Canada has quietly revised its guidelines on how COVID-19 spreads to include the risk of aerosol transmission, weeks after other countries and international health organizations acknowledged the airborne threat of the coronavirus.
The Public Health Agency of Canada (PHAC) updated its guidance without notice this week, making mention of the risk of transmission from aerosols — or microscopic airborne particles — for the first time.
“SARS-CoV-2, the virus that causes COVID-19, spreads from an infected person to others through respiratory droplets and aerosols created when an infected person coughs, sneezes, sings, shouts, or talks,” the updated guidance said.
“The droplets vary in size from large droplets that fall to the ground rapidly (within seconds or minutes) near the infected person, to smaller droplets, sometimes called aerosols, which linger in the air under some circumstances.”
The federal agency’s guidelines previously said the virus spreads only through breathing in respiratory droplets, touching contaminated surfaces and common greetings like handshakes and hugs.
“We are continually reviewing new evidence and research as it emerges during the pandemic, and this new evidence guides our response to Canadians,” a spokesperson for PHAC said in a statement to CBC News late Wednesday.
“We are committed to continuing to keep Canadians informed of the latest available scientific evidence and expert opinion, so they can make informed decisions to keep themselves and their family safe and healthy.”
‘Pretty major’ change
“This is pretty major,” said Linsey Marr, one of the top aerosol scientists in the world and an expert on the airborne transmission of viruses at Virginia Tech. “The big difference now is that ventilation is important — distancing alone is not enough.”
CBC News pressed the federal agency last month on why it still made no mention about the risk of aerosols despite other international agencies doing so.
The U.S. Centers for Disease Control and Prevention (CDC) updated its guidelines in early October to include that COVID-19 can sometimes be spread by airborne transmission, after mistakenly posting and later removing a draft version of guidelines in late September.
The World Health Organization also came under fire in July after 239 scientists from 32 countries wrote an open letter calling on the United Nations agency to update its messaging on the risk of airborne transmission of the coronavirus.
Update came after new mask advice
The update to PHAC’s guidelines came after Canada’s Chief Public Health Officer Dr. Theresa Tam recommended the use of three-layer non-medical masks Tuesday to prevent the spread of COVID-19 ahead of winter weather that could bring more people together indoors.
“This is an additional recommendation just to add another layer of protection. The science of masks has really accelerated during this particular pandemic. So we’re just learning again as we go,” she said Tuesday.
“I do think that because it’s winter, because we’re all going inside, we’re learning more about droplets and aerosols.”
Marr said that updated PHAC guidance on three-layer non-medical masks was in line with the threat of aerosol transmission.
“If we were only concerned about large droplets, then pretty much almost any piece of single layer of fabric would work,” she said.
“But because we are concerned about aerosols, then we do need to think about the quality and fit of our masks and we know that having multiple layers improves the filtering performance of masks.”