World Health Organization Director-General Margaret Chan said the alert level was stepped up because influenza viruses are unpredictable and can spread quickly around the world.

VOA: standard.2009.04.29

because all we konw now it's orange alert, the alert level has gone up or gone down We don't really know what it goes on behind the scene.

我们都知道现在是橙色警报，警戒线时高时低,我们真的不知道,事情背后是如何处理的。

普林斯顿公开课 - 国际座谈会课程节选

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