History of outbreak

In May 1977, an outbreak of flu took place in northern China including Liaoning, Jilin and Tianjin.^{[3][5][15][16]} 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.^[3] Clinical symptoms were relatively mild.^[3] Other areas in mainland Chinaand British Hong Kong were also affected in the following months.^[3][11]

In the same year, the H1N1 strain was detected in Siberia shortly after the outbreak in China, and then spread rapidly across the Soviet Union, which was the first country to report the outbreak to the World Health Organization (the People's Republic of China was not a member of WHO until 1981^[17]).^[1][4][5][6] Therefore, the pandemic was named "Russian flu".^[18]

In 1977, the Russian flu hit the United Kingdom.^[19] The virus reached the United States in January 1978.^[6][15] 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.^[2][6] Even though infections were seen in schools and military bases throughout the U.S, there were few reports of infection in people older than 26, and the death rate in affected individuals was low.^[2][6]

Since late 1977, the H1N1 strain has begun to co-circulate with the H3N2 strain in humans, as seasonal flu.^[1][3][18]

Virology

There have been various H1N1 strains.^[5] The 1977 H1N1 strain was almost identical to the strain in the 1950s, which was not circulating around the world until its reappearance in 1977.^{[1][2][3][4][5][6]} (Meanwhile, there had been some isolated report of other H1N1 strain such as the one in the early 1960s^[20]) This feature of the 1977 strain has been interpreted as an anthropogenic origin of the virus.^[5][21][22]

• It has been suggested by many researchers that the virus leaked to the public from a laboratory accident.^{[4][11][23][24]} The virus may have escaped from a lab attempting to prepare an attenuated H1N1 vaccine in response to the US swine flu pandemic alert.^[25] The World Health Organization, however, ruled out a laboratory origin in 1978 after discussions with researchers in the Soviet Union and China: their report stated that "the laboratories concerned either had never kept H1N1 virus or had not worked with it for a long time".^[3][5]
• Others have suggested that it resulted from a vaccine trial.^[5] The multiple source locations of outbreak made a single-laboratory origin less likely than a vaccine accident.^[5] Virologist Peter Palese claims the outbreak was the "result of vaccine trials in the Far East involving the challenge of several thousand military recruits with live H1N1," according to personal communication with virologist Chi-Ming Chu.^[14]
• The idea that the virus may have been a deliberately-deployed bioweapon appears unlikely and inconsistent with Soviet biological weapon research at the time.^[5]