I have started getting flu shots now that I am retired. For years I chose not to do so on the logic that I did not want to pass up a chance to stay home from work, even if I was sick. And after all, it was “only” the flu that I would be getting, which is hardly more than a bad cold. Right?

Seriously, influenza is still a very dangerous illness worldwide, even if in the United States healthy people generally are not hugely affected by it. The World Health Organization estimates that from 250,000 to 500,000 people die annually from the flu. However, what we see today is a drop in the bucket compared to the influenza pandemic of 1918, which was then commonly known as the Spanish flu.

World War I was known as “The War to End Wars.” In terms of gross casualties, it was not as deadly as World War II, but a horrifying number of men were killed in the narrow system of trenches that stretched across northern Europe. Tactics had not kept pace with the development of armaments, and thousands of men were sent to their deaths “over the top,” to be mowed down by overlapping machine gun fire. About ten million men died during the conflict.

Bloody as the fighting was, more people died from influenza during World War I and just after it than died in the fighting. It infected 500 million people around the world, or about a quarter of the world’s population. The death toll during the pandemic is estimated to have been 30 to 50 million, or several times the number of soldiers killed during the War. (Some calculations put the number of fatalities as high as 100 million.) The majority of the deaths were from bacterial pneumonia, a common secondary infection resulting from influenza.

The mortality pattern held true in the United States. About 117,000 of our doughboys were killed during the war, but over 500,000 Americans died from the disease. Nothing we have seen in this country compares with it. Even what we are seeing this year pales alongside.

There have been different theories as to the origin of the epidemic. However, a major troop staging area and hospital in Etaples, France seems to have been the early center of the disease. The overcrowded conditions were ideal for the spreading of a respiratory ailment. The massive troop movements of World War I hastened its migration, and no doubt some soldiers carried it home with them.

One of the indirect effects of the epidemic was that much of everyday life was hampered. Even in communities where mortality was low, enough adults were infected that ordinary life came to a halt. When healthcare workers are too sick to nurse the ailing and gravediggers too ill to bury the dead, things have indeed reached a crisis.

You can imagine the psychological effects of the disease. Since one of every four persons was infected, it must have seemed like virtually everyone was sick. Likely a majority of households did suffer from it. And since flu is infectious, fear of catching it would have brought normal commerce to a screeching halt. People became afraid to go anywhere for fear of being infected. Churches, schools – any sort of social activity was affected by the threat of contracting the flu.

Strangely, when the epidemic finally began to wane, it sometimes did so very rapidly. Over 4000 Philadelphians died during the week of October 16, 1918; but less than a month later flu had almost disappeared from the city.