Science

Last stage of deconfinement: what if France neglected aerosol contamination?

The importance of opening everything up at the time of deconfinement. While France has taken a new step towards normal life with the reopening on Wednesday of indoor bars and restaurants, many specialists stress the importance of ventilation in the fight against Covid-19. According to them, this mode of contamination has too often been underestimated by the French authorities.

“Without speaking of denial, the route of contamination of Sars-CoV-2 by aerosols has been too neglected since the start of the pandemic”, underlines to L’Express the epidemiologist Antoine Flahault, director of the Institute of Global Health from the University of Geneva. Are the current measures sufficient to support the reopening?

Slow evolution

For a long time, the main modes of transmission of the coronavirus identified were droplets, as well as contaminated surfaces – hence the recommendations to wash your hands frequently with soap or hydroalcoholic gel, or not to shake hands. Scientists then alerted to another mode of transmission: aerosols, that is to say particles suspended in the air.

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In July 2020, the World Health Organization (WHO) finally acknowledged that “new evidence confirms the potential for airborne transmission of the new coronavirus, a crucial aspect to be taken into account in any mechanism for reopening public places”.

“Aerosol contamination practically only occurs in closed, poorly ventilated areas, in which there are people and where we spend several tens of minutes at least,” explains Antoine Flahault. However, the risk has often been forgotten despite the evidence put forward by specialists. Last October, President Emmanuel Macron finally stressed the importance of airing his home, a simple gesture (and a sometimes mocked instruction), but that some could forget to do.

“Incomprehensible blind spot”

Instructions were scarce. “Not a word, and for good reason, on this incomprehensible blind spot: aerosolization has never been seriously taken into account, neither in public health messages, nor in fact, for more than a year”, denounced at the beginning of June in Release writer and physician Christian Lehmann.

“It took fourteen months for, little by little, at the international level, aerosolization to finally be considered as a major route of contamination, far superior to manual contamination.” On this question, Christian Lehmann criticizes the epidemiologist Didier Pittet, author of a report on the management of the crisis submitted to Emmanuel Macron in mid-May.

“Throughout the crisis, he fiercely fought the hypothesis of aerosol contamination,” says Christian Lehmann. Didier Pittet, invited on France Inter on May 18, declared in particular: “There is no scientific data on [le pourcentage de contamination par] aerosols (…) This question will remain open ”

On this question, the man has “a position against the scientific consensus”, according to The world. “It turns out that today we agree that this is the predominant route of transmission, if not the exclusive route, and this has major implications in terms of prevention measures which were most often delayed or were notoriously insufficient, “explains Antoine Flahault to L’Express.

Sufficient protocols?

The government published on May 12 the health protocol for businesses which began to reopen on May 19. Regarding the ventilation of stores, businesses undertake to “ventilate the premises by natural or mechanical ventilation in working order. When possible, favor ventilation of the room through two distinct points”. Another instruction: “promote the measurement of carbon dioxide in the air. The measurement of CO2 in the air must be carried out at significant places of frequentation and at periods of real busy frequentation”, we can read.

In detail, “above 1000 ppm, the room must be evacuated for sufficient ventilation time to find CO2 levels below 800 ppm. CO2 in the air must be measured at significant places of frequentation and at periods of real busy frequentation “. With these figures, “we are still far from a risk control protocol,” Bruno Andreotti, professor at the University of Paris and researcher at the Ecole normale supérieure, told AFP. Setting a threshold as high as 1000 ppm “is not serious”, he said.

Concerns are even greater after reopening indoors, because the risk of contamination is much higher, especially in insufficiently ventilated spaces. Are the measures sufficient? “In a sense, since it is not possible to make the atmosphere of an enclosed space as well ventilated as the atmosphere outside, one can say that no measure is ever ‘enough’. Because none of these measures do not reduce the risk of indoor contamination to zero, “said Antoine Flahault.

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The epidemiologist cites the following measures to reduce the risk of transmission: “the (correct) wearing of a mask, half gauges, physical distance between people, short exposure time and adequate ventilation.” Moreover, according to him, “when the virus circulates little in the community, as is the case in June throughout Europe, or when all those present are vaccinated or are cured of a documented Covid, then the risks contamination are considerably reduced even if the measures are not all applied “.


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