Up until now, no cases of human-to-human transmission of the virus have been discovered.

到目前为止尚未发现人际间传播禽流感的病例。

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The WHO raised the alert level to Phase 4, meaning there is sustained human-to-human transmission of the virus causing outbreaks in at least one country.

世卫组织警戒级别提高为4级，这也意味着由病毒引起持续的人际之间的传播至少会在一个国家引起暴发。

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All prerequisites for the start of a pandemic have therefore been met save one: the establishment of efficient and sustained human-to-human transmission of the virus.

因此，发生大流行的所有前提，只差一个还没有满足：病毒在人与人之间确立有效而持续传播。

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But the WHO says there is currently no evidence of human-to-human transmission of the virus.

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In a statement, the WHO reiterated that there was not yet any evidence of human-to-human transmission of the virus.

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The WHO said investigations were being conducted into the likely source of the infection, the method of exposure, and the possibility of human-to-human transmission of the virus.

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