Scientists have produced a vaccine against deadly H5N1 strains of bird flu that has protected mice, using a genetic engineering technique that can be easily scaled up for stockpiling to prepare for a pandemic.Dr Suryaprakash Sambhara, of the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, said it can be made much more quickly than conventional vaccines and enough doses could be produced to protect people at risk.
It is also effective against newer strains of flu and does not need an adjuvant, or additive, to boost the immune system response.
"This vaccine can protect humans against newer viruses," Sambhara said in an interview on Thursday.
"Our goal is to move it forward to Phase 1 clinical trials."
Developing a vaccine that can be easily and quickly produced is the best hope of preventing millions of deaths from pandemic flu. Global health officials fear the H5N1 avian flu that has spread from Asia could mutate into a strain that could pass easily from person to person.
So far the virus that has killed at least 85 people since late 2003 has not shown it is highly infectious in humans.
Feasible strategy
Current vaccines, which can take up to 6 months to produce, are made in fertilized chicken eggs. Scientists estimate that 4 billion eggs would be needed to produce enough pandemic vaccine for the up to 2 billion people worldwide who would be at high risk.
Egg-based vaccines are also not useful for stockpiling because a vaccine would have to be specific to the pandemic strain.
Sambhara, Dr Suresh Mittal of Purdue University in Indiana and their colleagues genetically engineered an adenovirus, or common cold virus, to produce a protein call haemugglutnin subtype 5 (H5HA), which is a component of the H5N1 virus.
"This H5 adenovirus vaccine is an egg-independent and adjuvant-independent strategy," said Sambhara.
The scientists injected one group of mice with the new vaccine and another with a saline solution before infecting the animals with H5N1 viruses isolated from people in 2003 and 2004.
The scientists, whose findings are reported online by The Lancet medical journal, said although the vaccinated mice had low or no antibodies they did not lose weight or die.
Antibodies are immune system proteins that neutralize the virus. The H5 adenovirus vaccine generated immune system cells called T cells in the mice that attacked the strains of recent H5N1 avian influenza.
"It not only induces antibodies, it also induces T cells response," said Sambhara.
He added that many million doses of the vaccine can be made with existing technology.
"This approach is a feasible vaccine strategy against existing and newly emerging viruses of highly pathogenic avian influenza to prepare against a pandemic," the scientists said in the journal.
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