What can be learned from 1918 flu pandemic
It certainly wasn’t during the influenza pandemic of 1918, which lasted from January 1918 to December 1920, and infected one-third of the world’s population, or about 500 million people, leading to about 50 million deaths — about half a million of which were in the United States.
In the 1918 flu pandemic, not wearing a mask was illegal in some parts of America. What changed?
https://edition.cnn.com/2020/04/03/americas/flu-america-1918-masks-intl-hnk/index.html