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http://www.who.int/csr/disease/avian_influenza/phase/en/index.html
Current WHO phase of pandemic alert
Current phase of alert in the WHO global influenza preparedness plan
Pandemic preparedness
In the 2009 revision of the phase descriptions, 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
grouping and description of pandemic phases have been revised to make them
easier to understand, more precise, and based upon observable phenomena.
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. Furthermore, periods after the first
pandemic wave are elaborated to facilitate post pandemic recovery activities.
The current WHO phase of pandemic alert is 5.
In nature, influenza viruses circulate continuously among animals, especially
birds. 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 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.
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. 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. 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.
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.” The ability to cause sustained disease outbreaks in a community
marks a significant upwards shift in the risk for a pandemic. 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. Phase 4 indicates a significant increase in risk of a pandemic
but does not necessarily mean that a pandemic is a forgone conclusion.
Phase 5 is characterized by human-to-human spread of the virus into at least
two countries in one WHO region. 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 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. Designation of this phase will indicate that a
global pandemic is under way.
During the post-peak period, pandemic disease levels in most countries with
adequate surveillance will have dropped below peak observed levels. 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.
Previous pandemics have been characterized by waves of activity spread over
months. Once the level of disease activity drops, a critical communications
task will be to balance this information with the possibility of another
wave. Pandemic waves can be separated by months and an immediate “at-ease”
signal may be premature.
In the post-pandemic period, influenza disease activity will have returned to
levels normally seen for seasonal influenza. It is expected that the pandemic
virus will behave as a seasonal influenza A virus. At this stage, it is
important to maintain surveillance and update pandemic preparedness and
response plans accordingly. An intensive phase of recovery and evaluation may
be required.
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