Geoscience Reference
In-Depth Information
he WHO phases measure the
transmissibility
of a virus, not the
severity
of
a resultant pandemic. This is a key difference because many pandemic plans are
based on severity of the illness. Although the WHO might measure a pandemic as
being at a high level (e.g., levels “5” or “6”), the WHO is indicating that triggers
show the virus to be transmissible at the levels indicated in the WHO phase chart
(e.g., “widespread human infection” for levels 5 and 6), not that resulting illnesses
are necessarily severe (although that might also be the case). The WHO recently
made clarifications to their phase structure,
*
but the phases themselves still relate
to the transmissibility of the virus.
With respect to severity, at this writing, the WHO has not yet developed a sys-
tem for measuring this characteristic of a pandemic. “Severity” refers to not only the
degree of virulence of a virus (e.g., number of severe illnesses and deaths, contagious-
ness of the virus, age distribution of cases, prevalence of chronic health problems
and malnutrition of the population, viral mutations, number of waves of illness, and
quality of health services) but also the overall socioeconomic impact of the outbreak.
11
Although the WHO may be developing such a severity index, HHS already
has one in place. Based on hurricane classifications, this system is shown in Figure
17.4.
12
The HHS Pandemic Severity Index is part of the agency's guidance on com-
munity interventions for combating a pandemic. The index is based on case fatal-
ity rates (CFR), with a CFR of 2% or greater signaling the most severe pandemic
(Category 5). The earlier described outbreaks of 1957 and 1968 would be rated as
Category 2 events, with CFRs between 0.1% and 0.5%.
12
Note that there is poten-
tial for public confusion when using this index in combination with the WHO
pandemic phases, which may have led to WHO's delay in presenting a similar
index. HHS has presented numerous cross-references between their index and
WHO's and has included characteristics and interventions for each severity level.
The WHO and HHS tools depend on faithful and timely reporting of the rel-
evant triggers. During the 2009 and 2010 Swine Flu pandemic, it was reassuring
to see that no apparent cover-up existed on the part of any nation with respect to
reporting the illness (as some had believed might have been the case for report-
ing the 2002 and 2003 SARS event). However, there was concern not only that
some time had passed—perhaps three weeks or more
13
—between the first cases in
Mexico and the first WHO warnings, but also that some time had passed before
the Centers for Disease Control and Prevention (CDC) identified the novel variant
*
The World Health Organization (WHO), http://www.who.int/csr/disease/avian_influenza/
phase/en/index.html. Of note, “In the 2009 revision of the phase descriptions, WHO has
retained the use of a six-phase approach for easy incorporation of new recommendations and
approaches into existing national preparedness and response plans. The grouping and descrip-
tion of pandemic phases have been revised to make them easier to understand, more precise,
and based on observable phenomena. Phases 1-3 correlate with preparedness, including capac-
ity 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 postpandemic recovery activities.”
