By HAJIME MIKAMI/ Staff Writer
October 29, 2020 at 07:10 JST
A new study says wearing a face mask is effective at preventing airborne transmission of the novel coronavirus, particularly so when a person infected with the deadly virus puts on one.
A group of researchers from the Institute of Medical Science at the University of Tokyo conducted experiments where they gave mannequins mock artificial respiratory systems and had them wear different types of masks.
A special chamber was developed to simulate airborne transmission of the actual novel coronavirus and measure the amount of infectious droplets, which are produced by humans breathing and coughing, that pass through the mask a mannequin is wearing.
The study, published Oct. 21 in the online version of the U.S. science journal mSphere, was led by Yoshihiro Kawaoka, a virology professor, and Hiroshi Ueki, a project assistant professor, both at the institute.
The study is significant because amid the pandemic, especially at its earliest stages, there was a lack of consensus and evidence on whether masks are effective for protecting against airborne transmission of the virus.
In the paper, researchers said, “We found that cotton masks, surgical masks, and N95 masks all have a protective effect with respect to the transmission of infective droplets and aerosols” of the novel coronavirus, and that “the protective efficiency was higher when masks were worn by a virus spreader.”
In the experiment, researchers placed two mannequin heads near one another facing each other. One was labeled as a COVID-19 patient and was set up to emit a mist through its mouth, mimicking a virus spreader exhaling.
The other, a “non-patient” and otherwise healthy mannequin, was connected to an artificial ventilator and equipment that let researchers detect how much of the virus it would inhale.
A gelatin film was placed along the respiratory tract, and the amount of virus attached to it was measured.
The researchers tested a range of scenarios with three types of face masks placed on the mannequins: an N95 mask, a surgical mask and a cotton cloth mask.
When the infected mannequin wore a surgical or cotton mask, and the healthy mannequin did not wear a mask, it reduced the amount of the virus that the healthy mannequin inhaled to 20 to 40 percent of the amount that the healthy mannequin inhaled with no mask.
When the infected mannequin wore an N95 mask, a type of mask that is not expected to be worn by a COVID-19 patient, the amount of the virus that the healthy mannequin inhaled was nearly zero percent.
When the infected mannequin did not wear a mask and the healthy mannequin wore a surgical mask, it reduced the amount of the virus that the healthy mannequin inhaled to 50 percent of the amount of virus it inhaled with no mask.
The amount was reduced to 60 to 80 percent with a cotton mask, while it was reduced to 10 to 20 percent with an N95 mask.
When both mannequins wore a cotton mask, the amount of inhaled virus dropped to 30 percent of the amount inhaled when neither wore masks. When they both donned a surgical mask, the figure dropped further, to the range of 20 to 30 percent.
But an N95 mask needs to fit the wearer’s face perfectly to work most effectively. When the mannequins did not wear N95 masks correctly, they had about the same result as they would wearing a surgical mask.
In each instance, including when they both wore masks, the researchers found genes of the virus made their way into the respiratory tract of the healthy mannequin. But they said more research is needed to determine whether those genes would necessarily cause infection.
“It is important for everybody to wear a mask to prevent the spread of the pandemic,” said Kawaoka.
But he also cautioned the public “not to put too much trust in masks,” and advised that they take other preventative measures, such as keeping a safe distance from each other as well.
The paper can be read here: (https://doi.org/10.1128/MSPHERE.00637-20)
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