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Pandemic Influenza: Ten Things You Need To Know
Oct. 17, 2005 - The following information was prepared by the World Health Organization in response to
the heightened interest in the avian (bird) flu that many see is the
threat of a worldwide pandemic. This information was current on October
14, 2005. They also have released "Avian Influenza Frequently Asked Questions,"
which you can read - click here.
1. Pandemic influenza is different from avian
influenza.
Avian influenza refers to a large group of
different influenza viruses that primarily affect birds. On rare
occasions, these bird viruses can infect other species, including pigs
and humans. The vast majority of avian influenza viruses do not infect
humans. An influenza pandemic happens when a new subtype emerges that
has not previously circulated in humans.
For this reason, avian H5N1 is a strain with
pandemic potential, since it might ultimately adapt into a strain that
is contagious among humans. Once this adaptation occurs, it will no
longer be a bird virus--it will be a human influenza virus. Influenza
pandemics are caused by new influenza viruses that have adapted to
humans.
2. Influenza pandemics are recurring events.
An influenza pandemic is a rare but recurrent
event. Three pandemics occurred in the previous century: Spanish
influenza in 1918, Asian influenza in 1957, and Hong Kong influenza
in 1968. The 1918 pandemic killed an estimated 4050 million people
worldwide. That pandemic, which was exceptional, is considered one of
the deadliest disease events in human history. Subsequent pandemics were
much milder, with an estimated 2 million deaths in 1957 and 1 million
deaths in 1968.
A pandemic occurs when a new influenza virus
emerges and starts spreading as easily as normal influenza by coughing
and sneezing. Because the virus is new, the human immune system will
have no pre-existing immunity. This makes it likely that people who
contract pandemic influenza will experience more serious disease than
that caused by normal influenza.
3. The world may be on the brink of another
pandemic.
Health experts have been monitoring a new and
extremely severe influenza virus the H5N1 strain for almost eight
years. The H5N1 strain first infected humans in Hong Kong in 1997,
causing 18 cases, including six deaths. Since mid-2003, this virus has
caused the largest and most severe outbreaks in poultry on record. In
December 2003, infections in people exposed to sick birds were
identified.
Since then, over 100 human cases have been
laboratory confirmed in four Asian countries (Cambodia, Indonesia,
Thailand, and Viet Nam), and more than half of these people have died.
Most cases have occurred in previously healthy children and young
adults. Fortunately, the virus does not jump easily from birds to humans
or spread readily and sustainably among humans. Should H5N1 evolve to a
form as contagious as normal influenza, a pandemic could begin.
4. All countries will be affected.
Once a fully contagious virus emerges, its global
spread is considered inevitable. Countries might, through measures such
as border closures and travel restrictions, delay arrival of the virus,
but cannot stop it. The pandemics of the previous century encircled the
globe in 6 to 9 months, even when most international travel was by ship.
Given the speed and volume of international air travel today, the virus
could spread more rapidly, possibly reaching all continents in less than
3 months.
5. Widespread illness will occur.
Because most people will have no immunity to the
pandemic virus, infection and illness rates are expected to be higher
than during seasonal epidemics of normal influenza. Current projections
for the next pandemic estimate that a substantial percentage of the
worlds population will require some form of medical care. Few countries
have the staff, facilities, equipment, and hospital beds needed to cope
with large numbers of people who suddenly fall ill.
6. Medical supplies will be inadequate.
Supplies of vaccines and antiviral drugs the two
most important medical interventions for reducing illness and deaths
during a pandemic will be inadequate in all countries at the start of
a pandemic and for many months thereafter. Inadequate supplies of
vaccines are of particular concern, as vaccines are considered the first
line of defence for protecting populations. On present trends, many
developing countries will have no access to vaccines throughout the
duration of a pandemic.
7. Large numbers of deaths will occur.
Historically, the number of deaths during a
pandemic has varied greatly. Death rates are largely determined by four
factors: the number of people who become infected, the virulence of the
virus, the underlying characteristics and vulnerability of affected
populations, and the effectiveness of preventive measures. Accurate
predictions of mortality cannot be made before the pandemic virus
emerges and begins to spread. All estimates of the number of deaths are
purely speculative.
WHO has used a relatively conservative estimate
from 2 million to 7.4 million deaths because it provides a useful and
plausible planning target. This estimate is based on the comparatively
mild 1957 pandemic. Estimates based on a more virulent virus, closer to
the one seen in 1918, have been made and are much higher. However, the
1918 pandemic was considered exceptional.
8. Economic and social disruption will be great.
High rates of illness and worker absenteeism are
expected, and these will contribute to social and economic disruption.
Past pandemics have spread globally in two and sometimes three waves.
Not all parts of the world or of a single country are expected to be
severely affected at the same time. Social and economic disruptions
could be temporary, but may be amplified in todays closely interrelated
and interdependent systems of trade and commerce. Social disruption may
be greatest when rates of absenteeism impair essential services, such as
power, transportation, and communications.
9. Every country must be prepared.
WHO has issued a series of
recommended strategic actions for responding to the influenza
pandemic threat. The actions are designed to provide different layers of
defence that reflect the complexity of the evolving situation.
Recommended actions are different for the present phase of pandemic
alert, the emergence of a pandemic virus, and the declaration of a
pandemic and its subsequent international spread.
10. WHO will alert the world when the pandemic
threat increases.
WHO works closely with ministries of health and
various public health organizations to support countries' surveillance
of circulating influenza strains. A sensitive surveillance system that
can detect emerging influenza strains is essential for the rapid
detection of a pandemic virus.
Six distinct phases have been defined to facilitate
pandemic preparedness planning, with roles defined for governments,
industry, and WHO. The present situation is categorized as phase 3: a
virus new to humans is causing infections, but does not spread easily
from one person to another.
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