Phase five is marked by human-to-human spread of the virus into at least two countries in the same area of the world.

VOA: special.2009.05.06

Phase four means that a virus has gained the ability to cause community-level outbreaks.

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