- Pandemic influenza is different from
avian influenza
- Influenza pandemics are recurring
events
- The world may be on the brink of another
pandemic
- All countries will be affected
- Widespread illness will occur
- Medical supplies will be inadequate
- Large numbers of deaths will occur
- Economic and social disruption will
be great
- Every country must be prepared
- WHO will alert the world when the pandemic
threat increases
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.
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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 40–50 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.
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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.
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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.
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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 world’s 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.
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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.
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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.
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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.
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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 today’s 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.
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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.
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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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(Source: World
Health Organization)
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