@fatsam Very interesting. But most of this question was settled about ten years ago when it was discovered that disease-causing viruses survive and propagate best at very low and very high humidities. It's a U-shaped curve.

This answered the question of why do diseases like flu do well in the warm humid tropics and in winter in the U.S.A. In the U.S., in winter, furnaces come on drastically reducing indoor humidity. After learning this, for years now, I run humidifiers all winter. Instead of 12 to 15 percent indoor humidity, our house sits around 35 to 45 percent.

This also makes the house much more comfortable and allows us to run a lower indoor temperature (66 to 68F) while remaining comfortable. (You feel colder if the humidity is super low.)