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. 2014 Jan;20(1):6–12. doi: 10.3201/eid2001.121848

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Significant points in the history of influenza viruses that have contributed to the emergence of influenza A(H1N2) viruses in human and swine populations. The bird and swine symbols on the timeline indicate when transmission appeared to occur directly from either avian or swine source into the relevant population. The bird symbols on the 1957 and 1968 time-points indicate that the circulating viruses of the time reassorted with viruses of an avian source resulting in novel subtypes. Significant events leading to the emergence of A(H1N2) in the human population are above the timeline and in swine below the timeline. A(H1N2) viruses appearing in both human and swine populations are indicated in boldface. Genotypes of A(H1N2) emerging in the human population are: 1989 (China), human A(H3N2) virus with hemagglutinin (HA) from human A(H1N1); 2000 (worldwide), same genotype as 1989 virus; 2009 (India), human A(H3N2) virus with HA from A(H1N1pdm09); 2012 (United States), human-like H1, A(H1N1pdm09) matrix, remainder swine H3N2 triple reassortant. Virus origins: Cl-sw, classical swine; hu, human; sw, swine; av, avian; hu-like, human like; double, double reassortant, tripleR, triple reassortant.