Generals often talk about the “fog of war.” It speaks to the uncertainties in the thick of battle, when decisions have to be made yet essential information is not at hand, from the position of the enemy to the weaknesses of one’s own forces. Each bit of new intelligence is a step on the road to victory.

The speed at which science has steadily penetrated the fog surrounding COVID-19 has been remarkable. As the battle goes on, new evidence constantly emerges, and knowledge of the adversary grows. There is still uncertainty but, every day, there is less.

As Canada reopens its economy – with different provinces, and even parts of provinces, moving at varying paces – the question of wearing masks in public places is now at the fore. The science is not entirely settled. However, there is considerable evidence that a mask can act as a kind of shield, lessening the likelihood of transmitting of the virus.

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As such, it is time to make masks mandatory in crowded, indoor public spaces.

In the course of the coronavirus war, Canadians have faced an array of shifting rules and recommendations. Some things that were once merely advised, such as isolation for returning travellers, soon became mandatory rules. Other things, such as mask-wearing, are strongly recommended – yet in many places are still not required.

That makes it difficult for even the most dialled-in citizen to know what to do.

I’m at the grocery store. Am I supposed to wear a mask? Many people are not. I’m on the bus. Am I supposed to wear a mask? Many people are. At some retailers, all employees are masked; in others, they aren’t. In some stores, customers must wear a mask; in others, none do.

It’s time to replace a mass of vague and confusing suggestions with rules that are clear and simple. A mask should be required outside of the home wherever people are in relatively close contact, notably in stores and on public transit.

Masks are not a panacea. Physical distancing, washing your hands and isolating if you have symptoms are the three essentials. But mounting evidence indicates that masks can cut the risk of spreading COVID-19. The Toronto Transit Commission on Wednesday officially made masks mandatory as of early July. That should be a national example.

A group of experts recently called on top health officials to make masks broadly mandatory. They argued there is strong evidence of the efficacy of masks, and little evidence of any downside. Research from Germany – where various regions adopted mandatory masks at different points in the outbreak – is clear. In parts of Asia, masks have for years been widely used by anyone who is sick.

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Most of all, masks are an act of citizenship. Evidence suggests that masks, when worn by someone who unknowingly has the virus, reduces the odds of spreading it to someone else. At least some infections are believed to come from people who are asymptomatic or presymptomatic, and if many more people wore a mask when in a confined space, we’d all be better off.

However much of an inconvenience it might seem to be at first, consider the mask as an extremely cheap insurance policy against future waves of infection, and the need for another calamitous lockdown.

Finally, making masks mandatory in confined public spaces is not about punishing people. Ontario Premier Doug Ford this week said he “highly, highly” recommends masks – but would not make them mandatory because it would be too difficult to enforce. But this isn’t about enforcement through mass policing. It’s rather about sending a clear message to Canadians, and giving retailers and others permission to insist that people follow the rules. This is about a collective understanding of how we can help one another.

Public-health authorities in each province, and in each region, should have the power to order that masks be worn in selected public places. And if they determine it is safe to do so, public health should have the power to rescind those orders.

In parts of the country with few or no new cases of the virus, a mask order might not be necessary. In others, it clearly is. Let’s leave it to the experts, not politicians, to decide.

Canada has made big strides against COVID-19, because Canadians have largely adopted physical distancing and hand washing. Masks must now become part of our arsenal.

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