SCIENTISTS at an Oxford biotech firm have been given further evidence that an experimental vaccine could prevent a global bird flu pandemic.

The DNA vaccine, developed by PowderMed, of Oxford Science Park, has passed safety tests and will now be tried on larger groups of volunteers.

The virus's genetic material DNA is coated with gold particles which are propelled into the skin with helium gas, instead of using a needle.

PowderMed scientists reported in the science journal Vaccine that all 36 volunteers produced an immune response after vaccination, giving protection from the flu strain.

Powdermed's chief executive, Dr Clive Dix, said current stockpiles of bird flu vaccine could only treat 75 million people worldwide, because high doses were needed. But just one kilogram of his company's DNA vaccine could potentially treat 500 million people.

"The advantage of a DNA-based approach is that the vaccines can be manufactured very rapidly and in large quantities, while yielding an immune response at low doses," he said.

PowderMed will now start phase II trials later this year using both annual flu and bird flu strains. A vaccine against bird flu could be ready by 2008, said Dr Dix.

One trial will be in London, with another two in the US.

The powder is produced by copying a gene from the virus and enclosing it in tiny gold particles. The company says its needle-free, virtually painless delivery system requires "minimal medical training, allows self-administration and requires no refrigeration for stockpiling".

Current flu jabs are produced by 50-year-old technology from chicken eggs, with six months of brewing time and an uncertain production process.

Companies working on conventional bird flu vaccines include Novartis, formerly Chiron, which is next door to PowderMed, as well as multinational Sanofi Aventis, which is currently recruiting volunteers for a trial at the Churchill Hospital in Oxford.

So far there have been 224 cases of avian influenza in humans, including 127 fatalities, most of them in Asia. Experts fear it could mutate into a strain easily passed among humans, sparking a global pandemic.