Washington (AFP)
As new, more contagious variants of the coronavirus spread, it becomes necessary to wear better quality masks, meeting stricter standards, or failing that, a surgical mask overlaid on a fabric mask, according to many experts.
Scientists now agree that the virus is mainly released into the air, rather than through contaminated surfaces.
And there is growing evidence that very fine droplets, which can be projected up to several feet away when someone speaks or breathes - much like cigarette smoke - can be enough to transmit the disease.
To make matters worse, some variants, such as the British, are now transmitted more easily than the virus that circulated until now, according to the opinion of many experts.
But these solutions are far from ideal.
So how can we do better?
- Filtering mask and ... adjusted -
"The effectiveness of a mask depends on two things: filtration, and its fit," Linsey Marr, a professor at Virginia Tech University who has studied airborne diseases, told AFP.
"Good filtration prevents as many particles as possible from passing through, and a good fit means that there are no leaks around the edges of your mask, through which air, and therefore virus, can pass", she adds.
Even a small space can lead to efficiency reduced by 50%, she said.
The best materials for blocking very fine particles include non-woven polypropylene, used in many surgical masks or more filtering masks like KN95.
When it comes to fabrics, very tight cotton works best, according to Linsey Marr.
“You should feel your mask being sucked in as you breathe in, and if you put your hands to the sides, you shouldn't feel any air coming out as you breathe out,” says the scientist.
Masks with a metal shaft allow a better fit of the nose, and they fit better when the rubber bands wrap around the head, not just the ears.
- Two masks are better than one -
"If you wear a fabric mask, choose one that has multiple layers, ideally with a small pocket that allows a good filter to slip inside," recommends the researcher.
"Or you can double it up, wearing a surgical mask under a cloth mask."
Surgical masks are made of a material that filters well, but they tend to be quite loose.
Adding a fabric mask can therefore help keep its edges against the face, reducing leakage.
Adding a layer also improves filtration - if one layer retains 50% of the particles, adding a second will achieve 75%.
But "we don't recommend wearing more than two masks" on top of each other, she adds.
"This can compromise the ability to breathe well. However, it must remain easy to breathe, otherwise the air will have a better chance of escaping through the holes in the sides of the mask."
- Medical grade masks -
Another option: KN95 or FFP2 masks depending on the country, often reserved for caregivers.
These are the most filtering masks.
"They all provide a similar level of filtration, for particles entering and exiting," says Ranu Dhillon, a physician at Brigham and Women's Hospital and Harvard Medical School.
He has been campaigning for better masks since the spring, and regrets the lack of information given to the public on their benefits.
"There was no concerted effort to really produce and distribute them en masse," he laments.
- Masks forever?
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Even after the coronavirus crisis has passed, the masks may well partially remain.
Before the pandemic, Donald Milton, a professor at the University of Maryland, along with other scientists, studied the flu and concluded that it could also be transmitted via the fine particles released by speaking or breathing.
The role of sneezing, coughing and surface transmissions is less than initially estimated, they say.
At the time, their research had sparked controversy, but it was revived by the Covid-19.
Wearing a mask may therefore continue to be encouraged in the future during the flu season.
© 2021 AFP