In response to a question on pandemic alert phase change, Dr Chan explained that the definition of WHO's influenza preparedness phases was developed against the backdrop of H5N1 avian flu.

在回答有关大流行警戒级别变更的问题时，陈博士解释说，世卫组织流感防备级别的定义是以h5n1禽流感为背景来制定的。

youdao

For the first time the W.H.O.raised its alert level from phase four to phase five on April twenty-ninth.

VOA: special.2009.05.06

But it has taken on new urgency,coming one day after the World Health Organization raised its global swine flu alert to Phase 4 on the six-point scale.

VOA: standard.2009.04.28

The World Health Organization says it needs to see clear evidence of sustained community transmission of the swine flu virus from person-to-person in at least two regions of the world before it raises its alert to the phase six pandemic level.

VOA: standard.2009.05.14

"This change to a higher phase of alert is a signal to governments, to ministries of health and other ministries, to the pharm industry and the business community that certain actions now should be taken with increased urgency and at an accelerated pace, " Chan said.

CNN: WHO raises pandemic alert to second-highest level

The WHO's "Phases of Pandemic Alert, " which has been in existence for five years, characterizes phase 5 as a human-to-human spread of the virus into at least two countries in one WHO region, signaling that a pandemic is imminent.

CNN: WHO raises pandemic alert to second-highest level