[1][2][5][6] 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,[4][5][7][8][9][10] or resulted from a live-vaccine trial escape.
[3][5][12][13] The strain was isolated and determined by Chinese researchers to be H1N1, which mostly affected students in middle and primary schools who lacked immunity to H1N1 virus.
[6][12] The first outbreak in the U.S. was reported in a high school in Cheyenne, where the clinical attack rate was more than 70% but involved solely students.
[1][2][3][4][5][6][11] This feature of the 1977 strain has been interpreted as pointing towards an anthropogenic origin of the virus, and the pandemic is the only documented human epidemic believed to result from research activity.
In 1977, Chinese researchers found uneven attack rates among different groups of students, as well as many mild and asymptomatic infections.