Avian Influenza
Experimental US vaccine blocks bird flu in mice
Feb 3, 2006 - 3:37:37 PM

US researchers have genetically engineered a common cold virus to produce a vaccine they say protects mice from weight loss and death when exposed to the lethal H5N1 bird flu strain, medical journal The Lancet reported Thursday.

The vaccine was produced without using chicken eggs, the conventional growth medium for vaccine production. Eggs could become scarce if the H5N1 infected large swathes of domestic poultry, Mary Hoelscher, the chief researcher on the article, told DPA.

"If you don't have chickens, you don't have eggs," she said.

The antiviral vector the researchers used instead of eggs is a viral tissue culture currently used in making cold and flu immunisations for US military recruits, and is part of the experimental work in developing vaccines against HIV and cancer, Hoelscher said.

Unlike conventional inoculations, which usually contain safe variants of the targeted disease, the vaccine would not contain any form of the H5N1 virus, said Suryaprakash Sambhara of the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia.

Clinical trials on humans are the next step, Hoelscher said.

The bird flu virus, currently transmitted among wild and domestic birds, has prompted the mass culling of geese, ducks, chicken and other domestic fowl throughout Asia as health officials try to stem its spread.

The virus has killed at least 72 people infected directly from birds in the past two years, a 50 percent death rate for those infected. But it has not yet spread from human to human.

Researchers are bracing for a worldwide human epidemic, but are at a loss on how they would produce an effective vaccine for the 1.2 billion people they believe would be threatened in a pandemic.

The research described in the Lancet article took place at CDC and at Purdue University in Indiana.

To make the vaccine, the researchers engineered a common cold virus, called the adenovirus, to produce a protein called "haemugglutinin subtype 5", which they said is a component of the H5N1 bird flu virus.

"The protein stimulates the immune system to make the antibodies" against the H5N1 virus, Sambhara said in a telephone interview.

The advantage of the new vaccine is that it could be mass-produced faster than the conventional egg-derived vaccine, which could take six months and four to six billion fertilised eggs to immunise 1.2 billion people worldwide, the researchers said.

The new vaccine would likely get immediate approval by the US Federal Drug Administration in the event of a pandemic, and could be produced in a few months, Sambhara said.

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