August 03, 2005
Computer Model Could Help Prevent Flu Pandemic
Close disease surveillance and targeted use of anti-viral drugs
could be enough to keep a small outbreak of avian flu from becoming the
first influenza pandemic in 36 years, according to a new computer model
designed to prepare at-risk nations for a pandemic that could affect
millions worldwide.
The best weapon is containment, said Neil Ferguson, a Howard Hughes
Medical Institute international research scholar and professor of
mathematical biology at Imperial College London. Ferguson headed a
study whose findings are being published online by the journal
Nature on August 3, 2005.
“It's an enormous undertaking that will require cooperation among governments on a large scale.”
Neil Ferguson
The last influenza pandemic occurred in 1968, caused by a virus that
first appeared in Hong Kong. By September of that year, the so-called
Hong Kong flu had arrived in the United States, and by March 1969, an
estimated 675,000 Americans had gotten sick and nearly 34,000 had died.
Scientists say that an outbreak of avian or bird flu, the most likely
candidate for an influenza pandemic, could be much worse now because
humans have no immunity to it, and in today's world, infected persons
can travel almost anywhere within 48 hours, potentially transmitting
the virus to every individual they encounter along the way.
The first human cases of avian flu were reported in Hong Kong in
1997, where hundreds were infected and six people died. In that
outbreak, humans contracted the virus from infected poultry. But
viruses tend to mutate, and scientists fear the virus that causes avian
flu—H5N1 influenza A virus—might alter its molecular
structure and become transmissible from human to human. There is no
vaccine for H5N1, and even if there were, it would be difficult to
develop and distribute enough vaccine for all those at risk around the
world.
In the scientists' computer model, a single resident of a rural
village in Thailand was infected with a mutated H5N1 virus capable of
human-to-human transmission. Scientists say that an avian flu pandemic
would likely begin in southeast Asia, and the researchers chose
Thailand because the type of national data they needed was easily
accessible. Using information on past influenza pandemics, they
calculated the number of secondary cases that would occur from the
original infected individual, the normal incubation period of the
illness, and the speed with which the pandemic would spread.
They then added demographic information such as regional and
national population size and age; numbers of households, schools and
large companies; and distances that people travel to work and school.
This gave them a map of how the virus might spread.
It took the research team a year to collect the data for their
model. “You need to collect as much data as possible ahead of
time for this sort of modeling,” Ferguson said. Few countries in
the region publish information about locations of schools and major
companies, how far people travel to get to school or work, and use of
public transportation, and even where they do, the data needs to be
collated and analysed before scientists can use it, he explained.
After crunching the data, the researchers used the model to test a
number of strategies to limit the spread of the influenza virus. Since
no avian flu vaccine currently exists, they proposed anti-viral
prophylaxis as a way to reduce the risk of infection among people
surrounding the initial cluster of flu victims. Prophylaxis involves
treating healthy people with drugs to protect them against infection.
It is like a temporary vaccine.
“To be effective,” Ferguson said, “you really must
use a combination of strategies. No single one would successfully
prevent an epidemic.”
“To apply this model in real-time during an outbreak, you'd
use it to track the epidemic, to predict trends, to see if what you're
doing is working,” the scientist added. “Models can be used
ahead of time to find out what needs to be done logistically to contain
the spread of the virus or mitigate its effects”.
The first step in preventing a pandemic, Ferguson said, is for
doctors to quickly recognize that the virus is something unusual and
notify government health officials. Then, infected patients should be
isolated from other populations. Steps such as closing schools and work
places and limiting access to gathering spots should be taken to
increase “social distance”—reducing opportunities for
infected people to transmit the virus to others. Finally, Ferguson and
his colleagues recommend that public health officials treat the 20,000
people closest to the outbreak with anti-viral drugs. It might take a
stockpile of as many as 3 million doses of anti-viral treatments to
eliminate an outbreak, the scientist said.
The effort and resources required to implement these types of
policies are considerable, Ferguson noted. In addition to a drug
stockpile, surveillance needs to be improved, and public health teams
who would implement a containment strategy need to be trained.
During a new pandemic outbreak, the model would have to be applied
within a few days or weeks to be useful in the control effort.
“It's an enormous undertaking that will require cooperation among
governments on a large scale. But that's what necessary for this to
become more than just a computer model, but an actual
possibility,” Ferguson said.
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Cindy Fox Aisen
