أخبار عاجلة

Canada's mask guidance has changed. Here's why you might need an upgrade

اخبارالعرب 24-كندا:الخميس 25 نوفمبر 2021 04:28 صباحاً Now that the cold weather has hit and people are moving inside, many doctors and scientists are urging Canadians not only to resist getting complacent about wearing masks to protect against COVID-19 — but also to take a closer look at whether that cloth mask is keeping you and others as safe as possible.

"In general, while non-medical masks can help prevent the spread of COVID-19, medical masks and respirators provide better protection," the Public Health Agency of Canada (PHAC) said on its COVID-19 mask information webpage, which was updated on Nov. 12.

The updated guidance also recommends medical masks or respirators for people "who are at risk of more severe disease or outcomes from COVID-19" and those "at higher risk of exposure to COVID-19 because of their living situation."

Respirators — such as N-95 and KN-95 masks — are considered the highest level of mask protection and were previously recommended only for health-care workers coming into direct contact with infectious patients. In those high-risk areas, respirators require a "fit test."

But in a nod to more general use, PHAC's guidance now says: "A respirator worn in the community doesn't need to have been formally fit tested, as is required in some occupational settings."

Responding to a CBC News inquiry about why PHAC's recommendations have changed, the agency said in an email it was "based on the latest scientific evidence on SARS-CoV-2 virus variants of concern, increased understanding of the impacts of vaccination and immunity in the population, and new data available on mask types and their effectiveness."

In addition to the updated online guidance, Dr. Theresa Tam, Canada's chief public health officer, recently posted a series of tweets illustrating how COVID-19 could spread through the air, using the analogy of second-hand smoke. 

Many doctors, scientists and engineers say this shift in messaging reflects a growing body of evidence suggesting that COVID-19 is largely spread through aerosols (tiny particles that can hang in the air), and not just through respiratory droplets (larger particles) transmitted by close contact with an infected person. 

In turn, that means it's important to re-evaluate the masks we're using, they say.

"This marks a transition in Canada toward a recognition of how important aerosol, airborne-based transmission is in transmission of this virus," said Dr. Brooks Fallis, a critical care physician at the Toronto-area William Osler Health System.

Because aerosol particles are smaller and can accumulate in the air over time, Fallis said, the best-performing masks are critical if you're going to be indoors with other people for a while.  

Some doctors recommend wearing a respirator, like this N-95 mask, if you're in a closed indoor space with other people for a significant period of time. (Adrian Wyld/The Canadian Press)

"If you're just, you know, popping into the grocery store to grab a couple of items, or you're … walking along a crowded street and you want to wear a mask, then it's fine [to wear a medical mask]," Fallis said.  

"But if you're in a closed space with lots of people, then we should be upgrading to higher-level masks, like the KN-95 masks or a respirator-type mask, which provides better fit and better filtration."

Masks are important even when you're fully vaccinated, both PHAC and doctors say, because although it's much less likely, infection with the virus that causes COVID-19 — especially the highly transmissible delta variant — can still happen.

Better availability of higher-grade masks

Another important factor that's changed since the beginning of the pandemic, experts say, is the availability of medical/surgical masks and respirators. 

"There was a lot of controversy about N-95 masks because there weren't enough for the health-care workers. So the message then, quite understandably, was: 'Save those for the health-care workers and we will use other alternatives,'" said Marianne Levitsky, an industrial hygienist with the Dalla Lana School of Public Health at the University of Toronto. 

"But things have changed a lot. We now have Canadian manufacturers making N-95-type masks and they're much more widely available than they used to be," she said.

WATCH | Respirators are considered the highest level of mask protection: 

Should N-95s become the new mask standard?

6 hours ago
With increased concern about the aerosol spread of COVID-19, new guidance suggests N-95s should be worn in high-risk situations, but experts say cloth masks still have their place and new manufacturing standards are improving the quality. 1:59

Why your masks may not be as protective as you think

8 months ago
With more contagious variants of COVID-19 on the rise, there’s more talk of improving people’s masks. The type of mask is important, but as The National’s Andrew Chang found out, so is its fit. 4:47

Experts agree any mask is better than no mask, because it will catch droplets and aerosols coming from the wearer's nose and mouth and protect others. But there's growing evidence that a higher-quality mask can also provide some protection for the wearer.

"The masks or respirators, they control in two ways. One, they can prevent an infected person from emitting those infectious aerosols into a space, and they can also protect the person who is wearing them from inhaling them," said Levitsky.

Conor Ruzycki, who studies aerosol science and technology at the University of Alberta, says respirators, like the Canadian-made one he's wearing, provide better protection against aerosol transmission of COVID-19. (CBC)

"Cloth masks were always sort of something that was going to buy us some time as we move toward something better," said Conor Ruzycki, a PhD candidate in mechanical engineering at the University of Alberta who studies aerosol science and technology.

"Now that we understand this disease better, we know that these small aerosols are playing a bigger role; we should be moving toward … using better mask materials."

The 3 Fs of choosing a mask

There are three F-words to keep in mind when assessing how well a mask will protect you and others: Fit, filtration and function (also called breathability). 

"Fit is essential in terms of how effective filtration happens in a real setting," said Ravi Selvaganapathy, a professor of biomedical engineering at the Centre of Excellence in Protective Equipment and Materials at McMaster University. 

"You can have the best quality material out there, but if it doesn't fit one's face, then most of the air goes through these large gaps that exist and not through the filter material."

The filter material in both medical/surgical masks and N-95 respirators is actually the same — but respirators contour better to a person's face, said Selvaganapathy.

A "knot and tuck" adjustment can improve the fit of disposable masks — including medical masks, the Centers for Disease Control and Prevention (CDC) advises.

"Knot the earloops of a three-ply face mask where they join the edge of the mask," the CDC website says. "[Then] fold and tuck the unneeded material under the edges." 

Cloth masks often offer good fit and good function (breathability), but how well they filter out virus particles is usually a wild card, experts say, because they're made of varying materials and aren't regulated.  

"There are no standards. When you buy a cloth mask, it does not usually tell you what the filtration is," Levitsky said. They can protect anywhere from 20 per cent to 80 per cent, she said. "So it's a big unknown." 

Filtration for medical/surgical masks and respirators is graded by the standards organization ASTM International. And some non-cloth, non-medical masks available in stores may look like medical masks — but aren't, experts say, so it's important for consumers to check the label.

Medical/surgical masks are graded by ASTM International. Experts caution that some disposable non-medical masks look similar but aren't certified. (CBC/Radio-Canada)

The ASTM has started a voluntary certification program for non-medical masks, but at this point, there aren't many certified non-medical masks available.

In an effort to better curb COVID-19 transmission, some countries, like Germany and Austria, have mandated medical-grade masks and respirators instead of cloth masks in public areas.

In many cases, they've been distributed for free or subsidized, said Fallis — a move he'd like to see Canada make. 

"I think that's a worthwhile investment because it's another way to bring cases down [and] to make higher-quality masks a little bit cheaper, particularly to people … [for whom] it's a financial burden to be purchasing masks," he said.

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