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CHICAGO, June 25 (Reuters) - French drug maker Sanofi-Aventis <SASY.PA> has begun large-scale production of a vaccine for the H1N1 swine flu at its facilities in the United States and France, the company said on Thursday.

Production of the vaccine for the new flu virus, which has caused a global pandemic, will use conventional egg-based vaccine technology, the company said in a statement. The statement did not specify how many doses of the swine flu vaccine the company is making.

Sanofi, which makes vaccines through its Sanofi-Pasteur unit, said dosage requirements for the vaccine will be based on clinical trials expected to take place during the summer in the northern hemisphere.

The announcement came as the company addressed a meeting of the Advisory Committee on Immunization Practices, which advises the U.S. Centers for Disease Control and Prevention.

Sanofi, which has said it makes 40 percent of the world's supply of flu vaccine, said it is continuing to make seasonal influenza vaccine for the 2009/2010 northern hemisphere flu season, as recommended by the U.N. World Health Organization.

Production of seasonal flu vaccine for both northern and southern hemispheres is still a priority, the company said.

Seasonal influenza causes an estimated 250,000 to 500,000 deaths per year worldwide.

Sanofi has said that at full capacity, its two Pennsylvania factories can make 150 million doses of seasonal influenza vaccine a year. Its French plant can make 120 million doses per year, according to Sanofi.

Governments have pledged billions of dollars for a vaccine to combat swine flu. The United States has set aside $1 billion. The Netherlands ordered 34 million doses and Australia has ordered 10 million doses as the World Health Organization declared a pandemic.

Other companies that make flu vaccine include Novartis AG <NOVN.VX>, Baxter International Inc <BAX.N>, GlaxoSmithKline <GSK.L> and Solvay <SOLB.BR>.

(Reporting by Julie Steenhuysen, Editing by Will Dunham)

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