NEW YORK - GlaxoSmithKline Plc has won U.S. marketing approval to sell an unadjuvanted H1N1 swine vaccine, allowing it to ship relatively modest amounts of scarce vaccine to the United States next month.

The British company said on Tuesday the Food and Drug Administration had approved a modified version of its FluLaval seasonal flu vaccine containing the new H1N1 strain.

The green light clears the way for it to fill a order for 7.6 million doses from the U.S. government.

Glaxo is one of the world's largest manufacturers of flu vaccines, along with Sanofi-Aventis SA and Novartis AG .

But it is not a big source of swine flu vaccine for the United States, since its main H1N1 vaccine Pandemrix contains an adjuvant, or additive, and is not being used here.

The company's chief executive, Andrew Witty, told reporters last month that it would be only a "bit-part player in the U.S. flu scenario."

The 7.6 million doses of Glaxo's unadjuvanted vaccine, which is being manufactured in Canada, is just a small fraction of the 250 million doses ordered by the U.S. government.

Glaxo said it expected to start shipping its vaccine in December and complete deliveries by the end of the year.

Worldwide, Glaxo has taken orders for more than 440 million doses of its adjuvanted Pandemrix H1N1 vacccine.