Simon Rozé Follow
6 min
British, South African, Brazilian or Japanese… The different variants of Sars-CoV-2 are worrying.
Responsible for an increase in contagiousness, they could also have an impact on vaccine effectiveness, even if this remains to be demonstrated.
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Sars-CoV-2, responsible for Covid-19, has
several thousand variants
.
It is a frequent and natural phenomenon.
Indeed, when the coronavirus uses our infected cells to multiply, it sometimes happens that there are copying errors: mutations.
In the vast majority of cases, they are harmless and can sometimes even be deleterious for the virus.
Unfortunately, other times these mutations can give him an advantage.
This is the case for the British, South African or Brazilian variants: copying errors allowed them to be more contagious.
The mutations have, in fact, taken place on the key that the virus uses to enter our cells: the S protein, or spicule.
This key is more efficient on these variants.
These mutations are closely watched, because beyond their impact on the progression of the epidemic, the S protein is also the target of our immune system.
► Also to listen: Variants of Covid-19 in France: "People who are carriers of the mutated virus are more likely to communicate it"
N501Y and E484K
Two mutations in particular are currently being monitored.
The first is what scientists call N501Y.
It is indeed suspected of making the coronavirus more contagious.
This mutation is present on the three variants which make the news: British, South African and Brazilian (and not Japanese, because if it is indeed
talked about in Japan
, it was imported there by travelers from Brazil. ).
Although the increase in contagiousness is proven, these variants have not, however, become resistant to vaccines.
In any case, it is not resistant to that developed by Pfizer-BioNtech, for which
in vitro tests
have made it possible to be sure.
The second mutation, however, offers potential resistance to the variants that carry it.
Named E484K, it is present on the South African and Brazilian variants, but absent from the British.
Because of it, they are suspected to be less sensitive to our body's immune response.
There are two main elements supporting this hypothesis and they have both been the subject of scientific publications which are reacting, even if they are only at the pre-publication stage.
The first describes a
case of reinfection in Brazil
.
This is a 37-year-old woman, infected for the first time in June, then a second time in October, by the variant carrying the E484K mutation.
This second contamination caused a more serious form of Covid-19.
This could be a sign that this variant was less sensitive to this woman's immune response.
The second article
relates a laboratory experiment: the coronavirus was placed in the presence of plasma from a cured patient, and therefore of his antibodies.
The goal was then to observe if, according to the natural mutations of the virus, it could become resistant to these antibodies.
The answer is yes: a variant appeared after three months.
He carried this same E484K mutation.
Resistance yet to be proven
Taken together, these elements therefore worry the community.
But for now, these are still only clues, and we do not yet have enough knowledge to say that the variants carrying this E484K mutation would indeed be more resistant.
Even if this would be the case, it remains very likely that the vaccines developed will retain some efficacy.
Several parts of the spicule are in fact targeted: if some are modified by a mutation, there will always remain others leading to an effective immune response.
Of course, the risk of the appearance of a resistant variant worries.
However, this remains to be confirmed for the moment, and there is already something to do with gray hair with the increase in contagiousness observed on these three variants.
With the "classic" coronavirus, it is estimated that it takes about 70% of the immune population to stop the epidemic, whether this immunity is acquired after contracting the disease or after vaccination.
With a more contagious variant, this proportion rises to 80%, or even more.
Finally, a virus that circulates more is also a virus that is more likely to see variants appear, some of which could be even more annoying.
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