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

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