Phase 1 |
No animal influenza virus circulating among animals has been reported to cause infection in humans. |
Phase 2 |
An animal influenza virus circulating in domesticated or wild animals is known to have caused infection in humans and is therefore considered a specific potential pandemic threat. |
Phase 3 |
An animal or human-animal influenza reassortant virus has caused sporadic cases or small clusters of disease in people, but has not resulted in human-to-human transmission sufficient to sustain community-level outbreaks. |
Phase 4 |
Human-to-human transmission (H2H) of an animal or human-animal influenza reassortant virus able to sustain community-level outbreaks has been verified. |
Phase 5 |
The same identified virus has caused sustained community level outbreaks in two or more countries in one WHO region. |
Phase 6 |
In addition to the criteria defined in Phase 5, the same virus has caused sustained community level outbreaks in at least one other country in another WHO region. |
Post-peak period |
Levels of pandemic influenza in most countries with adequate surveillance have dropped below peak levels. |
Possible
new wave |
Level of pandemic influenza activity in most countries with adequate surveillance rising again. |
Post-
pandemic period |
Levels of influenza activity have returned to the levels seen for seasonal influenza in most countries with adequate surveillance |
