A candidate vaccine against the H5N1 strain of avian influenza, developed by French drugmaker Sanofi-Aventis, has been found to be safe and effective in a Phase I trial published yesterday in The Lancet.

The vaccine, developed by Sanofi Pasteur, is based on a modified strain of the virus. Two doses of the candidate produced protective antibodies in the trial, which involved 300 healthy volunteers.

The authors of the study said the regimen of two 30mcg doses was safe - with only a few cases of adverse reactions – and achieved an antibody response “consistent with European regulatory requirements for licensure of seasonal influenza vaccine.”

However, they cautioned that the actual level of antibodies that would provide protection against H5N1 is currently unknown.

The study involved several formulations of the vaccine, half of which were adjuvanted with alum, with the 30mcg version using an adjuvant performing the best with a 67% seroconversion rate. But there were encouraging responses with lower doses of the vaccine, which could mean that currently limited stocks of the antigen could be stretched further in the event of an H5N1 flu pandemic.

A study of a similar, unadjuvanted candidate H5N1 vaccine produced by Sanofi Pasteur in the USA that was published in the New England Journal of Medicine in March required two 90mcg doses to generate a significant immune response in about 50% of trial participants, leading to fears that antigen stocks laid in by the US government would only provide a quarter of the number of doses initially envisaged.

Lancet editor Richard Horton said the results were particularly encouraging and mean that it should be possible of developing an effective vaccine over the next 12 to 18 months.

A number of other companies are working on the development of pandemic flu vaccines, in most cases based on the H5N1 strain, including GlaxoSmithKline, Chiron, Akzo Nobel, MedImmune and Baxter International.

All told, 31 vaccines against bird flu are currently being tested in clinical trials, with 22 targetting the H5N1 strain which has infected 186 people in eight countries and killed 105, according to the latest World Health Organisation figures. Eight vaccines will have undergone Phase II trials by the end of 2006.