To get a fix on what that earlier pandemic can tell us about today’s crisis, I spoke with Mark Humphries, a historian and the director of the Laurier Center for Military, Strategic and Disarmament Studies at Wilfred Laurier University in Waterloo, Ontario. Professor Humphries’ books include “The Last Plague: Spanish Influenza and the Politics of Public Health in Canada.” Our conversation has been condensed and edited for clarity.

Most people believe that the Spanish flu was carried across Canada by troops returning from fighting in Europe during World War I. Is that how it happened?

There’s a popular perception that because we know that the war ends in November of 1918, that means somehow things are ramping down. But the reality is that the war effort really peaks in the fall of 1918. That includes the expansion of Canada’s war effort to create a force to go to Siberia to fight the Bolsheviks. They mobilized people across the country and that is what’s responsible for how the flu was seeded across the country.

It would have inevitably crossed the country no matter what and it probably would have happened over a period of several weeks rather than simply one week. It’s just that we can actually trace the spread in many local communities to those soldiers.

How quickly was the seriousness of the situation recognized?

Public health officials by this point were very experienced in tracking infectious diseases. And in many ways, what’s remarkable about the Spanish flu is how little worry it caused within professional circles. It was very much treated as just another of many different public health problems. And that, to me, is always the most remarkable thing when looking back at 1918.

The reason was that in 1918 you were far more likely to die of an infectious disease than today. Generally, we then had dozens of major infectious diseases that were constantly making the rounds in communities. And if you think about the war, it had by the fall of 1918 resulted in about 45,000 Canadian deaths by that point.

Why was the Spanish flu so lethal?

Nineteen eighteen was a very different time than today. Tuberculosis was rampant. The world was powered by coal in people’s houses as well as in industry and there were no scrubbers or anything like that on smokestacks. The baseline in terms of the everyday health of most working-class people was much lower. You’re dealing with a world in which you still had lots of children who developed rickets and other things like that.

So you mix all those things together, combined with overcrowding to a degree that is unimaginable today, and you create the perfect environment for a severe respiratory pathogen like the 1918 flu to run through the population.