More scientists now believe COVID-19 spreads primarily through the air

TORONTO — An increasing number of doctors and scientists believe COVID-19 is primarily spread through the air and that public health measures need adjusting to reflect the new evidence.  

This month, studies in three prominent medical journals — the Lancet, the British Medical Journal and the Journal of the American Medical Association – each made the case that aerosols are the dominant mode of transmission of COVID-19 and that improved ventilation will help keep us safe.

“We found, without any doubt, there was strong evidence that not only does it travel in the air, but that the airborne route of transmission is dominant,” Dr. Trisha Greenhalgh, a professor of primary care at the University of Oxford, told CTV News.

“What that means is that most people who catch this virus, catch it by inhaling it in the air that they breathe.”

Greenhalgh is the lead author of “Ten scientific reasons in support of airborne transmission of SARS-CoV-2” published last week in the Lancet. In the report, Greenhalgh and her colleagues argue high incidence of super spreader events, COVID-19 spread in quarantine hotels, and asymptomatic spread of COVID-19 all point to airborne transmission of the virus.

Greenhalgh likened aerosol transmission of COVID-19 to second-hand smoke, which can linger in the air.

“It’s a good analogy,” she said. “If someone was smoking in the room, how long would you stay in the room? Probably not very long.”

Contrary to this updated information, the World Health Organization indicates that the virus is primarily spread through large respiratory droplets, rather than aerosols that can stay in the air for several minutes. When it comes to aerosols, the WHO only suggests that transmission of the virus is “possible,” while specifically mentioning transmission during choir practice, in restaurants and in fitness classes.

Similarly, a WHO-funded study published last month as a pre-print indicated “the lack of recoverable viral culture samples of SARS-CoV-2 prevents firm conclusions to be drawn about airborne transmission.”

While the WHO still believes aerosol transmission is inconclusive, doctors on the ground say patients are coming to the hospital with infections where airborne transmission is one of the few explanations.

“One person told me: ‘I didn’t take off my mask so how did I get this?’ Other people that you ask will say they only really took one trip,” said Dr. Alex Patel, a critical care physician in Toronto. “I remember one case just last week where they said they really only went to a small grocery store. They didn’t really do much else.”

Doctors and scientists have been pointing to aerosol transmission of the virus for months. In January, Masks4Canada, a group of doctors, professionals and citizens advocating for mask use, issued an open letter calling on federal health officials to update their guidelines to “reflect the science” that shows COVID-19 spreads through the air. 

Back in July, a group of 239 experts penned a similar open letter to the WHO calling for the agency to update its guidance to reflect airborne transmission.

For their part, both Health Canada and the U.S. Centers for Disease Control and Prevention updated their guidance in the fall to acknowledge the spread of COVID-19 through the air.

“I think the transmission of COVID-19 by aerosols is gaining importance and there’s mounting scientific evidence that it’s happening,” said Marina Freire-Gormaly, a mechanical engineer at York University.

If health officials alter their guidance to further acknowledge aerosol transmission, scientists argue more attention should be put on improving ventilation in buildings and elevators rather than improved cleaning measures.

They also argue people should be wearing more fitted masks to control the spread.

“It’s really important that the air that you’re breathing in has as much barriers as possible and also the air that you’re breathing out has as many barriers as possible,” Freire-Gormaly said. “If you have access to a higher-quality mask, that’s important.”

With this new information, Greenhalgh urges people to get outside to protect themselves from the virus’ spread.

“The most important message I think is ventilation,” she said. “If there’s one thing I get you to remember, be outdoors as much as possible. If you must be indoors, have the windows open.”


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