Covid-19: a Danish study asks about the mask, without providing an answer

A Danish study published on Wednesday suggests that wearing a surgical mask has only a small effect in protecting against COVID-19, but many scientists point to its limits and stress that it does not lead to a conclusion solid.

One of the authors, Kasper Iversen (University of Copenhagen), himself told AFP that “the current recommendations (to wear a mask when distancing is impossible, note) are not seriously questioned by the study ”.

Covering 6,000 people, the study, published in the Annals of Internal Medicine of the American College of Physicians, shows that 1.8% of mask wearers contracted COVID-19, compared with 2.1% of those who was not wearing it.

While this suggests that the mask has a small protective effect, the sample size is still insufficient to establish statistical significance, according to its authors.

“We were not able to show a significant effect”, explained Professor Iversen, for whom the effect of wearing the mask, if not insignificant, “is not as important as we expected. “.

However, a companion article published with the study points to its important limitations.

On the one hand, it was carried out in a country with relatively low transmission rates. Then, less than half of the participants (46%) correctly applied the instructions for wearing the mask. Finally, its results are based on antibody detection tests, the reliability of which is variable.

“The specificities of the framework of the study limit not only its statistical strength but also the generalization of its conclusions”, according to this comment annexed to the study.

“There is absolutely no doubt that the masks work to prevent infecting others, and possibly to protect those who wear them as well,” commented author Tom Frieden on Twitter.

This is another limitation: the study focuses only on the degree of protection mask wearers can expect when no one else is masked. However, the mask is recommended above all to prevent its wearer from contaminating others.

The study, dubbed ‘Danmask-19’, was conducted in Denmark between April and May, at a time when almost no one in the country wore masks except for infectious disease departments in hospitals.

Half of the cohort of people followed was asked to wear a mask outside their home and the other half not to wear one.

All had to follow the recommendations in force and other barrier gestures. Bars and restaurants were closed at the time.

In Denmark, relatively spared by the pandemic, wearing a mask has gradually become mandatory since August with its introduction in public transpors, then came the turn of bars, cafes and restaurants and finally that at the end of October of all closed public places. .

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