Looking back at an article from everyone's favorite expert, Dr. Anthony Fauci, from a 2008 study of the Spanish Flu in 1918-1919, it was determined that the real killer was actual bacteria which caused pneumonia.
Wonder if these lovely masks that trap everything around our mouths/noses might be contributing to bacteria in our systems? Of course we all know the answer to that.

Here's the article. Enjoy!
Bacteria were the real killers in 1918 flu pandemic | New Scientist