The HA/NA protein sequences of the influenza virus from 1914 to 2012 are studied and the early-warning signal indicator values (the differences between predictable and unpredictable portions) for influenza pandemic outbreak are worked out through the calculation of the actual and predicted frequencies of amino-acid pairs. It is concluded that the differences between predictable and unpredictable portions for the pandemic years are significantly smaller than those for the adjacent years. Furthermore, it is also verified that the mutations of influenza virus HA/NA protein will cause influenza pandemic.
Influenza epidemic, Mutation probability, HA/NA protein sequence
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