In a recent study, 80 percent of the participants who were given the antigen developed a high immune response, according to the London-based company.

More Work to Protect Against Variants

"These excellent clinical trial results represent a significant breakthrough in the development of our pandemic flu vaccine," said JP Garnier, GlaxoSmithKline's chief executive officer. "This is the first time such a low dose of H5N1 antigen has been able to stimulate this level of strong immune response."

"There is still a lot more work to be done with this program, but this validation of our approach provides us with the confidence to continue developing the vaccine, including assessment of its ability to offer cross-protection to variants of the H5N1 strain. All being well, we expect to make regulatory filings for the vaccine in the coming months," he added.

Glaxo forecast that it could produce hundreds of millions of doses by 2007 and is waiting for approval by regulatory agencies before going forward.

When it becomes generally available, the vaccine will probably cost about as much as a conventional flu shot. The company reportedly is in talks with the Bill & Melinda Gates Foundation and the Global Fund to Fight Aids, TB and Malaria concerning financing arrangements for poverty-stricken countries.

Earnings Disappointment

The company also released its financial results on Wednesday, which failed to meet analyst expectations.

Garnier raised Glaxo's full-year earnings target from 10 percent to 12 percent, shy of the 15 percent target the market had been anticipating. The company's shares slipped on the news.

David Stout, the company's chief operating officer, commented that Glaxo has a history of giving conservative guidance, "which we have always exceeded or matched. We don't like to disappoint -- and I think a 20 percent upgrade to 12 percent is pretty good."