In a significant departure from its previous advice, the Public Health Agency of Canada (PHAC) now says the novel coronavirus can be transmitted through small airborne droplets.

PHAC updated its virus transmission guidance on Tuesday as part of a larger overhaul of COVID-19 advice that also included a new recommendation that all face masks should contain three layers of material.

Previously, the agency had said that COVID-19 "most commonly" spreads through touching a contaminated surface or having close contact with an infected person who passes the virus along through droplets created when they speak, cough, sneeze or otherwise project from their mouth.

These droplets were thought to fall to the ground very quickly. The new guidance notes that this can take “seconds or minutes,” and that infection can also be transmitted through aerosols – smaller droplets that "linger in the air under some circumstances."

According to the new guidance, the droplets and aerosols can infect a person by being inhaled or by otherwise coming into contact with the mouth, nose or eyes.

Contact with contaminated surfaces, followed by touching the face without first handwashing, remains in the guidance as another potential method of transmission.

Canada’s chief public health officer referenced the new guidance Tuesday at a press conference with Prime Minister Justin Trudeau and other cabinet members.

"This is why we have been advising Canadians to try to avoid the three Cs – closed spaces with [poor] ventilation, crowded places with large numbers of people gathered and close contact situations where you can’t maintain physical distancing," Dr. Theresa Tam said.

"This pandemic is teaching us a lot about being flexible and adapting to new challenges."

Canada's new wording around aerosols is very similar to that of the World Health Organization, which first recognized aerosol transmission in July.

The U.S. Centers for Disease Control issued similar guidance in October, although it emphasized at the time that it still believes prolonged, close contact with an infected person is a much more significant source of COVID-19 spread.