因为禽流感病毒可以通过变异在人与人之间传播，人们对病毒又不具备免疫能力，同时疫苗的研发生产需要花费数月时间，所以它被认为是威胁全球人类生命健康的一大敌人。

It is considered a global health threat, because it could mutate into a strain that is easily passed from person to person, people have no immunity to it, and a vaccine would take months to produce.

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