GlaxoSmithKline, a London-based firm, has finally won U.S. approval to sell its vaccine to fight H1N1 influenza, which is also known as swine flu. A unadjuvanted H1N1 vaccine, which is currently scarce, has been allowed to ship next month in relatively larger amounts to the United States next month.

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

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

Glaxo is one of the world's largest manufacturers of flu vaccines, along with Sanofi-Aventis SA (SASY.PA) and Novartis AG (NOVN.VX). Other manufacturers of swine flu vaccines have long received approvals for the sales; Glaxo was left out as it is challenging to make a vaccine without an adjuvant and U.S. officials have decided not to use adjuvants in their immunization program.

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