• As fear grows around the Indian variant and additional restrictive measures are in force in France, the Prime Minister assures us, the Brazilian and South African variants are regressing.

  • But with effective vaccines against the historic strain of the coronavirus and against the British variant, but variably less protective against the other variants, the question arises of the risk of their next spread in France.

  • A few days away from a gradual deconfinement,

    20 Minutes

    questioned Jean-Stéphane Dhersin, scientific deputy director of the National Institute of Mathematical Sciences of the CNRS.

    According to whom the respect of the barrier measures promises to be particularly decisive to avoid the propagation of these variants.

Very few “variants (South African and Brazilian)” and which “tend to regress”?

This is what Jean Castex said on Sunday during a trip to Roissy airport to see the implementation of the new protocol for travelers from five countries at risk: Brazil, India, South Africa, Argentina and Chile.

If the Brazilian and South African variants represent a minimal part of the contaminations, they remain a source of concern.

At the same time, the fear of seeing the spread of the Indian variant, which is causing a major epidemic outbreak in India, is also frightening.

For the moment, it is the English variant which is dominant in France, and all the anti-Covid vaccines available make it possible to become immune to it.

The other variants would cause an immune escape.

Could they win in France?

"The more people there are vaccinated and immunized, the more the variants favored by the immune escape will have an advantage," explains

20 Minutes 

Jean-Stéphane Dhersin, Deputy Scientific Director of the National Institute of Mathematical Sciences of the CNRS, specialist in epidemic modeling.

All anti-Covid vaccines are effective on the historical strain and on the English variant. Protection is less against other variants, but messenger RNA (mRNA) vaccines are more effective than viral vector vaccines. Is there a risk that the Brazilian, South African or Indian variants will prevail in France?

The virus mutates all the time, especially when there is a high rate of spread. Sometimes a mutation will have an "advantage" over the previous strain and will spread faster. This may be a transmission benefit: it will spread more easily because it is more virulent, or the person is infectious for longer. This is the case with the British variant, about 1.5 times more contagious than the historic strain. If it had appeared at the start of the pandemic in early 2020, when the strain at the time had a reproduction rate (R) equal to 3, this one would have had an R of 4.5.

Vaccination lowers this R which, at the same time, also decreases due to barrier measures. The latter variants have an advantage due to immune escape: they are less sensitive to the immunity acquired by disease or vaccination. Here, the R drops mainly because of the barrier measures.

The variants which dominate, as we see today with the English variant, are rather those which have a superior transmissibility advantage.

But as people get vaccinated, and the vaccination coverage of the population will be sufficient to achieve herd immunity, the R of the British variant will drop;

we will therefore probably take less strong barrier measures.

It is then possible that immune-escaped variants, unresponsive to vaccination, will prevail and cause a new epidemic outbreak.

Hence the importance of having an intelligent genomic surveillance plan.

India is experiencing a major epidemic outbreak due to the Indian variant, which is also already present in Europe.

Is there a risk of seeing it arrive in France?

There is a good chance that there will be, at some point, a few cases of the Indian variant in France, as we have seen with the Brazilian and South African variants.

These annoying variants can arrive in France when the incidence rate is high, which is the case today: there must be more than 50,000 contaminations in France every day, between the cases detected and those which are not reported. day.

And mathematically, there is a much greater risk of these variants appearing and spreading in France if you have 50,000 daily cases than if you only have 5,000.

With variants at risk of immune escape, what strategy to adopt with the various anti-Covid vaccines?

One thing is certain: it is a high incidence rate which increases the risks of the variants spreading.

However, vaccination with the viral vector sera from AstraZeneca and Janssen makes it possible to lower the incidence rate, thus minimizing the risk of immune escape.

Vaccinating massively today - while the British variant represents 85% of contaminations -, with all the types of vaccines available, makes it possible to extinguish the global fire.

So the urgency is to lower the incidence to reduce the risk of immune escape.

And to have the possibility of one day lifting the restrictive measures and returning to a "normal" life.

If the population is less immunized by vaccination against these problematic variants, is there not a risk of epidemic resumption at the time of deconfinement?

We do not know how to measure this risk of epidemic resumption because in concrete terms, there are on the one hand the measures recommended by the authorities, and on the other the way in which they will be applied.

We saw, at the end of the first confinement in France, that the incidence rate continued to drop, because people continued to be careful.

There, we do not know if at the reopening, they will remain cautious or relax, we will have to follow these parameters closely.

This is probably why the government is moving towards gradual deconfinement: so that the measures are lifted while keeping the epidemic under control.

What we do know is that today in France, we are in an extremely different situation from the British deconfinement, where we had around 2,000 cases per day, almost more deaths and around half of the population. vaccinated population.

We are not there at all.

So either the French deconfinement, in its modalities, will not be comparable to that of the United Kingdom.

Either there is a risk of the epidemic taking off again.

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Coronavirus: Jean Castex ensures that the variants "tend to regress" in France

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