Non-medical masks can keep people with COVID-19 from spreading it, Tam says

OTTAWA — Wearing a simple cloth mask is a way for someone who might have COVID-19 without realizing it to avoid spreading the illness to others, Canada’s top public-health doctor said Monday.

Dr. Theresa Tam said the new advice, a shift from previous instructions, flows from increasing evidence that people with the virus can spread it without knowing they’re sick.

Masks worn this way protect others rather than the people wearing them, and don’t exempt wearers from all the other measures they should take against COVID-19, including physical distancing and regular handwashing, Tam said during a media briefing by federal officials.

“We are still in a very critical stage of Canada’s COVID-19 epidemic, and this is no time to relax our preventive measures.”

Medical masks still need to be preserved for front-line health workers, so cloth masks and other alternatives are the way to go, Tam said.

A non-medical mask can reduce the chance of respiratory droplets coming into contact with other people or surfaces — for instance, on a bus or at the grocery store, she said.

Scientific knowledge of COVID-19 continues to grow and it is clear that transmission of the virus is happening more often than previously recognized from infected people right before they develop symptoms, something called presymptomatic transmission, Tam said.

There is also evidence that some infected people who never develop symptoms are also able to spread the virus, a phenomenon known as asymptomatic transmission, she added.

Officials still do not know how big a role these two circumstances play in transmitting the virus, “but we know that it is occurring,” Tam said.

“Wearing a non-medical mask in the community has not been proven to protect the person wearing it. It is an additional way that you can protect others.”

The advice follows a similar recommendation made Friday by the U.S. Centers for Disease Control and Prevention.

Jim Bronskill, The Canadian Press