- 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 [pdf 113kb] 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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