Mask mandatory: is the glass half-empty or half-full?

Masque obligatoire: le verre est-il à moitié vide ou à moitié plein?

Masque obligatoire: le verre est-il à moitié vide ou à moitié plein?

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14 July 2020 14: 20

Updated at 15h19

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Mask mandatory: is the glass half-empty or half-full?

Masque obligatoire: le verre est-il à moitié vide ou à moitié plein?

Masque obligatoire: le verre est-il à moitié vide ou à moitié plein?

Jean-François Cliche

The Sun

BLOG / Next timing, the physicist of the University of Montreal Normand Mousseau could hardly have hoped for better — or worse, depending on your point of view. His open letter in which he denounces the obligation to wear a mask in enclosed public places of Montreal (“Mask mandatory, science-optional”) was published in The Press, just 48 hours before the government announced that the same measure will apply to all of Quebec, from Saturday next.

Essentially, it criticizes the scientific basis on which the directors Plant has supported his decision, bases which seem to be clearly inadequate to impose the mask at all : “the scientific evidence demonstrating the usefulness of wearing a mask generalized to prevent the spread of a virus are very low, particularly in a context where this virus is not very widespread (we’re talking about, in Quebec, for example, of less than 100 new cases per day, for a population of over 8 million people) and that measures of distancing physics are in place,” he wrote.

In a debate like the one on the port of the mask where a lot of people are very on edge, either because they fear the COVID-19, like the plague, either because they don’t care, or even dispute his existence, and categorically refuse the wearing of the mask, the letter from Mr. Mousseau has caused the turmoil that could be expected. Some readers have also helped me asked what I thought of it. So, as we’ll all have to wear masks in a few days, see what it is.

First, is it true that the scientific evidence of the effectiveness of the port widespread of the mask are at this point “weak” ? We can easily find studies that find in favor of the port of the mask, it must be said — the Fédération des médecins spécialistes du Québec pointed out on Twitter in a reply to Mr. Mousseau. For example, there are studies of physics like this on the dispersion of droplets in the air, with and without a mask. And if the COVID-19 is spread in infected droplets that are projected into the air by coughing, sneezing or even just speaking, it is entirely logical to think that a mask that prevents their dispersion will slow significantly the spread of the disease.

However, between “logical implication” and “proven”, there is a good margin of science, and it is not always easy to overcome. In a review of the scientific literature published last month in The Lancet, researchers have found a whole series of work suggesting that, yes, there is reason to think that the wearing of the mask seems to indeed prevent the spread of the COVID-19. But for all sorts of reasons, they indicate that the level of certainty to this conclusion is “down” :

Masque obligatoire: le verre est-il à moitié vide ou à moitié plein?

Chu et al, The Lancet, 2020

Most of the studies taken into account by The Lancet were not the COVID-19 itself, but on two other coronavirus recently emerged, is the severe acute respiratory syndrome (SARS), and respiratory syndrome Middle East (MERS). It is not sure at all that these two are actually like the COVID-19. In addition, the vast majority of this work had measured the prevention of hospital infections, and not in the community. Because of this, it is the effectiveness of masks and specialized and extremely powerful, such as the N95 or surgical masks, which has been examined, and not that of masks fabrics, or other materials that are much less effective in which are made the cover-face of Mr. and Mrs. All-the-World. The conclusions drawn in specific contexts can they be generalized ? This is not self-evident, where the little coverage that the authors of The Lancet show towards their results.

There are also a number of more recent studies like this one published in Health Affairs, which is a measure of the spread in places that made wearing a mask mandatory in other jurisdictions where it is optional. But this is not particularly robust because they compare the entire populations is very far from ideal (it is necessary to stretch the more possible the individual data), and the legal obligation of wearing a mask does not inform, necessarily, on compliance and enforcement.

All that to say that we did not really have the choice to give reason to Mr. Mousseau about this specific point (I’ll be back on the rest) : evidence that the port’s generalized mask, and not just the N95 in the clinic, which slows down the progress of the COVID-19 are actually thin. In this respect, moreover, this series of comments of epidemiologists and experts in published last weekend on the website of the Science Media Centre in the uk is quite telling. Asked to comment on a statement by the prime minister, Boris Johnson, who said to consider how to make the mask mandatory in all closed public spaces, all pointed to a “lack of evidence of effectiveness in the real world”, of “mixed results” and a level of evidence “extremely weak”.

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Then once we know this, what is it made of ? You can borrow the same way that Mr. Mousseau, and conclude that if the evidence of efficacy is lacking at this point, so we can’t justify the obligation to wear the mask. It is a position that defends itself quite well, from a logical point of view.

But there is another possibility, one that many epidemiologists prefer. Without having evidence within the meaning (in the least) strong, was still reasonable grounds to believe that it works, or at least that the mask, even simple fabric, makes a difference. Not as strong as the medical masks, it is true, but it is reasonable to think that it helps. And as there was no kind of consequence to put on a mask from time to time, apart from a minor inconvenience, then it is just as reasonable to want to at least promote, and even require wearing a mask in certain circumstances. All the more that, for the moment, we don’t have many other alternatives.

It is not bad what Dr Ben Killingley, hospitals of the University College of London, told the Science Media Centre : “This pandemic has posed challenges that we were so far unknown. Our plans and our stock [of medical masks] were designed to deal with an influenza pandemic, but the pandemic of SARS-CoV2 [the virus that causes the COVID-19] is presented with a transmission rate higher, no antiviral treatment and no indication that we will have a vaccine soon. It therefore represents a problem very different, and the bar, so to speak, has been lowered : everything that could help should now be considered if the disadvantages can be minimised.”

It is essentially the same spirit that we find in this letter published in may in the medical journal Annals of Internal Medicine : no, of course, the covers-face-simple tissue does not filter as effectively as the medical masks, far from it, but “the point is not [just] not that a number of particles pass through, lobbied for the authors. It is rather that a number are stopped, especially at the end. Any particle of infected which is retained in a mask is a particle that will not remain suspended in the air in aerosol form, or which will not land not on a surface and then they find themselves on a hand”. Even if it is only between 10 and 40 % of the aerosol remaining in the mask, as studies have shown, for certain tissues, it is always it will be taken.

I think it is in this sense that one must understand the fact that most of the public health authorities of the world recommend is now wearing a mask, including the world health Organization, the CDC in the United States, Health Canada, and so on. The evidence of effectiveness are far from being concrete, it is true, but we know that it can’t hurt, and there is reason to believe that this helps to a certain extent, so let’s go with-y.

For what it is worth : personally, I finished by letting me convince him. It took me a certain time (mea culpa) because I feared the discomfort, and not without reason, but to force them to see these studies and expert opinion, to wear the mask (in enclosed public places) has come to seem the most rational to do.

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