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Discussion
Our analysis revealed dynamic reassortments between influenza A(H7N9) and A(H9N2) viruses since the outbreak of A(H7N9) virus infection in March 2013.To some extent, the continuous transmission of H7N9 in Chinese poultry has led to increasing diversity and new reassortment of A(H7N9) with local A(H9N2) strains. Our findings suggest that the re-emerged H7N9 infections may be triggered by new reassortment strains, such as those in the Guangdong/Hong Kong transmission of Cluster 3. In this regard, these infections may have implications for the traditional strategies of drug and vaccine development targeted against HA and NA genes [15].In particular, the new reassortments generated by A(H7N9) and local A(H9N2) strains may produce avian influenza virus strains that are more adaptive and have a higher pathogenicity in humans [16], emphasising the importance of continuously monitoring the A(H7N9) epidemic.
To date, 127 cases of A(H7N9) virus infections have been reported in January 2014, almost the same number as reported in the spring of 2013 (n=133) [5,6]. Notably, Zhejiang and Guangdong provinces and the Shanghai metropolitan area, where new reassortment of A(H7N9) strains is being identified, have been the worst affected regions in China in 2014 [1,17,18]. Although the case-fatality rate in January 2014 (24%, 31/127) is not higher than that seen in the spring of 2013 (29%, 39/133) [5,6], the rapidly increasing number of cases of A(H7N9) virus infection in these three regions may raise concerns as to whether there is an association between circulation of the new A(H7N9) reassortment strains identified and accelerated transmission of A(H7N9) virus in humans. Therefore, it is of the utmost importance to monitor the risk of a potential pandemic initiated by various influenza virus strains.
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