GlaxoSmithKline said this morning that a vaccine that could help prevent an outbreak of the H5N1 'bird flu' virus had been approved by the European Commission.

The vaccine, Prepandrix, is the first which is meant to be used before an outbreak of the virus, which it is feared could kill large numbers of people.

GSK's profits from the vaccine will be determined by whether governments believe a 'flu pandemic is a real threat, more than 30 years after the last outbreak in Hong Kong.

Analysts believe that sales of the Prepandrix vaccine to governments, NGOs and companies, could reach as much as $1 billion (£511 million). Prepandrix sales are negotiated with goverments as long term contracts, which makes it difficult to determine how much GSK will make from the vaccine. Switzerland has ordered 8 million does to cover its entire population, while the US has ordered 27.5 million.

The H5N1 virus has killed 234 people since 2003, as well as thousands of birds, but has not yet mutated into a strain that can be easily passed from person to person, although GSK argues it is only a matter of time before a pandemic strikes.

Emmanuel Hanon, Head of Flu at GSK's vaccines business, said: "The chances are there will be another influenza pandemic soon. If you look at the twentieth century, a major outbreak happens every 30 to 40 years."

Humans with the disease are most often treated with Tamiflu, made by Roche. Sanofi Pasteur, the joint venture between Sanofi Aventis and Merck, has also produced a vaccine that targets one strand of H5N1.

GSK argues that their vaccine is the first to target several strains of the virus.

Prepandrix contains an adjuvant, an ingredient that allows a low level of the vaccine's active ingredient to be used in each shot. This makes it easier to manufacture large supplies of the vaccine quickly in the event of an outbreak.

GSK has developed a strategy to make the vaccine available to poorer countries.

Jean-Pierre Garnier, the outgoing chief executive of GSK, said: "We will sell our vaccine at a favourable price to countries that otherwise won't get access to it. Countries can apply for funding to various entities such as the Gates foundation or other governments."

GSK has also donated 50 million doses of the vaccine to the World Health Organisation.

The company has already sold 3.3 million doses to the UK government. Finland, Switzerland and the US have also ordered doses of the vaccine, and the company is currently in negotiations with several other countries about supplying them with Prepandrix.

The Royal College of General Practitioners has recommended that the Department of Health should vaccinate all patients in at-risk groups, such as poultry workers, healthcare workers and the elderly, with a pre-pandemic H5N1 vaccine to help protect against an influenza pandemic.

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