Scientists’ letter on airborne COVID-19 not accurate: experts
A group of 239 scientists and physicians urging the World Health Organization to recognize the potential for airborne transmission of the novel coronavirus has sparked debate over how COVID-19 is spreading.
But some Canadian infectious-disease experts say not to get hung up on the term “airborne,” and that the safety precautions we’re already taking to slow the spread of the virus are working.
“To the general public the word [airborne] can be pretty confusing, because it suggests that COVID is gonna come through the keyhole and get you in your sleep. And well, it isn’t,” said Colin Furness, an epidemiologist with the University of Toronto.
“No one is suggesting COVID behaves anything like measles. … That’s not the point [the scientists] are trying to make.”
In an open letter to the WHO published Monday, scientists across 32 countries called for the organization to revise its safety recommendations to mitigate possible spread of COVID-19 through aerosols — tiny, light particles expelled when people cough, sneeze or breathe that stay suspended in the air for longer periods of time.
The WHO currently classifies SARS-CoV-2 as a droplet virus, spreading through larger, heavier particles that can travel one to two metres before hitting the ground.
Furness says WHO is right, according to how we’ve seen COVID spread in clinical practice, but the scientists behind the letter have a point, too.
He said people release particles of all sizes when they breathe, and SARS-CoV-2 can be found in smaller droplets. But that doesn’t mean they are effective in trasmitting the virus, he added.
The scientists’ letter mentions a COVID-19 outbreak at a Chinese restaurant where customers at tables farther than two metres apart became infected. While the authors use that as an argument for COVID’s spread through aerosols, Furness said that’s not necessarily the case.
“It could be [evidence of aerosol spread] but it also could be that they touched the same thing. We don’t know,” he said. “Also one would need to explain why didn’t everyone in the restaurant get sick?”
“So WHO is right that there isn’t a clear case. And the scientists who signed that letter are right saying we do need to look at this … because it could have an impact on what we say is safe.”
Dr. Bonnie Henry, B.C.’s provincial health officer, praised WHO on Monday for “doing an amazing job trying to keep up with what’s going on,” and said she thought the scientists’ letter was “trying to foment a bit of controversy.”
Henry added that while COVID does seem to be released in small droplets as well as large droplets, we don’t know how potent those smaller particles are.
“Where there’s some challenges is how much is due to the small aerosols which are transmitted when I’m close to you, or the larger droplets that tend to fall out more readily,” Henry said. “So it’s really a bit of nuance, I think.”
Dr. Zain Chagla, an infectious disease physician and an associate professor at McMaster University in Hamilton, doesn’t believe the novel coronavirus is transmitting through aerosols, at least not to an extent we should be worried about. If it was, “we’d be in trouble,” he said. “We would have seen huge rates of transmission if this was a predominantly aerosol virus. We would have not been able to control it as well as we did.
“In reality, there is probably some degree of small aerosols that would carry COVID-19 in average day-to-day contact, but it’s probably very minimal.”
Chagla also believes the argument for aerosol versus droplet transmission is “more of a discrepancy on the exact scientific terminology” of what airborne actually means.
COVID-19 does have the potential to transmit through small particles when patients in hospital are undergoing “aerosol-generating procedures” like being intubated, Chagla said, and WHO also acknowledges that.
In those instances, health-care workers are given proper personal protective equipment, including N95 masks, which protect against small airborne particles.
But Chagla highlighted a specific case from early in the pandemic, before evidence of community spread, when healthcare workers treated a COVID patient in California without proper PPE.
Out of 121 health-care workers that treated the patient and performed “multiple aerosol-generating procedures,” only three got sick.
“So you had 118 individuals that … did not wear N95 masks which would be the only protection against aerosol viruses, and they did not get infected,” he said.
Chagla compared the situation to measles, which has a reproduction number of about 18 — meaning one infected person will infect 18 others. Measles particles can stay suspended in the air of a room for hours after an infected person leaves it, Chagla said, and you can catch the virus from much farther away.
COVID-19 has a reproduction number of two, Furness said, which is larger than other coronaviruses (0.5 for SARS and 1.5 for H1N1). So that could mean there’s more going on.
“COVID is doing something to be more infective than your average respiratory virus,” Furness said. “And I’m nowhere near saying it’s airborne, because I don’t think that’s an appropriate statement. But I think those aerosols, those smaller droplets that we’re disregarding, they might be important.”