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US using live viruses to create nasal vaccines against bird flu
(AP)
Updated: 2005-12-16 09:18
In an isolation ward of a Baltimore hospital, up to 30 volunteers will
participate in a bold experiment: A vaccine made with a live version of the most
notorious bird flu will be sprayed into their noses.
First, scientists are dripping that vaccine into the tiny nostrils of mice.
It doesn't appear harmful _ researchers have weakened and genetically altered
the virus so that no one should get sick or spread germs _ and it protects the
animals enough to try in people.
This is essentially FluMist for bird flu, and the hope is that, in the event
of a flu pandemic, immunizing people through their noses could provide faster,
more effective protection than the troublesome shots _ made with a killed virus
_ the nation now is struggling to produce.
And if it works, this new vaccine frontier may not just protect against the
bird flu strain, called H5N1, considered today's top health threat. It offers
the potential for rapid, off-the-shelf protection against whatever novel
variation of the constantly evolving influenza virus shows up next _ through a
library of live-virus nasal sprays that the National Institutes of Health plans
to freeze.
"It's high-risk, high-reward" research, said Dr. Brian Murphy, who heads the
NIH laboratory where Dr. Kanta Subbarao is brewing the nasal sprays _ including
one for a different bird-flu strain that appeared safe during the first crucial
human testing last summer.
"It might fail, but if it's successful, it might prevent hundreds of
thousands of cases" of the next killer flu, Murphy said.
FluMist is the nation's nasal-spray vaccine that prevents regular winter flu.
Developed largely through Murphy's lab, it's the only flu vaccine made with live
but weakened influenza viruses.
The new project, a collaboration with FluMist manufacturer MedImmune Inc.,
piggybacks cutting-edge genetics technology onto that vaccine to create a line
of FluMist-like sprays against different bird flus.
"That is a great, great idea," said Dr. John Treanor of the University of
Rochester, among the flu specialists closely watching the project.
Regular winter flu shots are made with killed influenza viruses, and the
government is stockpiling experimental bird-flu vaccine made the same way. But
those bird-flu shots don't work as well as hoped. They require an incredibly
high dose, delivered in two separate injections, to spark a protective immune
response in people.
"In theory, a live-virus vaccine might actually work better. We don't know
that because we've never tried one before," Treanor said.
Influenza is like a magician, constantly changing its clothes to avoid
detection, thus making it difficult to develop effective vaccines.
Studding the virus' surface are two proteins called hemagglutinin _ the H in
H5N1 _ and neuraminidase, the "N". They act as a wardrobe: There are 16 known
hemagglutinin versions, and nine neuraminidases.
They're also what triggers the immune system to mount an attack, particularly
hemagglutinin, the protein the body aims for when it makes flu-fighting
antibodies.
When people catch the flu, they usually get H1 or H3 flu strains, which their
bodies can recognize because variations have circulated among humans for
decades.
Occasionally, genetically unique strains emerge. Until 1997, H5 strains had
never been seen outside of birds. The virus essentially put on a coat that human
immune systems didn't recognize. The result: Since 2003, a particularly strong
H5N1 strain has infected more than 130 people in Asia, killing at least 70.
H9 and H7 strains also recently have jumped from birds to people, although so
far they haven't been nearly as dangerous.
Researchers hope to create at least one live-virus nasal spray for each "H"
subtype, a project costing about $16 million (euro13.4 million) of the NIH's
annual $67 million (euro56.2 million) budget for flu vaccine research.
"The hemagglutinin is the major protective antigen, so that is what we're
focusing on," explained Subbarao, a molecular geneticist who heads the project.
First on her list are the riskiest known bird flus: H5N1, with human tests
planned for April. H9N2, which recently underwent the first round of human
testing in an isolation ward at Johns Hopkins Bayview Medical Center. Then an H7
strain, followed by an H6 strain believed to share genes with the H5N1.
"By no means are we confident we're picking the right strain" to make first,
because flu mutates so easily, Subbarao cautioned.
She chooses vaccine strains from those that U.S. scientists who are
monitoring influenza in Asia cull from ducks, chickens and geese, and ship home
for research.
Subbarao must customize those strains for safe vaccination: First, using a
new technique called reverse genetics, she selects genes for bird-flu H and N
antigens and removes genetic segments that make them dangerous. Then she adds
the remaining gene segments to the regular weakened FluMist virus.
Stocks of the custom virus are grown in fertilized chicken eggs. Each is then
carefully cracked by hand to drain out virus-loaded liquid that in turn is
purified and put into a nasal spray.
In a high-security section of the lab, Subbarao dons a biohazard suit and
exposes vaccinated mice to various bird flu strains.
Then it's time for human testing _ in a hospital isolation ward just in case
the weakened virus could infect someone.
It shouldn't, because "those problems don't exist in FluMist," said Murphy,
citing studies of regular FluMist in day-care centers where youngsters routinely
pass viruses back and forth.
Some studies have found that people can shed virus shortly after receiving
regular FluMist. But, "to spread infection, you'd need much more (virus) than
replicates in the nose," he said.
Hopkins researchers gave the first of Subbarao's vaccine candidates _ the
H9N2 spray _ to 30 volunteers last summer. To be sure they couldn't spread the
virus by coughing or sneezing, the volunteers underwent daily tests of their
noses and throats.
The vaccine appeared safe. Scientists now are analyzing whether it also
spurred production of flu-fighting antibodies, a sign that people would be
protected if they encountered the H9N2 strain. Subbarao expects results by
February.
In April, pending final Food and Drug Administration permission, Subbarao
will put an H5N1 spray to a similar test.
Here's the catch: Each flu strain has subtypes. An Indonesian version of
H5N1, for example, was recently discovered that differs from a Vietnamese strain
on which Subbarao's nasal spray _ and the government's stockpiled shots _ are
based. She's now testing whether her vaccine protects mice against that new
Indonesian strain.
If a novel flu strain begins spreading among people, how will Subbarao tell
if her stored nasal vaccines are a good match to fight it?
NIH also will store blood samples from the people who test those sprays. Say
a new H9 strain sparks an outbreak. That virus will be tested against those
blood samples, and NIH could predict within a day which spray candidates work.
If one does, the government could order doses manufactured from that frozen
stock; if none do, scientists would have to try to brew a new vaccine.
How quickly doses could be manufactured is a different issue. All influenza
vaccines, shots or spray, currently are brewed in chicken eggs, a time-consuming
process that other research is seeking to improve.
"These are research projects," Murphy stresses _ the nasal-spray concept
could fail.
But he's optimistic. Live-virus vaccines, he maintains, are better immune
stimulators.
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