Originally Posted by narvik

I wonder if parallels could possibly be drawn from the 1918 "Spanish" flu (quotes from https://en.wikipedia.org/wiki/Spanish_flu)

[all bolding mine]


Regarding second wave of 1918 flu pandemic:

"This increased severity has been attributed to the circumstances of the First World War. In civilian life, natural selection favors a mild strain. Those who get very ill stay home, and those mildly ill continue with their lives, preferentially spreading the mild strain. In the trenches, natural selection was reversed. Soldiers with a mild strain stayed where they were, while the severely ill were sent on crowded trains to crowded field hospitals, spreading the deadlier virus. The second wave began, and the flu quickly spread around the world again. Consequently, during modern pandemics, health officials pay attention when the virus reaches places with social upheaval (looking for deadlier strains of the virus)."


And under the heading "End of the pandemic":

"Another theory holds that the 1918 virus mutated extremely rapidly to a less lethal strain. This is a common occurrence with influenza viruses: There is a tendency for pathogenic viruses to become less lethal with time, as the hosts of more dangerous strains tend to die out."