Paris (AFP)

Reducing barrier gestures such as wearing a mask and physical distancing at a time when the entire population has not yet been vaccinated significantly increases the risk of the appearance of vaccine-resistant variants of the coronavirus, shows a study published on Friday.

While nearly 60% of Europeans have received at least one dose of the Covid-19 vaccine, this study shows the need to maintain precautions other than the vaccine until everyone is immunized, explain its authors .

To study how the coronavirus could mutate in response to increasing vaccine coverage, a team of researchers from several European countries simulated the likelihood that a vaccine-resistant strain would emerge in a population of 10 million people. 'here at three years.

Their model integrates as variables the level of the vaccinated population, the virus mutation rate and its speed of transmission, anticipating successive "waves" with a surge in contamination followed by a drop in new cases after the introduction of restrictions (confinements , etc.).

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Not surprisingly, the study, published in the journal Nature Scientific Reports, concludes that rapid vaccination reduces the risk of emergence of a resistant strain.

But, more counter-intuitive, their model also shows that this risk is maximum when a large part of the population is vaccinated, but not enough to ensure group immunity.

This phenomenon is termed "selection pressure": as more of the population has developed antibodies against the virus, the competitive advantage of more resistant strains increases.

According to the researchers, it is from a threshold of 60% of vaccinated that the probability of emergence of resistant variants becomes high.

This corresponds to the current situation in most European countries, facing the rapid spread of the Delta variant.

Globally, just over a billion people are fully immunized and some countries, especially in Africa and South America, have yet to start large-scale immunization due to a lack of doses.

These results show the need to maintain precautionary measures until everyone is vaccinated and to make "a truly global vaccination effort", otherwise "vaccine resistant strains could be eliminated in some populations but persist elsewhere. ", before spreading, underline the authors.

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