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Pre-Pandemic Vaccine at the Forefront in Bird Flu Fight |
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By Stephen Leahy*
Scientists
around the globe are working around the clock in search of vaccines
that could improve the human immunological response to a potential
flu pandemic.
TORONTO - Some 17 countries are hard at developing
experiments ultimately aimed at preventing bird flu amongst humans.
So far, avian influenza has killed 120 people. The rapid production
of effective, low-cost vaccines will not prevent a pandemic from
happening, but could sharply reduce its impact.
In 28 clinical trials, scientists are testing different forms of
H5N1, the bird flu virus, to create pre-pandemic vaccines, which
could be a boon at a time when the much-feared mutation that would
facilitate human-to-human transmission has yet to occur.
"An unknown (mutated) virus could show up at any time, and some
of these (bird flu) efforts will help," John Treanor, a virus expert
at the University of Rochester School of Medicine, in New York state,
told Tierramérica.
Over the past year, newer strains of H5N1 have become highly infectious
amongst domestic and wild birds, but not in humans. However, about
120 humans deaths have been linked to H5N1 since 2003 -- all the
result of close contact with infected birds.
The bird flu virus is evolving rapidly, making it very difficult
to predict whether there will be a pandemic or not, says Treanor
Computer models have suggested that within three months a pandemic
virus could reach every continent. Within six to nine months, it
could reach every country. The bird flu could kill as many people
as the "Spanish flu" pandemic of 1918-1919, in which more than 50
million people died, he said.
Once the mutated virus is identified, developing an effective vaccine
against a specific flu strain can take about six months. Immunization
requires that some of the actual virus strain be injected into our
bodies to allow our immune system to build a defense against the
fully-functioning virus.
"Production cannot start before a pandemic strain of flu emerges,"
said Klaus Stohr, head of the World Health Organization's (WHO)
global influenza program.
But efforts to come up with pre-pandemic vaccines are vital. New
reason for hope emerged two weeks ago with evidence that ferrets
immunized with a vaccine based on an H5N1 strain isolated in Hong
Kong in 2003 protected them against a newer variant of the virus.
Pre-pandemic H5N1 vaccines may stimulate a better immune response
than previously believed and merit being stockpiled as initial pandemic
vaccines, according to researchers at St. Jude Children's Research
Hospital in Memphis and the University of Tennessee, located in
the southeastern United States.
Human trials of other H5N1 vaccines are under way elsewhere, including
final phase-three trials by GlaxoSmithKline, involving 5,000 people
from France, Germany, Netherlands, Russian Federation, Spain and
Sweden.
CSL Limited, an Australian pharmaceutical company, is also studying
the safety and effectiveness of its new vaccine in humans this year.
The French pharmaceutical laboratory Sanofi Pasteur has reported
that its vaccine produced a good immune response in two-thirds of
the volunteers tested, and more research is needed. Among the challenges
is reducing the amount of vaccine needed to confer immunity so that
the drug will be available to more people.
Worldwide, vaccine manufacturing has been on the decline for several
years, mainly because there was little profit in providing vaccines
for common childhood illnesses.
Instead, drug companies focus on medications for the aging populations
of industrialized countries. Even seasonal flu vaccines were in
short supply in the United States because low manufacturing capacity.
Currently, the combined output of the world's flu vaccine manufacturers
is about 900 million 15-milligram doses of antigen.
The Sanofi Pasteur H5N1 vaccine requires two 30-mg doses of antigen,
and even if it were fully effective only 225 million could theoretically
be protected.
To counter this shortage, a number of countries and companies are
making new investments. In May, the U.S. government awarded five
contracts totalling more than one billion dollars to develop cell-based
technologies for making flu vaccines.
Traditionally, vaccines are made by injecting the virus into chicken
eggs, where it replicates within the embryo. The method is slow,
requires a lot of space and one or two eggs per dose of vaccine
-- obviously a problem if bird flu decimates chicken populations.
Producing flu vaccines in cell cultures, as is done with polio,
hepatitis A, and chickenpox vaccines, would be faster and a more
flexible approach. And the large pharmaceutical giants are seizing
on this new opportunity, buying and building vaccine manufacturing
facilities.
But few of these facilities are outside of the developed world.
Brazil announced last month that it will invest 13.6 million dollars
to build a new manufacturing plant for seasonal flu vaccine, scheduled
to open in 2007. It will be "a world-class plant, the first in a
developing country," says Jarbas Barbosa da Silva, Jr., undersecretary
of health surveillance for Brazil's Ministry of Health.
In addition, a "pilot unit" will begin production of a pandemic
influenza vaccine based on H5N1 this month, Da Silva said in a statement.
Even if the dreaded bird flu pandemic fails to materialize, the
billions of dollars invested in research and manufacturing will
not be wasted, said virus expert Treanor. The results will help
when some new, unknown virus appears.
* Stephen Leahy is a Tierramérica contributor.
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