UPDATE 1-Sanofi starts swine flu shot trial, files with FDA

* Sanofi U.S. clinical trials started Aug. 6

* Supplemental vaccine application filed with FDA

(Adds details, background)

LONDON, Aug 7 (Reuters) - Sanofi-Aventis SASY.PA, the world leader in flu immunisation, said on Friday it started human testing of its H1N1 swine flu vaccine on Aug. 6 and filed a supplemental licence application with U.S. regulators.

The French drugmaker's vaccine unit Sanofi Pasteur had told Reuters on Tuesday tests would begin "in days". Several other manufacturers have also started clinical trials recently, including Swiss-based Novartis NOVN.VX and Australia's CSL CSL.AX.

Sales of vaccines to contain the current swine flu pandemic are expected to provide a windfall for the global drugs industry, leading to billions of dollars in additional revenues in late 2009 and early 2010, according to industry analysts.

The World Health Organisation said on Thursday that the first vaccines to combat H1N1 flu should be approved and ready for use in some countries from next month.

Sanofi said its supplemental U.S. application requested the Food and Drug Administration to evaluate an influenza A(H1N1) 2009 strain change, which is expected to fast-track the approval process.

The company’s U.S. clinical trials will involve 2,000 subjects, who will be give both an ordinary version of the new vaccine and one including an additive designed to boost the immune system.

Reporting by Ben Hirschler; editing by John Stonestreet