Early clinical trials of a new bird flu vaccine have produced promising results and a phase 3 trial of the cell-based H5N1 flu vaccine is expected to take place early next year.

American drug company Baxter says preliminary results from a phase 1/2 trial indicate its vaccine is safe and final results should be available by the end of 2007.

The company carried out a study with 270 healthy adults healthy adults in Austria and Singapore, who received one of four different concentrations of the vaccine, with some participants also receiving an adjuvant, a substance added to vaccines to improve the immune response.

The experimental vaccine was produced by using new cell-based manufacturing methods which promise the production of much larger quantities of vaccine in a far shorter time.

At present vaccine makers rely on egg-based production methods, which require steady supplies of carefully grown eggs and months of cultivation.

The new method grows the vaccines in labs, in batches of cells called cell cultures.

It seems the vaccine was well tolerated and side effects experienced were similar in occurrence and severity to those reported for seasonal flu vaccines.

Baxter suggests the vaccine could offer cross-protection from other strains of the virus.

The vaccine also induced the production of functional antibodies to H5N1 even at the lowest dose level, which were found on an analysis of serum samples from study subjects, to be active against the Vietnam strain of H5N1 contained in the vaccine as well as strains from Hong Kong and Indonesia.

Although the H5N1 bird flu remains mainly a disease of birds, experts are concerned that should the virus mutate it could easily be transmitted from person to person, with the potential to kill millions of people in a global pandemic.

According to the World Health Organization the virus has claimed at least 148 lives since 2003, mainly in Indonesia, Vietnam, Thailand and China, and resulted in the death, one way or another of millions of birds.

GlaxoSmithKline, Sanofi-Aventis and Novartis are all also working on production of a new vaccine to protect against a pandemic.