The Pandemic Alert Scale from the WHO

The World Health Organization (WHO) says that swine flu is moving closer to Phase 5 of the pandemic alert scale. This begs the question, what the heck is the pandemic alert scale?

Developed in 1999, the WHO Global Influenza Preparedness Plan breaks potential (and actual) influenza pandemics into six phases.

Phase 1:
No new strains of human influenza

Phase 2:
New animal strain not shown to affect humans but has potential

Phase 3:
New animal subtype of influenza now infecting humans. No human to human spread.

Phase 4:
Small clusters with limited human to human transmission, highly localized.

Phase 5:
Large clusters of human to human spread but still localized. Suggests virus is becoming increasingly better adapted to humans. May not be fully transmissible but has substantial pandemic risk.

Phase 6:
Pandemic status. Increased and sustained transmission in general population.

The WHO uses these phases to determine what plan is best to try and contain the outbreak. The information on the plans themselves is very vague and is likely classified.

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