By settling in the territory, the Delta variant almost caught everyone by surprise. More than 20 new cases of Covid – 07 per day on average in mainland France, and a curve of hospital deaths which begins a dark ascent. Far from a serene summer sheltered from the virus, this “fourth wave” already well established is competing with a vaccination campaign carried out by the government to save what remains of the summer holidays, and minimize the impact on the start of the school year. The extension of the health pass from August 9 should help, coupled with a strategy of “going to” aimed at providing the vaccine especially to the most vulnerable and isolated categories. Objective, 50 million first-time vaccinated at the end of August .

But will that be enough to counter the increase in contamination, and hope for an end to the crisis? “It would be a utopia to believe that only vaccination would pull us out of this pandemic, at least for the months to come,” emphasizes Antoine Flahault epidemiologist and director of the Institute for Global Health at the University of Geneva. In France, a little more than half of the population has currently received a complete vaccination, a level still largely insufficient to hope to contain contamination and above all to avoid strong pressure on the hospital .

But in recent weeks, various publications have brought to the fore another essential question in the face of the Delta variant: how effective are vaccines in countering infections and transmission? ? In a document released on Friday the American Centers for Disease Control (CDC), estimated that this strain, first identified in India, had been a game-changer in the fight against Covid. Much more contagious than the previous ones, it would be according to this document as transmissible as chickenpox and would, above all, lower the effectiveness of vaccines. “The war has changed,” summed up health officials.

Return of the mask in closed places? Faced with these findings, scientists are cautious and urge us to put things into perspective. “The American CDCs discover a little late that vaccines do not block transmission, which we have known for a long time, but they prevent almost all serious forms of Covid – 20 and c ‘is extraordinary progress, “notes Antoine Flahault. Same observation on the side of Eric Billy, researcher in immuno-oncology and member of the Du Côté de la Science collective: “The CDC data only confirm what was said from the start, namely that vaccination essentially protects against forms symptomatic and asymptomatic but could not prevent transmission to % because the immunity generated is not mainly mucosal (on the mucous membranes of the nose in particular) “.

Still, the contagiousness of the vaccine has somewhat changed the rules of the game. “The Delta has changed the effectiveness of vaccines by reducing protection against asymptomatic forms “, summarizes Eric Billy. New data to be taken into account in controlling the epidemic and which prompts the American health authorities to review their recommendations on the mask. In recent days, the latter have estimated that it is now necessary even for people vaccinated in closed places.

With the likelihood of a virus circulating in a population where vaccination is not sufficient, additional epidemic control measures should review the day. “We must combine effective measures with each other, tireless and perhaps compulsory vaccination, but also barrier measures and social distancing, such as teleworking, or the extensive use of the health pass which could prove to be a valuable aid. in the fight against the pandemic “, suggests Antoine Flahault. This message joins that of the WHO which called at the end of last week to “act”, in the face of the Delta variant. “The same measures that we applied before will stop this virus. They stop the Delta variant especially if you add vaccination”, argued Friday Mike Ryan, in charge of emergency situations at the World Health Organization.

“Belt and suspenders” The importance of these measures, sometimes qualified as “non-pharmaceutical”, is also found in the need to avoid the appearance of new, potentially more dangerous variants. A recent article published on the journal’s website Nature , assessing the impact of virus transmission rates and vaccination on the emergence of resistant strains to vaccines, unsurprisingly asserted that a “rapid vaccination rate decreases the likelihood of emergence of a resistant strain”. But the authors noted that “counterintuitively, when a relaxation of non-pharmaceutical interventions occurred at a time when most individuals in the population had already been vaccinated, the likelihood of emergence of a resistant strain was considerably. increased “. “Therefore, we show that a period of transmission reduction near the end of the vaccination campaign can significantly reduce the likelihood of new resistant strains emerging,” they concluded.

“At this time, we should have a belt and suspenders to try to fight this epidemic”

What make politicians think. Particularly in France where certain restrictions on wearing masks indoors could be lifted when the presence of a health pass is mandatory. “A bad idea”, judged the epidemiologist and member of the Scientific Council Dominique Costagliola. “At the present time, it would be necessary to have a belt and sling to try to fight this epidemic and not remove certain measures to put in place others”, she lamented to France Inter . “There are not fifty solutions, we must limit the spread of the virus and therefore limit the number of new cases and we must especially vaccinate the population as much as possible, the two approaches are complementary and one does not replace the other “, insists Eric Billy.