GSK announced that the US Department of Health and Human Services (HHS) has placed initial orders for A (H1N1) influenza vaccine antigen and the company's proprietary adjuvant system, AS03, to support its pandemic influenza preparation efforts.

GSK manufactures both a traditional vaccine antigen, which will be made from the recently isolated A (H1N1) influenza strain, as well as an adjuvant system. An adjuvant system can be added to the antigen at time of administration.

GSK expects to fill the US adjuvant order within the next few months. The first doses of the vaccine antigen are expected to be available four to six months after the company receives the H1N1 seed strain, subject to regulatory approval. The new vaccine will be tested in clinical trials.

In clinical studies using the H5N1 influenza strain, an adjuvanted formulation has been shown to stimulate a higher immune response while using a smaller amount of antigen as compared to a formulation without adjuvant. The adjuvant system therefore helps to increase the number of vaccine doses that can be produced.

GSK's H5N1 vaccine, which includes the AS03 adjuvant system, is currently approved in Europe and some Asian countries, GSK is working with US Food and Drug Administration (FDA) and other government authorities with regard to its adjuvant and A (H1N1) candidate vaccine development. Fifteen clinical trials are ongoing to generate additional data for the adjuvant system, including a trial programme for a seasonal influenza vaccine.

GSK continues to support governments and health authorities around the world with their response to the emergence of the new A (H1N1) influenza strain. The company is in ongoing discussions with several other countries regarding possible supply of its candidate A (H1N1) adjuvanted vaccine.

Adjuvants are compounds used to enhance a vaccine's ability to elicit a strong, durable, protective immune response making them more effective.