GlaxoSmithKline reports advance in H5N1 flu vaccine program

By E. Janene Geiss

Philadelphia, July 26 - GlaxoSmithKline plc said Wednesday that headline data shows 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 more than 80% of subjects who received 3.8 micrograms of antigen to demonstrate a strong seroprotective immune response, according to a company news release.

This level of seroprotection meets or exceeds target criteria set by regulatory agencies for registration of influenza vaccines, officials said.

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.

"This is the first time such a low dose of H5N1 antigen has been able to stimulate this level of strong immune response," JP Garnier, GlaxoSmithKline's chief executive officer, said in the release.

If the vaccine continues to advance, the company said it expects to make regulatory filings in the coming months.

The results were based on an interim analysis of a clinical trial conducted in Belgium that involved 400 healthy adults between the ages of 18 to 60.

The vaccine tested was produced from inactivated H5N1 virus and contained a novel, proprietary adjuvant.

An adjuvant is an ingredient that 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 3.8 micrograms 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, more than 80% of subjects who received 3.8 micrograms of antigen with adjuvant demonstrated a seroprotective immune response, officials said.

GlaxoSmithKline's adjuvanted investigational pandemic vaccine has not received marketing approval from any regulatory agency.

GlaxoSmithKline is a London pharmaceutical and health care company.

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