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

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.  

"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.