The Onset of Pneumonic Influenza in 1918 in Relation to the Wartime Use of Mustard Gas

This is an academic paper from 1947 discussing the probability that mustard gas used on the Western Front in 1918 caused a mutation of the (milder) first wave virus carrying "Spanish Flu" into a much more deadly second wave. The paper is very interesting and useful, since as well as tracing the probability of this having happened, it also describes apparently very accurately and in detail how the virus spread around the world