WHO Pandemic PhasesThe WHO uses a series of six phases of pandemic alert to inform the world of the seriousness of the pandemic threat and of the need to launch progressively more intensive preparedness activities. Each alert phase coincides with a series of recommended activities by the WHO, the international community, governments, and industry. Changes from one phase to another are triggered by several factors, which include the epidemiological behaviour of the disease and the characteristics of circulating viruses.
The Director-General of the WHO designates global phases, making decisions on when to move from one phase to another.
The WHO scale is based on the real-world development of a pandemic.
Table 1: WHO Pandemic Phases
|Period||Global Phase||Description of Phase|
|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 risk 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 risk of human disease.|
|Pandemic alert period||Phase 3||Human infection(s) with anew subtype but no human-tohuman spread, or at most rare instances of spread to a close contact.|
|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.|
|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 yet be fully transmissible (substantial pandemic risk).|
|Pandemic period||Phase 6||Pandemic: increased and sustained transmission in general population.|
Australian pandemic phasesAustralia uses the same numbering system as WHO to describe each phase; however, the Australian pandemic phases are designed to describe the situation in Australia and to guide Australia’s response. Thus, the Australian and the WHO phase may not always be the same.
The Australian phases describe where the virus is whether in countries overseas (OS) or in Australia (AUS). Different response strategies may be used simultaneously in different parts of Australia, due to variations in the local stage of a pandemic. Having an Australian system means that actions can be taken in Australia before a change of phase is declared by the WHO.
Table 2: Australian Pandemic Phases
|A novel virus with pandemic potential causes severe disease in humans who have had contact with infected animals. There is no effective transmission between humans.
Novel virus has not arrived in Australia.
|Novel virus has not arrived in Australia.
Small cluster of cases in one country overseas.
Large cluster(s) of cases in only one or two countries overseas.
Large cluster(s) of cases in more than two countries overseas.
|Pandemic virus has arrived in Australia causing small number of cases and/or small number of clusters.|
|Pandemic virus is established in Australia and spreading in the community.|
|CONTROL AUS 6c||Customised pandemic vaccine widely available and is beginning to bring the pandemic under control.|
|RECOVER AUS 6d||Pandemic controlled in Australia but further waves may occur if the virus drifts and/or is re-imported into Australia.|
Further information about the Australian pandemic phases can be found in the Australian Health Management Plan for Pandemic Influenza (AHMPPI 2008)