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WHO six-phase guide to pandemic alerts

April 30, 2009

PHASE 1
No animal influenza virus circulating among animals is reported to cause infection in humans.

PHASE 2
Animal influenza virus is known to have caused infection in humans and is therefore a potential pandemic threat

PHASE 3
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

PHASE 4
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.

PHASE 5
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.

PHASE 6
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.

POST PEAK

Pandemic disease levels in most countries with adequate surveillance will have dropped below peak observed levels.

The post-peak period signifies that pandemic activity appears to be decreasing; however, it is uncertain if additional waves will occur and countries will need to be prepared for a second wave.

POST PANDEMIC

Influenza disease activity will have returned to levels normally seen for seasonal influenza.

Swine flu interactive graphic map.

Up to 159 people are thought to have died from swine flu in Mexico. Legend: Black mask - deaths; Red mask - confirmed cases; Yellow mask - suspected cases

Up to 159 people are thought to have died from swine flu in Mexico. Legend: Black mask - deaths; Red mask - confirmed cases; Yellow mask - suspected cases

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