WASHINGTON (Reuters) - An experimental flu vaccine that blasts tiny particles into the skin instead of using a needle appears to be safe in people, biotech firm PowderMed Ltd. said on Wednesday.

The British-based company said it would move into bigger tests of its vaccine, which uses DNA from the flu virus to stimulate immunity.

Writing in the journal Vaccine, PowderMed scientists said the vaccine stimulated an immune response in all 36 volunteers.

Based on these results, PowderMed will start phase II studies using both annual and bird flu strains later this year. A finished product would still be years away.

"Recent years have seen a number of new influenza vaccine approaches tested in animal model systems and in the clinic. However, this study is the first successful demonstration of immunogenicity of an influenza DNA vaccine in humans," said Dr. Hansi Dean, formerly with PowderMed and now with the International AIDS Vaccine Initiative.

"DNA vaccines have the potential to significantly limit the burden of disease. The advantage of a DNA-based approach is that the vaccines can be manufactured very rapidly and in large quantities, while yielding an efficacious immune response at low doses," added Dr. Clive Dix, chief executive officer of PowderMed.

PowderMed´s vaccine is produced by copying a gene from the virus -- either the circulating influenza virus or the H5N1 avian flu virus -- and enclosing it in tiny gold particles.

It is delivered using an injector powered by concentrated helium gas, which pushes the particles into the skin. The privately held firm is counting on some studies that suggest vaccines delivered right under the skin may produce better immunity than injected vaccines.

And the company said the vaccine is stable and does not need to be refrigerated, or even administered by medical professionals, as are current vaccines.

Several companies make influenza vaccines and are also working on H5N1 vaccines. They include Sanofi Aventis SA, Chiron Corp, GlaxoSmithKline Plc, Acambis Plc and Dutch biotech company Crucell NV.

Current influenza vaccines are based on 50-year-old technology that requires live chicken eggs, six months of brewing time and an uncertain production process.

Governments want to encourage companies that can produce cleaner vaccines in less time. They hope an influenza pandemic does not come in the meantime, but fear the H5N1 virus could evolve into a pandemic strain of flu at any time.