How close is too close in the age of COVID-19?
As countries, including Canada, slowly emerge from lockdowns, social-distancing rules have eased as authorities try to strike a balance between keeping people safe and being realistic while social interactions and commercial activities resume.
On Tuesday, England became the latest country to join the “one-metre” club as British Prime Minister Boris Johnson introduced the new physical-distance recommendation, paring it down to 100 centimetres from 200.
Currently, some countries — such as China, Denmark, France and Singapore are following the one-metre rule of the World Health Organization; while others fall anywhere between one and two metres.
In the United States, the CDC recommends a minimum of six feet or 1.83 metre.
The Public Health Agency of Canada follows the two-metre rule.
So, why the difference, and what’s safe?
Here’s what the experts said.
“Two metres is more a theoretical number based on our best assessment of how far droplets can travel,” said Dr. Alon Vaisman, an infectious-disease physician at Toronto’s University Health Network.
“It’s possible for droplets to travel further or shorter, depending on the individuals, but that two metres is the rough estimate of what it should be and what we recommend.”
While there’s a general consensus among scientists about the two-metre safe-distance rule, Vaisman said government policymakers don’t always base decisions on scientific evidence and often take into account other factors, such as practicality.
“If two metres is not practical for the majority of people where they work and live, you’re better off staying at one metre,” he said, maintaining that a two-metre distance strikes a “reasonable balance” between reducing risks and practicality.
According to Toronto infectious disease specialist Dr. Michael Gardam, up until a decade ago, the standard distance of isolation that was required for droplet-spread infections was actually just one metre. That optimal distance was based on clinical evidence from studies that go back to the middle of last century.
In 2009, the Centers for Disease Control and Prevention extended that to two metres during the H1N1 pandemic, based on experimental evidence in labs.
“Both clinical and experimental evidence are important, and one doesn’t trump the other,” said Gardam, the chief of staff at Humber River Hospital.
(Clinic evidence is based on findings from treatment of patients while experimental evidence derives from experiments in a controlled environment.)
Currently experimental evidence is suggesting that people can get airborne transmission of the COVID-19 virus when they create airborne aerosols while singing, coughing or breathing.
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“The problem is epidemiologically that doesn’t fit. We are not seeing evidence of airborne transmission. We are seeing large droplet transmission,” noted Gardam.
“With the case of the two-metre distancing thing, if you can, follow the precautionary principle, which is, until it’s absolutely proven there’s no risk, you should assume there’s a risk.”
Some health authorities also advise people to stay about two arms’ length from others, which Gardam said is not the most precise way to assert a social distance because shorter individuals, such as children, have shorter reach but still need to observe the safe distance.
“Safe distance doesn’t vary based on height,” Gardam said, noting that the concentration of particles dilutes with distance from the source.
“The further, the better.”
Colin Furness, an infection control epidemiologist and assistant professor at the University of Toronto, said he believed the U.K. government adjusted the recommended social distancing in order to make the practice “sustainable” in the new normal.
“We don’t know what effect this may have. People are not good at judging distance. We don’t have magic compliance in telling distance. It’s really about how safe people feel and trust (the distance),” Furness said.
The experts said Canada’s two-metre rule is conservative but appropriate, and Ottawa should stick to that approach.
“The public is going to find it confusing every time there’s a change,” Vaisman said.
“From a practical point of view, for them to buy your message from public health, changes will probably be more harm than good because you start losing credibility.”
Furness said social distancing is among many new rituals — such as wearing masks and washing hands — people need to keep observing and following in this new age.
“You can’t substitute one with another. You can’t take your mask off because you keep your social distance and think you don’t need it,” said Furness. “The stakes are too high.”
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