GlaxoSmithKline PLC said Monday that it has received permission from European medical regulators to market a human bird flu vaccine it has already sold to several governments to stockpile in preparation for a pandemic.

The ruling from the European Medicines Agency makes Prepandrix, which targets the H5N1 virus, the first vaccine to receive a license for pre-pandemic use in all 27-member European Union states.

Glaxo, which has already spent some $2 billion developing the vaccine, has orders from Switzerland and the United States for the vaccine based on the bird flu virus from Vietnam.

Switzerland has ordered 8 million doses — enough to cover the country's entire population. The U.S. Department of Health and Human Services has ordered 27.5 million doses.

Emmanuel Hanon, vice president of the Influenza Vaccine Franchise at Glaxo, said that Finland and several other European countries, who did not wish to be named, had also placed orders.

"This vaccine marks a significant step in the world's ability to cope with an influenza pandemic," said Glaxo Chief Executive Officer Jean-Pierre Garnier.

However, Glaxo is just one of several pharmaceutical companies, including Novartis SA and Sanofi Aventis, developing vaccines against H5N1 bird flu.

Experts believe H5N1, which has killed at least 241 people worldwide, is the most likely candidate to mutate into a pandemic virus.

Since late 2003, the virus has been circulating in Asia, Europe and Africa, and several distinct H5N1 strains have arisen.

Glaxo has said that its vaccine works against these other versions of the virus as well, announcing study results last year showing that that it even reacts against the Indonesian type of H5N1, a genetically different virus.

If a vaccine protects against different H5N1 strains, people could theoretically be pre-vaccinated before getting a booster shot with a new formulation containing the pandemic strain once the global outbreak strikes.

But if it is another flu subtype that causes the next pandemic, like H7 or H9, which have also caused human bird flu cases, vaccines created using the H5N1 strain will likely be useless.

Hanon said that the license from the EMEA equated to formal validation of the quality and efficiency of the vaccine.

"Having the license, I believe, is going to make a big difference," he said. "What we don't know is when the pandemic will come, but we do know that it will come."

Glaxo has agreed to donate 50 million doses of the vaccine to the World Health Organization in an attempt to create a pandemic vaccine stockpile for poor countries. The vaccines will be delivered over a three-year period and should provide enough doses for 25 million people as each person needs two shots per person.

Hanon said that full production capacity would be determined after an outbreak.