The Great Influenza

While Vaughan believed the influenza virus threatened civilization, in fact, many viruses depend on civilization to survive. Measles, for example, will die out once all the humans in a community get infected and become immune. Influenza, however, doesn’t need humans around, since it can survive in birds.

Twenty years before the influenza pandemic, H.G. Wells wrote War of the Worlds, which involves aliens that temporarily take over the human race, only to be defeated by Earth’s infectious pathogens. Similarly, the suffering influenza caused would stop due to natural processes.

One process that helped end the pandemic was immunity, which people acquired after being infected. Though immunity didn’t completely stop the virus from spreading, it did slow down its explosive pace. By the Armistice of 11 November 1918, the virus had already almost disappeared from Philadelphia.

The other process that helped end the pandemic was the mathematical concept of “reversion to the mean.” Basically, because the 1918 influenza variant was so extreme in its virulence, and because influenza mutates so rapidly, it was only a matter of time before the variant mutated back to something with a lethality more like typical influenza.

Some claimed that conditions improved because army doctors at affected camps simply got better at treating influenza, but there’s no hard evidence for this. What is true, however, is that people struck later in the pandemic tended to become less ill. This was true both for residents in cities that were hit early and for whole cities (like on the West Coast) that were hit later.

By November, the virus had made its way around the world, and the second wave was more or less over, though the virus was not fully gone. The virus mutated again, and by December 11, there were still pockets of the U.S. with severe epidemics, even if things were much better overall. This third wave was still very lethal, just considerably less so than the second wave.

By early 1919, Australia was just about the only place in the world that had escaped the virus, largely due to rigorous quarantines of incoming ships. The virus did eventually escape from a ship of soldiers. Because the war was over, the newspapers were no longer censored, and so journalists wrote vividly of the virus’s devastation, even though Australia had a milder outbreak than the rest of the world. Survivors frequently compared their experiences to the Black Death.

Though the worst of the virus had passed, it still struck intermittently throughout spring 1919, and it remained powerful enough to do one last thing.