In the post-pandemic period, influenza disease activity will have returned to levels normally seen for seasonal influenza. Pandemic waves can be separated by months and an immediate “at-ease” signal may be premature. Once the level of disease activity drops, a critical communications task will be to balance this information with the possibility of another wave. Previous pandemics have been characterized by waves of activity spread over months. 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. Designation of this phase will indicate that a global pandemic is under way.ĭuring the post-peak period, pandemic disease levels in most countries with adequate surveillance will have dropped below peak observed levels. Phase 6, the pandemic phase, is characterized by community level outbreaks in at least one other country in a different WHO region in addition to the criteria defined in Phase 5. The boundaries and names shown and the designations used on this map do not imply the expression of any opinion whatsoever on the part of the World Health Organization concerning the legal status of any country, territory, city or area of (more.) 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 finalize the organization, communication, and implementation of the planned mitigation measures is short. Phase 5 is characterized by human-to-human spread of the virus into at least two countries in one WHO region ( Figure 4) 23. Phase 4 indicates a significant increase in risk of a pandemic but does not necessarily mean that a pandemic is a forgone conclusion. Any country that suspects or has verified such an event should urgently consult with WHO so that the situation can be jointly assessed and a decision made by the affected country if implementation of a rapid pandemic containment operation is warranted. The ability to cause sustained disease outbreaks in a community marks a significant upwards shift in the risk of a pandemic. Phase 4 is characterized by verified human-to-human transmission of an animal or human-animal influenza reassortant virus able to cause “community-level outbreaks”. However, limited transmission under such restricted circumstances does not indicate that the virus has gained the level of transmissibility among humans necessary to cause a pandemic. Limited human-to-human transmission may occur under some circumstances, for example, when there is close contact between an infected person and an unprotected caregiver. In Phase 3, an animal or human-animal influenza reassortant virus has caused sporadic cases or small clusters of disease in people, but has not resulted in human-to-human transmission sufficient to sustain community-level outbreaks. In Phase 2, an animal influenza virus circulating among domesticated or wild animals is known to have caused infection in humans, and is therefore considered a potential pandemic threat. Even though such viruses might theoretically develop into pandemic viruses, in Phase 1 no viruses circulating among animals have been reported to cause infections in humans. In nature, influenza viruses circulate continuously among animals, especially birds.
Furthermore, periods after the first pandemic wave are elaborated to facilitate post pandemic recovery activities.(see Figure 3)
Phases 1-3 correlate with preparedness, including capacity development and response planning activities, while Phases 4-6 clearly signal the need for response and mitigation efforts. The grouping and description of pandemic phases have been revised to make them easier to understand, more precise, and based upon observable phenomena. In this revision, WHO has retained the use of a six-phased approach for easy incorporation of new recommendations and approaches into existing national preparedness and response plans. The phases are applicable to the entire world and provide a global framework to aid countries in pandemic preparedness and response planning. The WHO pandemic phases were developed in 1999 and revised in 2005.
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