The B.C. Centre for Disease control has finally updated its website to acknowledge COVID-19 is spread by aerosols, not just infected droplets that can only carry a few metres.
The World Health Organization recently made a similar change.
Aerosols are much smaller particles and can drift in the air like smoke. They disperse quickly outdoors, but not in poorly-ventilated indoor settings.
It’s a message hundreds of scientists have been sharing for nearly a year — most recently in an article published in The Lancet which argued the virus was “predominantly” spread by airborne transmission.
“It’s not something new. This is something we thought was true, we behaved as if it was true,” Dr. Brian Conway, medical director of the Vancouver Infectious Diseases Centre, told Global News.
“It reinforces where the public health guidelines are right now in terms of helping us understand why getting together with people indoors, especially at this stage of the pandemic, is even more dangerous than we might have appreciated.”
Until recently, the BC CDC’s “how it spreads” webpage had stated that the virus could both be spread by small droplets that hang in the air and larger droplets, but that “the majority of COVID-19 infections are spread from one person to another through larger droplets.”
Along with directly using the term aerosol, the updated language now that “Indoor accumulation is greater when more people share a space, spend more time together, or exercise, sing, shout, or speak loudly. These conditions can lead to COVID-19 transmission.”
Asked about aerosol transmission at her April 22 briefing, prior to the website language change, provincial health officer Dr. Bonnie Henry maintained the province had always focused on both small and large droplet transmission.
“We have always said that different size particles can carry virus, but we also know that … the virus survives more or less well, depending on the size of the particle,” she said at the time.
“We have recognized that smaller particles can transmit this virus, particularly in situations where we’re talking about which are indoors. When you’re in close contact with somebody, where you’re talking loudly, where you’re not wearing a mask, there’s poor ventilation that is unequivocal.”
Conway said the move is a recognition of the same science that has led to public health guidelines promoting outdoor activities, and reinforces the need to ensure indoor activities are done in places with good ventilation.
“Indoors we now know its not only the big droplets but the small aerosols that will hang around for a long period of time, especially in areas that are poorly ventilated, and lead to an increased risk of transmission,” he said.
Conway said the priority must now be on accelerating vaccinations as much as possible, and deploying more testing to identify virus hotspots..
He said the public also needs to double down on adhering to public health guidelines, particularly those regarding gathering indoors, over the coming weeks.
In January, hundreds of doctors, scientists and experts from across Canada penned an open letter to federal chief public health officer Dr. Theresa Tam, her provincial colleagues, federal Health Minister Patty Hajdu and the nation’s premiers calling for aggressive measures to stop the airborne spread of COVID-19.
The letter called for stronger public health messaging to warn of the risks of enclosed spaces, along with stricter inspections and upgrades for ventilation systems in places like schools, long-term care homes and essential institutions.
— With files from David Lao