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 4.
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.
Fuente
Organización Mundial de la Salud
http://www.who.int
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