The authors of a new paper that found increasingly concrete evidence that COVID-19 is “predominately” airborne say that we need to be focusing on preventing infections in indoor settings, and rethinking how ventilation systems either help spread or dissipate the virus.
A Lancet report published Thursday from epidemiologists and experts across both Canada, U.S. and the U.K. found an overwhelming amount of evidence that the disease was spread through aerosols — tiny airborne particles that come from people’s mouths when they breathe, talk or cough.
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According to University of Toronto Professor Dr. David Fisman, one of the authors of the study, the results of the report come as an important implication for experts and governments to consider more stringent measures public health control measures in indoor spaces.
Public health guidance on the spread of COVID-19 has, for the most part, been widely focused on direct contact with others and transmission via water droplets. The evidence from Fisman and his colleagues’ review, however, points to aerosols as potentially being the main mode of transmission for the virus.
“So there’s a lot of lines of evidence leading up to this final nail in the coffin of this contact droplet idea,” said Fisman. “And this is good news in a sense — it explains a lot about the epidemiology of this disease.
“That explains why we have these huge explosive outbreaks in places like church choirs and karaoke bars and spin studios, where people are vocalizing and creating a lot of aerosols.”
New or refocused measures to address the spread include a focus on breathing fresh air either through ventilation or moving activities outside, said Fisman. Other measures could also include using more air cleaners equipped with HEPA filters or better respirators — particularly in high-risk, essential and healthcare workplaces — in order to prevent people from inhaling aerosols.
Several of Fisman’s co-authors on the paper also shared their thoughts on the evidence they found.
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University of Colorado professor Jose-Luis Jimenez cited several pieces of evidence he and his team used for the report on Twitter Saturday.
“Transmission is 20 times more efficient indoors than outdoors,” wrote Jimenez, who cited a review from The Journal of Infectious Diseases.
13/ FOURTH LINE OF EV.: transmission is 20 times more efficient indoors than outdoors.
Same gravity indoors and outdoors, large droplets do the same in either (can't explain difference)
Huge aerosol dilution outdoors vs. trapping indoors can explain ithttps://t.co/1c6KUO6AUE
— Jose-Luis Jimenez (@jljcolorado) April 18, 2021
Zeynep Tufekci. a professor at the University of North Carolina at Chapel Hill, said that because the disease was “predominately airborne,” it doesn’t mean masks and social distancing were useless, but that now they have better ways at mitigating infections now that they have a stronger grasp on how the virus is transmitted.
Why this really matters. This isn’t quibbles at the margins. Its an incorrect paradigm being replaced. Some things overlap between the two, but not everything does and thus there will likely be many real changes going forward that affect *other* respiratory pathogens as well. https://t.co/ggBG3QnNLu
— zeynep tufekci (@zeynep) April 16, 2021
According to Fisman, the issue of pre-symptomatic transmission of COVID-19 — how the virus is spread before a patient starts to exhibit symptoms — also “strongly implies” aerosol.
“The way this ties to pre-symptomatic transmission is you’re not coughing when you’re symptomatic by definition, right? You may feel well enough to go to your choir, practise at a karaoke bar and be singing — and that creates orders of magnitude more aerosol than just quiet breathing,” he said.
In January, hundreds of doctors, scientists and experts from across Canada all called for more aggressive measures to stop the airborne spread of COVID-19.
In an open letter address to the country’s top doctor, health minister and all of the provincial premiers and medical officers, the experts urged public health messaging to more strongly warn of the risks of being in enclosed spaces. They also called for more stringent inspections and upgrades of ventilation systems in areas like schools and long-term care homes, as well as essential institutions.
The World Health Organization and Public Health Agency of Canada have recognized the possibility that COVID-19 can spread by aerosols, though those experts and doctors — including Fisman — have all said that Canada needs to be acting more proactively to prevent such spread.
