pandemic phases

To faciliate planning an effective response to an outbreak of disease with the potential to become a pandemic, the World Health Organization has defined six phases in the development of a pandemic. The stages are illustrated here with reference to influenza. The language is mostly taken verbatim from WHO, The role of National Influenza Centres (NICs) during Interpandemic, Pandemic Alert and Pandemic Periods. Interim Document, May 2007.

Phase	Stage	Characteristics	Main goal of agencies
interpandemic period	1	Risk of human infection with new influenza subtypes considered to be none or low.	Strengthen influenza pandemic preparedness at the global, regional, national and subnational levels.
interpandemic period	2	A circulating animal influenza subtype virus poses a substantial risk of human disease.	Minimize the risk of transmission to humans; detect and report such transmission rapidly if it occurs.
pandemic alert	3	Human infection with a new subtype, but no (or very rare) human-to-human spread.	Ensure rapid characterization of the new virus subtype and early detection, notification and response to cases.
	4	Small cluster(s) with limited and localized human-to-human spread.	Contain the new virus within limited foci or delay spread to gain time to implement preparedness measures, including vaccine development.
	5	Larger cluster(s) but human-to-human spread still localized (substantial pandemic risk).	Maximize efforts to contain or delay spread, to possibly avert a pandemic, and to gain time to implement pandemic response measures.
pandemic	6	Increased and sustained transmission in the general population. • The intensity of activities in a country will depend largely upon whether there are cases in the country. The eventual appearance of cases in all countries is considered virtually inevitable. • Affected countries should follow WHO's recommendations for surveillance. Countries not yet affected should prepare to implement these recommendations rapidly, especially if they have extensive trade/travel links with affected countries.	Minimize the impact of the pandemic.