Six phases of swine flu pandemic

The WHO has six phases of pandemic alert to access the potential for new global flu outbreak.

Phase 1:
There are no viruses circulating in animals that have been reported to cause infections in humans.

Phase 2:
An animal flu virus has caused infections in human in the past and is considered to be a potential pandemic threat.

Phase 3:
An animal or mixed animal-human virus has caused occasional cases or small clusters of disease, but the virus does not spread easily.

Phase 4:
The new virus can cause sustained outbreaks and is adapting itself to human spread (April 28, 2009).

Phase 5:
The virus has spread into at least two countries and is causing even bigger outbreaks (April 30, 2009)

Phase 6:
Outbreaks in at least two regions of the world; the pandemic is under way.