While the public authorities are stepping up their vaccination campaigns around the world to come to terms with the Covid-19 pandemic, the appearance of mutations in the virus considered to be more resistant to the vaccine continues to cause concern. If the Delta variant, spotted in India, is today the majority in France and around the world, the World Health Organization has recently identified several new mutations called Mu, Lambda or Epsilon which would also present a said risk. of "immune escape", partially neutralizing the antibodies present due to vaccination or a past infection. To better understand this notion, which has become crucial in the fight against Covid-19, France 24 spoke with Professor Jean-Daniel Lelièvre, head of the department ofimmunology and infectious diseases at the Henri-Mondor hospital in Créteil.

France 24: Can you explain to what corresponds the risk of immune escape raised by the WHO with regard to certain variants?

Jean-Daniel Lelièvre:

The immune escape refers to the less effective protection of people who have been vaccinated, or who have already been sick, in the face of certain viral strains responsible for Covid-19.

These people have developed antibodies that give them immunity for several months, which will wane over time.

But the Covid-19 has the particularity of mutating quickly and a lot.

The more the new version of the virus is different from the original, the weaker the pre-existing immunity.

However, although the vast majority of variants do not pose any particular problems, modifications are observed in some of them which are in a way flaws and can make the antibodies less effective.

Does this immune escape threaten the effectiveness of vaccination coverage today?

There are two major problems with variants today, immune escape, which therefore makes immune people more vulnerable, and the greater contagiousness observed with certain variants, such as Alpha and Beta variants. With the spread of Covid-19 across the world, the variants that become the majority tend to combine these two characteristics. Today, people vaccinated with the initial form remain protected from severe forms of Covid-19, even in the face of new variants. But the question is, for how long ...

So far, we have not detected mutations different enough in the strain to significantly lower the efficacy of the vaccine because the antibodies are not unique and target several important parts of the virus.

But we cannot completely exclude this risk because it must be admitted that we were surprised by the rapid appearance of the Sars-CoV-2 variants and that we still do not fully understand the mechanisms of selection of the mutations of the virus.

What health measures can best combat this risk of immune escape?

The risk of immune escape is one of the reasons for opening vaccination to as many people as possible: the more we prevent the spread of Covid-19 among the population, the more we reduce its mutation capacities. It is also during periods of lifting of restrictions that we have observed significant mutations in Covid-19 - and in particular the appearance of the Delta variant. We must therefore block the chains of transmission with barrier gestures, of course, but also and above all by massively vaccinating. The difficulty today is that we are in a race against time but we lack data. With sequencing, we spot these modifications, sometimes in parts critical for the immune response, but then we have to analyze the evolution of the variant because it is only s'it takes precedence over the other forms that it should receive special attention. It is therefore necessary to adapt the vaccination policy according to the evolution of the risk. Faced with these new variants, which present disturbing mutations, it now seems necessary to move towards the generalization of the third dose to the entire population in order to maintain a sufficient level of vaccine efficacy.

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