Dr. Theresa Tam, chief public health officer of Canada, said the supply of medical-grade masks must be preserved for health system workers and those looking after patients infected with COVID-19.
"The effectiveness of the use of non-medical masks hasn't really been well demonstrated," said Tam. "But I think that there may not be any harm in wearing it, if one uses it properly — it's not gaping, it's really well fitted and you practice hygienic measures."

