How far can you rely on vaccines to contain the Covid-19 epidemic? Even if their effectiveness decreases against contaminations, doctors point out that their role remains essential. But, in the long term, a question arises: the place to be left for natural immunity. “We now know that vaccination will not eradicate SARS-CoV-2”, the coronavirus causing Covid-19, acknowledged Wednesday, in a statement, the Academy of Medicine, the body supposed to carry the discourse of discipline in France.

For several weeks, data have been accumulating to demonstrate a lower efficacy of vaccines against the Delta variant of SARS-CoV-2, which is clearly more contagious. Vaccinees have, in a not insignificant proportion, been infected by the virus, even if they remain very well protected against the serious forms. It therefore becomes difficult to envisage collective immunity, that is to say a sufficient threshold of immunized people for the epidemic to stop progressing. However, the Academy of Medicine calls for “not to renounce” this collective immunity. Because a nuance of size is often misunderstood.

Collective immunity is not the same as making the virus completely disappear. The objective is that the number of contaminations remains stable over time or, at least, only experiences regular fluctuations over the seasons. And it is the vaccination of the greatest number that makes it possible to accelerate this evolution “towards a profile of banal infection with seasonal recrudescence”, according to the Academy.

For this, the initial role of vaccines is hardly any debate within the scientific community. But beyond that, it is less obvious to settle the question of the strategy for the years to come. Should we bet everything on vaccines and increase the number of booster shots to compensate for their loss of effectiveness? “The objective is not to continue having to vaccinate for eternity”, qualified the German virologist Christian Drosten at the beginning of September, on the NDR channel.

According to him, no doubt, we must currently vaccinate as many people as possible, in order to prevent a first encounter with the virus resulting in a serious form of the disease. But later, infections can be allowed to occur in large numbers among the population, at least when people are not at risk.

In individuals who have already been vaccinated, these contaminations will have little risk of being dangerous, according to the virologist, who thus relies on a global immunity built by successive bricks (vaccine and natural infection).

Mr Drosten, who expresses a personal position, is based on a crucial notion, that an infection with the virus allows one to be immunized longer and more effectively than if one has been vaccinated.

At the end of August, a retrospective study carried out on several hundred thousand people in Israel – a country particularly in advance of vaccination – concluded that contaminations were much more frequent in people vaccinated than in those who had already been infected with the virus.

These data – to be taken with caution because not yet independently evaluated – should not, however, suggest that it is better to let yourself be infected instead of being vaccinated. Some researchers, anxious to avoid interpretations unfavorable to vaccination, therefore emphasize that we are still far from being able to develop a strategy that leaves room for natural immunity. “It is a situation which could happen but which is not yet for now”, nuance with AFP Jean-Claude Manuguerra, virologist at the Pasteur Institute. “We still have a lot of people around the world who are not vaccinated.” He does not however reject the merits of this strategy, provided that care is taken to continue to target people most at risk. .

Another element to watch for Mr. Manuguerra: the circulation of the coronavirus in children who, too young to have been vaccinated, can constitute a “big playground for the virus” even if they have only a tiny risk of themselves develop severe forms.

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