GlaxoSmithKline (GSK) plc announced headline data showing that its H5N1 pandemic flu vaccine achieved a high immune response at a low dose of antigen.

The vaccine, which uses a proprietary adjuvant, enabled over 80 per cent of subjects who received 3.8µg of antigen to demonstrate a strong seroprotective immune response. This level of seroprotection meets or exceeds target criteria set by regulatory agencies for registration of influenza vaccines. Efficacy results at these levels of antigen dosage have also not been reported for any other H5N1 vaccine in development to date, including those using other adjuvants such as alum.

Commenting on the data, JP Garnier, GlaxoSmithKline's chief executive officer, said: "These excellent clinical trial results represent a significant breakthrough in the development of our pandemic flu vaccine. This is the first time such a low dose of H5N1 antigen has been able to stimulate this level of strong immune response.

There is still a lot more work to be done with this programme, but this validation of our approach provides us with the confidence to continue developing the vaccine, including assessment of its ability to offer cross-protection to variants of the H5N1 strain. All being well, we expect to make regulatory filings for the vaccine in the coming months."

The results were based on an interim analysis of a clinical trial conducted in Belgium which involved 400 healthy adults aged 18-60 years of age. The vaccine tested was produced from inactivated H5N1 virus and contained a novel, proprietary adjuvant. An adjuvant is an ingredient which stimulates the immune system and increases response to the vaccine. Trial participants were vaccinated twice during the course of the trial and four different levels of antigen dose were tested, with 3.8µg being the lowest dose assessed.

In this study, immune response was defined as the increase in the number of antibodies an individual produced in response to the vaccine. Levels of antibody protection were established through measurement of hemagglutination inhibition (HI), hemagglutination being the clumping together of red blood cells, which cannot occur when antibodies are present. HI is a standard efficacy measure used in the evaluation of influenza vaccines, and an individual with an HI titer of greater than 40 is considered to be protected, or to have "seroprotection." In this clinical trial, over 80 per cent of subjects, who received 3.8µg of antigen with adjuvant, demonstrated a seroprotective immune response. GSK's adjuvanted investigational pandemic vaccine has not received marketing approval from any regulatory agency.