TORONTO -- Some of Canada's top provincial doctors are downplaying new concerns from hundreds of scientists that physical distancing and frequent handwashing are not enough to fully protect against airborne transmission of the novel coronavirus.

In an open letter to the World Health Organization (WHO), 239 scientists in 32 countries argued that particles smaller than what has previously been reported can carry SARS-CoV-2, the virus that causes COVID-19, posing more of a danger than public health officials have been warning against.

However, in a news conference on Monday, B.C. provincial health officer Dr. Bonnie Henry said the letter is controversial.

"When you're in close contact with someone… particularly if you're indoors where there's poor ventilation and you're coughing or sneezing or singing or hugging or dancing, those are the situations where you're much more likely to transmit this virus, regardless of what size particle that you're breathing in," Henry said.

Henry said that microdroplets of airborne viruses such as measles and smallpox can float in the air for hours, move down hallways and even through ventilation systems, but the novel coronavirus appears to spread predominantly through larger droplets, according to Henry. She said that transmission of the virus requires more moisture and closer contact between people.

"We know that there is a gradation of how droplets come out when somebody coughs or sneezes or talks, and it is a smaller ones that can be breathed deep into the lungs, and it's the larger ones that are often deposited up in the back of the throat or in the upper part of the lungs," Henry explained.

"But we know that the amount of … moisture the virus needs to stay alive is a bit more for some of these viruses like influenza and COVID," she added.

Since the start of the pandemic the WHO has maintained that the droplets that carry SARS-CoV-2 are spread through actions including coughing, sneezing and speaking, and recommends that people keep a one-metre distance from others. Many countries, including Canada, have gone farther, recommending a physical distance of two metres.

The WHO said Tuesday that it has been in constant discussions with many of the letter’s signatories since April and is looking into the possible role of airborne transmission of COVID-19.

The organization said it has looked at a number of different ways the virus could be contracted including through inanimate objects, fecal-oral transmission, droplet, aerosol, mother-to-child and animal-to-human to "try to consolidate the growing knowledge around transmission." It will release a scientific brief in the coming days on its findings.

"This is a respiratory pathogen and so it is important that what we know fits into the guidance that we have, which is why a comprehensive package of interventions are required to be able to stop transmission," Dr. Maria Van Kerkhove, head of the WHO's emerging diseases and zoonosis unit, said in a press conference.

Henry said the novel coronavirus is "not transmitted long distances in the air column," but a previous American study found signs that the smallest microdroplets can travel beyond the two-metre limit.

"Where there's some challenges is how much of it is due to the small aerosols that are transmitted when I'm close to you, or the larger droplets that tend to followed more readily and how much of it do I breathe deep into my lungs and how much of it is deposited in the upper airways," Henry said.

The debate over droplets has been playing out since the pandemic began. Toronto infectious disease expert Dr. Isaac Bogoch told CTV News Channel on Monday that "there's a spectrum between droplet and airborne" viruses.

"It's a bit of a false dichotomy to say something is one or the other, but [this] infection really falls closer towards the droplet end of the spectrum, and when we use personal protective equipment to protect us against droplets and contact, we're safe," Bogoch said.

Bogoch said the open letter regarding airborne transmission of COVID-19 does not provide any new information about the virus.

"We're just rehashing the same arguments that we've heard throughout February, March, April, up until now. I'm not quite sure what the fuss is all about," he said.

The WHO reinforced that regardless of how the virus is transmitted, physical distancing measures and the use of face coverings have shown to help slow the spread.


Henry wasn't the only public health official to downplay the risk of airborne transmission of the virus, even as evidence mounts that it is possible.

In one study cited as an example in the letter, droplets were found to be the most likely source of transmission among three dining parties at a restaurant in China, in a case where surveillance video footage showed neither direct nor indirect contact between the groups.

Quebec's chief public health officer Dr. Horacio Arruda acknowledged Monday that there is some evidence the coronavirus may be airborne, but insisted that is not the principal transmission vector.

"Most of the transmission -- if not more than 95 per cent -- is going to be done by droplets because that's what the epidemiology told us. It doesn't mean that in certain situations there is no aerosols… So I would say that there is a debate on this," Arruda said during a news conference. "[But] I think that the issue is around droplets, not aerosols."

While there remain various unknowns about COVID-19, Ontario Minister of Health Christine Elliott said she is "satisfied" with current evidence that the virus is not spread when physical distancing is maintained.

"In terms of people respecting social distancing, being out on patios right now, the public health is satisfied that that's not going to transmit COVID. But we have to be concerned about indoor establishments," Elliott said on Monday.

Elliot said Ontario is focused on contact tracing as it continues to reopen its economy and said the province's declining case numbers show that current public health measures are working.

However, she said the province will evaluate its protections as more medical information regarding COVID-19 is confirmed, adding that airborne transmission of the virus "definitely will be borne in mind."

Henry said B.C.'s approach to COVID-19 involves several different measures of protection that prevent transmission of both small and large droplets. She said that this includes various types of personal protective equipment for health-care workers, physical distancing and non-medical face mask for the public.

"In a number of the food production places where we had outbreaks early on, once we put in place measures like plexi-glass barriers, like wearing medical masks or non-medical masks, even ensuring we have safe distances between people, we stopped the transmission of this virus," Henry said.

However, Henry said the province will continue looking at its transmission data and may enforce additional measures if cases begin to spike.

"The best way to protect people is making sure that sick people stay away from others, making sure that we are keeping our safe physical distancing [and] putting in place the administrative things to reduce the number of people in that environment," Henry said.

In Bogoch's view, Canada has proven that the current precautions and restrictions have slowed the spread of the virus.

"We're using personal protective equipment to protect us from droplets and contact transmission of this virus… and when we use droplet precautions -- the right mask, the right gloves, right down the right eye protection -- we were using it properly and we're not getting this infection," Bogoch explained.

While some provinces may take further safety precautions, Bogoch said there is currently no risk that the virus will be contracted through airborne transmission.

"If someone had COVID-19, they were in a room, then they left the room and if someone just went into that room an hour later and they just stood there, they're not going to get COVID-19," Bogoch said.

With files from's Ryan Flanagan