Evolution and Antigenic Drift of Influenza A (H7N9) Viruses, China, 2017–2019
Jiahao Zhang, Hejia Ye, Huanan Li, Kaixiong Ma, Weihong Qiu, Yiqun Chen, Ziwen Qiu, Bo Li, Weixin Jia, Zhaoping Liang, Ming Liao, Wenbao Qi
Abstract
S ince emerging in China in 2013, influenza A(H7N9) viruses have continued to circulate in mainland China, sporadically causing human infection (1-3). As of February 2020, a total of 1,568 laboratory-confirmed human cases and 616 related deaths had been reported, for a fatality rate of 40% (http://www.fao.org/ag/againfo/programmes/ en/empres/H7N9/situation_update.html). In mid-2016, a highly pathogenic avian influenza (HPAI) virus of subtype H7N9 emerged, and the number of cases in humans began to rise sharply during a fifth wave (4,5). Animal studies indicated that these HPAI H7N9 viruses are highly virulent in chickens and have gained transmissibility among ferrets (5-7). Also, the cocirculation of HPAI (H7N9) viruses caused high genetic diversity and host adaption (8), posing public health concerns.