The US Food and Drug Administration (FDA) has approved GlaxoSmithKline's (GSK) first adjuvanted vaccine for the prevention of H5N1 influenza, also known as avian or bird flu.

The pandemic Influenza A (H5N1) Virus Monovalent Vaccine, Adjuvanted (also referred to as Q-Pan H5N1 influenza vaccine) is intended for use in people aged 18 years and older who are at increased risk of exposure to the H5N1 influenza virus.

The FDA has purchased the vaccine from GSK's subsidiary ID Biomedical Corporation (IDBE) of Quebec City, Canada, for inclusion within the National Stockpile for distribution by public health officials if needed.

The vaccine is composed of monovalent, inactivated, split A/H5N1 influenza virus antigen and GSK's AS03 adjuvant.

GSK vice president of Vaccines Development Bruce Innis said H5N1-related illness has thus far been rare, but life-threatening when it has occurred.

"GSK scientists approached this clinical development project driven by the recognition that the resulting vaccine might be needed in the future to help protect millions of Americans against pandemic flu illness," Innis said.

The FDA said that most avian influenza A viruses do not infect people but some viruses, such as H5N1, have caused serious illness and death in people outside of the US, mostly among people who have been in close contact with infected and ill poultry.

The vaccine is not for commercial use, rather it will be kept in the US national stockpile for distribution by public health officials if needed.

FDA also noted that the H5N1 component and the AS03 adjuvant component are supplied in two separate vials, which must be combined prior to use.

The vaccine, which will be given to patients through intramuscular injection in two doses, 21 days apart, has also been authorised in Europe and Canada under the brand names, Pumarix and Arepanrix H5N1, respectively.