Pandemic H4N2 sub-type of Influenza A.
Coded only in 1971, though contact was first made in 1965. Commonly called "Hong Kong-4", though it is now believed to have originated in the Hunan province of China, many miles inland from Hong Kong.
It is believed that it was formed due to radiation mutation from nuclear weapons fall-out, either from Russia or northern China.
The first outbreaks occur in China in October 1965, and spread to Russia, India, Southeast Asia by Winter 1966. American (both continents) and European contact doesn't come until February 1967, due to early attempts at quarentine.
By Spring 1967, death tolls push 40 million, mostly in Asia and Europe. By the end of 1967, the population of Europe has reached a level unseen since the 1600s. America weathers the flu, but still loses 850,000 people, mostly in the remaining urban areas.
The final cases were reported by diplomats in South America in August 1967.