Suryaprakash Sambhara, of the Centres 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," Dr 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 a flu pandemic.

Global health officials fear that 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, which has killed at least 85 people since late 2003, has not shown that it is highly infectious in humans. 
   
Current vaccines, which can take up to six months to produce, are made in fertilised chicken eggs.

Scientists estimate that four billion eggs would be needed to produce enough vaccine for the up to two billion people worldwide who would be at high risk in a flu pandemic.

Egg-based vaccines are also not useful for stockpiling because a vaccine would have to be specific to the pandemic strain. 

T cells
   
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 haemagglutinin subtype 5 (H5HA), which is a component of the H5N1 virus.
   
"This H5 adenovirus vaccine is an egg-independent and adjuvant-independent strategy," Sambhara said. 
   

"This vaccine can protect humans against newer viruses"

Dr Suryaprakash Sambhara, of the Centres for Disease Control and Prevention (CDC) in Atlanta, Georgia,

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 neutralise 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," Sambhara said.
   
He said 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.