I have previously shared this little known, but factual, event on Hacker News. It is simply a Wikipedia article--the 1977 Russian Flu (https://en.wikipedia.org/wiki/1977_Russian_flu). This is not my statement, note this well dang, and read or argue with the editors of Wikipedia if you want (not me), but the following statement stands firm:
"Genetic analysis and several unusual characteristics of the 1977 Russian flu have prompted many researchers to say that the virus was released to the public through a laboratory accident, or resulted from a live-vaccine trial escape"
"Genetic analysis and several unusual characteristics of the 1977 Russian flu have prompted many researchers to say that the virus was released to the public through a laboratory accident, or resulted from a live-vaccine trial escape"