Quebec Flu

The Quebec Flu (largely known as the Beckie Flu in America) was a devastating influenza pandemic that broke out during the Great World War. It killed millions, hampered the war efforts of every combatant nation, and ended with the production of the Cleansing Vaccine by the Republican Union's Office of Health & Wellness, samples of which were later reverse-engineered and produced in most countries around the world. Though it's high tide was around the 1910s, the Quebec Flu would continue to kill many citizens of impoverished, isolated, or backward nations well into the 1930s and 1940s. While the American government and media always blamed Europan-governed Quebec as the original home of the pandemic, in all likelihood it originated somewhere in New York or Pennsylvania, thanks in part to the filthy working and living conditions afford to the Inferiors of Society by the Economic Clans and the Office of Racial and Religious Affairs. 
Although it killed half its victims, it was not merciful to survivors either. It counted future ORRA Supreme Chief George Patton among the infected, and it cost him the use of his legs, a side-effect that would haunt him and emasculate him for the rest of his life. This lead to the pursuit of ridiculous, often insane methods to try and regain their use, such as the failed breeding of human-ape hybrids, and culminated with his attempted hijacking of Charles Dexter Armitage's Worm Cult during the attempted mass-sacrifice ritual of the residents of the Congo Basin by the Congo Dam Authority.