Here are the details of the six phases:
No animal influenza virus circulating among animals is reported to cause infection in humans.
Animal influenza virus is known to have caused infection in humans and is therefore a potential pandemic threat.
Animal or human-animal influenza virus causes sporadic cases or clusters of cases in people, but no human-to-human transmission, except in specific circumstances.
Human-to-human transmission of an animal or human-animal influenza virus able to sustain community-level outbreaks.
The ability to cause sustained disease outbreaks in a community marks a significant upwards shift in the risk for a pandemic.
The same virus causes sustained community-level outbreaks in two or more countries in one region.
While most countries will not be affected at this stage, the declaration of Phase 5 is a strong signal that a pandemic is imminent and that the time to finalise the organisation, communication, and implementation of the planned mitigation measures is short.
The virus causes sustained community-level outbreaks in more than one region.
Designation of this phase will indicate that a global pandemic is under way.