For months, as the COVID-19 crisis escalated and Canadians and Americans watched people across Asia increasingly wearing masks in public spaces, our health authorities stuck to their long-held policies, strongly advising against this.

That is, until Friday. That’s when the U.S. Centers for Disease Control reversed course, advising the public to use “cloth face coverings” to help slow the spread of COVID-19. They may have preferred to make this a quiet change on their website, but a characteristically bombastic press conference (and victory lap) by Donald Trump ensured that there was no saving face (no pun intended).

The Public Health Agency of Canada made the same policy change Monday, and I suspect that the World Health Organization will not be far behind. And with these reversals come an eroding in public trust in the very organizations we need people to trust the most, at the very moment when our collective survival most depends on that trust.

So what went wrong?

Let’s start with how this virus is transmitted. It travels in tiny water droplets expelled when people breathe (picture your breath on a winter morning), and especially cough or sneeze. Droplets are propelled up to six feet before they land (hence “social/physical distancing” advice). So it doesn’t take a rocket scientist to reason that a mask could reduce transmission by both blocking droplets coming out of (“droplets out”) and into (“droplets in”) someone’s mouth and nose.

Yet, despite an increasing number of countries espousing a public masking policy, the U.S. and Canada continued to resist. The common refrain was that there was no scientific evidence supporting this. Strictly speaking, this is true. Studies show that masks are effective at reducing virus transmission from patients when worn by health care workers and household contacts, but authorities contended that these settings were not comparable to daily life, and other viruses not comparable to the novel coronavirus.

They also pointed out a concern that if used incorrectly, masks could increase transmission rates. On the other hand, they ignored studies demonstrating that masks (even cloth masks) reduce both “droplets out” and “droplets in” (though cloth masks appear to be less reliable at blocking “droplets in”).

They also ignored a growing body of “ecological” data (studies comparing trends between populations) showing that countries that were effectively “flattening the curve” were the same ones that had enacted public masking policies. Although this alone is not proof, it was clear that there was a scientifically plausible argument to be made on both sides of the debate.

Yet authorities continued to ignore the other side. To make things worse, the same agencies aggressively promoted a strategy of social/physical distancing, which is based on a completely logical and sound argument, but suffers from the same lack of scientific evidence. This smacked of hypocrisy, and in the eyes of some, a Western disdain for the Eastern “cultural practice” of wearing masks in public.

But the most critical mistake was failing to adapt in light of emerging scientific evidence. The first report of asymptomatic transmission of the novel coronavirus was published about a month ago, and since then, estimates of the proportion of infections that are asymptomatic (up to 50 per cent in Iceland) and contribution of asymptomatic individuals to community spread have both steadily increased.

Again, members of the public made the very cogent argument that if authorities were recommending that people sick with the virus wear a mask to protect those around them, yet as many as half of people with the virus did not even know they had it, everyone should just wear a mask!

So we have come full circle. The balance of probabilities tells us that you should wear a mask in public, even if you’re perfectly well. You shouldn’t need an N95 mask (those are for health care procedures creating “aerosols”), and please don’t go out and buy surgical masks (health care workers need these for their high-risk exposures, and we’re running out).

Buy (or make) yourself a cloth mask. Remember — you’re doing it for others more so than for yourself (blocking “droplets out”) (maybe “reverse mask shaming” — shaming people for not wearing a mask — will even become a thing). Try your best to maintain physical distance, keep washing your hands, and always handle the mask as if it’s contaminated with the virus.

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In the age of rampant conspiracy theories and anti-science crusades like the anti-vax movement, it’s no fun to see our science-based organizations get a black eye. Hopefully this lesson will lead to a more transparent and nimble approach.

In fact — you can now find easy-to-follow instructions on how to make a mask out of T-shirt or a coffee filter (yes, a coffee filter) on the website of that venerable scientific institution — the Centers for Disease Control.

Dr. Samir Gupta (@SammyG_MD) is a respirologist, clinician-scientist, and associate professor at the University of Toronto. He chairs of the Canadian Respiratory Guidelines Committee of the Canadian Thoracic Society.