GlaxoSmithKline (GSK) announces clinical trial data from two new studies, which show, for the first time, that GSK's candidate pre-pandemic split antigen H5N1 vaccine, formulated with GSK's proprietary adjuvant system, provides a substantial level of cross-immunity against a 'drifted' (diverse) strain of H5N1.

It is hoped that the immune response elicited with this vaccine, could help prepare or 'prime' the immune system to rapidly respond against variants of the H5N1 strain and therefore protect the vaccinated population in the event of an H5N1 human pandemic.

In the first study presented at the IX International Symposium on Respiratory Viral Infections (ISRVI), data demonstrated GSK's proprietary adjuvanted candidate pre-pandemic vaccine, containing very low levels of the Vietnam H5N1 antigen (3.8µg), elicits a strong cross-immune neutralizing antibody response in humans against the Indonesian strain of the virus. The neutralizing antibody seroconversion factor at Day 42 was shown to be 25 times greater when the vaccine contained the adjuvant system compared with that observed in the control group immunized with a non-adjuvanted vaccine.

GSK's proprietary adjuvant system also displays powerful antigen-sparing properties as the strong neutralizing response in this study was obtained with only two doses of 3.8µg HA antigen administered 3 weeks apart. This could mean, in effect, that by adding GSK's proprietary adjuvant system vaccine-manufacturing capacity could be increased more than tenfold. The vaccine was shown to have an acceptable safety profile when compared to the control group. As expected, reactogenicity (injection site tenderness) was slightly higher in the vaccine group due to the use of the adjuvant system.

In a second study presented at ISRVI, the data showed that GSK's proprietary adjuvanted pre-pandemic vaccine could protect against two diverse H5N1 flu strains, again at very low levels of antigen. The in vivo data from the pre-clinical studies demonstrated that GSK's adjuvanted vaccine, containing the Vietnam H5N1 strain, was not only able to protect against challenge with the vaccine virus strain but it also provides 96 per cent cross-protection against a lethal challenge with the drifted Indonesia strain of H5N1, giving an additional boost to hopes that pre-pandemic vaccination is a viable strategy for inclusion in pandemic preparedness plans.

Jean Stéphenne, president, GlaxoSmithKline Biologicals, the vaccine division of GSK, commented, "I am extremely encouraged by the new trial data that has been reported today on GSK's candidate pre-pandemic influenza vaccine. The data confirm that our pre-pandemic influenza vaccine has the ability to recognize and kill an H5N1 strain that is different to the one contained in the vaccine. This means that proactive administration of our pre-pandemic vaccine before or just after the start of the pandemic could help to substantially slow down the spread of disease."

Pandemic influenza poses a serious global public health threat with substantial estimated morbidity and mortality. The exact strain that may cause influenza pandemic cannot be accurately predicted. Many experts, however, believe that the avian H5N1 strain, now endemic in many bird species across the world, is the most likely candidate pandemic strain.

"We believe this vaccine will provide governments with a new option to help protect their populations against the threat of a future human influenza pandemic," commented David Stout, president, GSK Pharmaceuticals.