Phase 4 is characterized by verified human-to-human transmission of an animal or human-animal influenza reassortant virus able to cause "community-level outbreaks."
第4警戒级别是指，动物流感病毒或动物与人类流感重组病毒造成的人与人间传染，足以造成社区传染。
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Also, the Nigerian team noted, the existence of pandemic H1N1 in Egypt alongside H5N1 "raises the possibility of co-infection and the emergence of reassortant viruses."
The reassortant also has a higher yield via microcarrier culture. We could get the better anti-serum by immuning female goat, and selected suitable purification method of the anti-serum.