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Monthly distribution of influenza C viruses in Japan between 1988 and 2014. The number of influenza C virus isolates was obtained from our previous reports: Matsuzaki et al. (17, 19, 20, 21, 22, 24, 32), Kimura et al. (18), and Tanaka et al. (25). The colored open squares indicate the representative reassortant viruses that emerged during influenza C virus epidemics.
