Pandemic planning

New WHO pandemic phases

PHASES AS PUBLISHED BY WHO IN 1999	NEW PANDEMIC PHASES	ADDITIONAL NATIONAL SUBDIVISIONS OF NEW PHASES
Interpandemic period Phase 0	Interpandemic period Phase 1. No new influenza virus subtypes have been detected in humans. An influenza virus subtype that has caused human infection may be present in animals. If present in animals, the riska of human infection or disease is considered to be low.
	Phase 2. No new influenza virus subtypes have been detected in humans. However, a circulating animal influenza virus subtype poses a substantial riska of human disease.	Affected or extensive travel/trade links with affected country.
		Not affected.
Phase 0. Preparedness level 1: human case.	Pandemic alert period Phase 3. Human infection(s) with a new subtype, but no human-to-human spread, or at most rare instances of spread to a close contact.	Affected or extensive travel/trade links with affected country.
		Not affected.
Phase 0. Preparedness level 2: limited human transmission.	Phase 4. Small cluster(s) with limited human-to-human transmission but spread is highly localized, suggesting that the virus is not well adapted to humans.b	Affected or extensive travel/trade links with affected country.
		Not affected.
Phase 0. Preparedness level 3: spread in general population.	Phase 5. Larger cluster(s) but human-to-human spread still localized, suggesting that the virus is becoming increasingly better adapted to humans, but may not be fully transmissible (substantial pandemic risk).b	Affected or extensive travel/trade links with affected country.
		Not affected.
Pandemic period Phase 1. Multiple countries	Pandemic period Phase 6. Pandemic phase: increased and sustained transmission in general population.b	Not yet affected.
Phase 2. Multiple regions		Affected or extensive travel/trade links with affected country.
Phase 3. Subsiding in initially affected countries but not in other countries		Subsided.
Phase 4. Next wave		Next wave.
Postpandemic period Phase 5. Return to phase 0	Postpandemic period Return to interpandemic period.	Return to interpandemic period.

^a The distinction between phase 1 and phase 2 is based on the risk of human infection or disease resulting from circulating strains in animals. The distinction would be based on various factors and their relative importance according to current scientific knowledge. Factors may include: pathogenicity in animals and humans; occurrence in domesticated animals and livestock or only in wildlife; whether the virus is enzootic or epizootic, geographically localized or widespread; other information from the viral genome; and/or other scientific information.

^b The distinction between phase 3 , phase 4 and phase 5 is based on an assessment of the risk of a pandemic. Various factors and their relative importance according to current scientific knowledge may be considered. Factors may include: rate of transmission; geographical location and spread; severity of illness; presence of genes from human strains (if derived from an animal strain); other information from the viral genome; and/or other scientific information.

(Source: http://www.who.int/csr/resources/publications/influenza/GIP_2005_5Eweb.pdf)

Last updated: 12 December 2005