1918 : Spanish Flu

One of the most devastating pandemic in the History, with the Plague in Mediaeval Ages, is the flu known as "Spanish Flu", which made a final point to the WWI - millions of deaths worlwide, the amount is always unknown, but some cities as Philadelphia were hit by threatening waves.
The flu affected mainly young people. The lack of antibiotics and respiratory assistance explains the ratet of deaths. Its infectiousness looked highest, and the cloth/gauze masks were likely not an enough efficient protection against contamination. In public places of San Francisco and Philadelphia, as instances, masks were required. On pics and some short news movies, we can see how heavily covered were the nurses.