A bird flu vaccine being developed by San Diego-based Vical Incorporated protects mice and ferrets against the feared H5N1 avian influenza virus, the company said on Tuesday.

It may also offer potential as a universal flu vaccine because it targets parts of the virus that all flu strains have, Vical and researchers testing the shot said.

This so-called cross-protection would mean that new vaccines would not have to be formulated every flu season and could provide a chance to stockpile vaccine ahead of a pandemic.

A vaccine that provides cross-protection against more than one strain of flu is important for addressing a pandemic flu threat because it is likely that the H5N1 virus could mutate before it becomes transmissible from human to human, Dr. Richard Webby of St. Jude Children's Research Hospital in Memphis, Tennessee, who tested the vaccine, said in a statement.

Influenza is a virus that makes mistakes easily when replicating itself and thus mutates, or evolves, constantly. For this reason the seasonal flu vaccine is re-formulated every year and people have to get new shots regularly.

The H5N1 avian influenza virus does not yet easily infect people but it has spread in birds across Asia, Europe and parts of Africa. It has infected 205 people and killed 113, but if it evolves the ability to spread easily from human to human it would spark a deadly pandemic.

Current vaccines activate an immune response against the most mutation-prone regions of the virus, which is why they must be changed every year. For this reason, experimental H5N1 vaccines being worked on now are unlikely to provide very good protection against a future pandemic strain.

AVOIDING MUTATIONS

But there are parts of the flu virus that are conserved -- that do not change as strains mutate. Experts have been trying to formulate a vaccine that helps the immune system recognize these proteins.

Vical's vaccine uses three bits of DNA -- the H5 part of the H5N1 avian influenza virus, and genes not so subject to mutation -- the nucleoprotein, or NP, and matrix protein, or

M2.

Mice and ferrets vaccinated with this vaccine and then exposed to H5N1 avian flu virus all survived. Ferrets are considered a good model for human influenza because they become infected with it in a similar way to humans.

Mice vaccinated with a simplified version of the vaccine, which only included NP and M2, were also protected from H5N1, the company reported. This suggests but does not prove the vaccine provides cross-protection against several flu strains, the company said.

Achieving cross-protection is the 'Holy Grail' in flu vaccines, and the current studies provide evidence that such a goal may be feasible using a DNA vaccine targeting conserved influenza virus proteins and formulated with our proprietary Vaxfectin adjuvant, said Vijay Samant, president and chief executive officer of Vical.

Making a bird flu vaccine is big business. The International Federation of Pharmaceutical Manufacturers & Associations says 31 pandemic avian influenza vaccines made by 15 companies in Australia, Austria, Canada, France, Germany, Italy, Japan, the Netherlands, Switzerland, Britain and the United States are in human, or clinical, trials.

One, being developed by Merck and Co., also attempts to be a universal vaccine and focuses on M2.

Research group Datamonitor believes the flu vaccine market could exceed $3 billion by 2010 in the top seven markets alone, against an estimated $1.6 billion worldwide in 2005.

Tennessee Medicine