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Last week, Canada’s top doctor said that if we’re not sick, or haven’t been around someone with a confirmed case of COVID-19, we shouldn’t wear a mask. “Putting a mask on an asymptomatic person is not beneficial, obviously if you’re not infected,” she said.

This week, Dr. Theresa Tam did a complete about-face: actually, the use of non-medical masks can help to control the spread of COVID-19, she said. “Wearing a non-medical mask, even if you have no symptoms, is an additional measure that you can take to protect others around you in situations where physical distancing is difficult to maintain, such as in public transit or maybe in the grocery store.”

In normal times, a week is not a long time for a public health official to totally reverse a previous policy recommendation. But when the world is in the midst of a deadly pandemic, when a cough from one unknowingly infected person can lead to exponential numbers of infections, a week is a painfully long time.

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Countless Canadians have been taking transit, working essential jobs or stopping into stores for necessary food and medicine – all with their mouths and noses uncovered, heeding what was then the advice of Canada’s Chief Public Health Officer. There’s no way of knowing how much virus was shed during that time.

Dr. Tam’s earlier contention that masks are useless on asymptomatic people was outdated the moment she said it. (To be fair, the World Health Organization still maintains masks are only necessary for healthy people when taking care of a sick person.)

A letter published by a group of physicians in Germany in late January outlined a case of apparent transmission during the incubation period. A case study from February chronicled an asymptomatic 20-year-old Wuhan woman who infected five of her relatives without ever developing symptoms. Research published in March suggested that undocumented infections (meaning not-yet-diagnosed, mildly symptomatic or asymptomatic carriers) were the source of nearly 80 per cent of documented COVID-19 cases. All of that material was published before Dr. Tam said, in late March, that “there is no need to use a mask for well people.”

The purpose of a mask on an asymptomatic person is less to protect the wearer from everyone else than it is to protect everyone else from the wearer. That’s why, in a public health emergency, widespread adoption of masks is so important. It’s also why other countries, including Austria, South Korea, Slovakia, Czech Republic, to name a few, began coupling physical distancing directives with recommendations to wear masks in public weeks or months ago.

There are handfuls of studies of varying scopes and methods that suggest that even homemade masks (which, importantly, preserve medical masks for front line personnel) offer some benefit in mitigating viral shedding. And while it is true that precise characteristics of the virus is not yet fully understood, a weighing of available evidence – on the nature of COVID-19 spread, on the efficacy of masks and on our recent proclivity toward adopting as many preventative measures as possible – should have made a recommendation for face masks in Canada a no-brainer.

When pressed by journalists Monday, Dr. Tam attributed her reversal to a review of evolving evidence. Yet it is unclear to which precise evidence she refers, and why that evidence was more compelling than the collection of previous published research.

There may have been some concern from public health authorities that recommending masks for general use would have sent people snapping up medical masks, depleting supply. Dr. Tam also alluded to the idea that masks can confer a sense of invincibility; that mask-wearers might feel “protected” enough to ease up physical distancing guidelines. But both issues can be neutered with clear, unequivocal public health instructions: Here’s how you wear your mask. Here’s how you take it off. Here’s what you don’t do while wearing a mask. And please, homemade masks only.

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In a time of crisis, the public’s faith in those calling the shots is absolutely critical. Health authorities are asking a lot of people – to stay home, to avoid seeing friends and family, to eliminate so many simple, easy pleasures. If people can’t trust the individuals issuing the directives, they will be far less inclined to follow their instructions.

Dr. Tam has backtracked before – on the risk posed to Canadians by COVID-19, on the usefulness of travel restrictions and, now, on the efficacy of masks for asymptomatic individuals. And while we can’t expect health authorities to be omniscient, we can expect them to be direct, to explain their work, to produce their evidence and to offer some humility when they get things wrong. That can go a long way in establishing, or repairing, trust. Dr. Tam has some work to do.

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