Public health experts determined that face masks are a key tool in reducing the spread of the new coronavirus, but not all masks are equally effective and some can even be counterproductive.
A new study classified 14 types of commonly available face masks and found that medical masks offer significantly greater protection against the spread of virus droplets than cotton masks, while neckerchiefs are of almost no use.
The findings published in the American journal Science Advances They have public policy implications, particularly in countries like the United States, where authorities encouraged the population to wear cloth masks and leave medical-type masks to health workers because they are scarce.
“We need to increase the production and distribution of surgical masks”, tweeted Tom Frieden, former director of the Centers for Disease Control and Prevention during the president’s administration Barack Obama, after the publication of the study.
Face masks are important because 30% to 40% of infected people may show no symptoms, but they still unknowingly transmit the virus by coughing, sneezing, or just talking.
We need to scale up surgical mask production and distribution. https://t.co/c8TGG3c5qM
– Dr. Tom Frieden (@DrTomFrieden) August 9, 2020
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For this study released on August 7, researchers at Duke University in the United States had several masked participants speak in a dark room in the direction of a laser beam, while the scene was recorded (people repeated: “Stay healthy people” and “Take care”).
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Unsurprisingly, N95 masks reserved for hospital personnel (the American standard equivalent to European FFP2) are the most effective, reducing droplet transmission by more than 99.9%, compared to not wearing a face mask.
Surgical or polypropylene masks were not far behind, reducing droplet transmission by 90% or more compared to those without a chinstrap.
The cotton face masks provided good protection, eliminating 70% to 90% of normal speech aerosols, depending on the number of layers and folds.
Surgical masks, effective to stop COVID-19; neckerchiefs NO, says study
But the scarves only reduced scattered droplets by about 50%.
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The worst of the 14 masks tested was the neckerchief, the kind runners wear: this fabric actually increased the number of droplets expelled, possibly because the material helped disperse the larger droplets into many smaller ones.
Finally, the N-95 round valve masks, designed for industrial settings where exhalation by the user is less important than inhalation, performed roughly on par with cotton masks in terms of the number of droplets transmitted.
Health authorities have discouraged the use of N-95 masks with valves because, while they protect the wearer, they more easily spread contaminated air exhaled by a person.
The study co-author, Eric Westman, said this information had already served to prevent the mass purchase of a type of mask that he and a local nonprofit had planned to distribute for free in Durham, North Carolina, where the university is based.
“The notion that ‘anything is better than nothing’ proved not to be true”, said.