MELBOURNE, May 29 (Reuters) - The United States has placed an order for $180 million worth of H1N1 flu vaccine from Australian pharmaceutical company CSL Ltd <CSL.AX>, CSL said on Friday, as the number of U.S. deaths from the virus reached 12.

CSL expects its H1N1 vaccine to be ready within a few months, with the company planning to start clinical trials to make sure the vaccine is safe and effective for human use.

Companies are starting preliminary work on a vaccine for the flu and should begin clinical trials in the coming months, but the new vaccine would not be ready for widespread use until October, U.S. health officials said on Thursday. See [ID:nN28367585].

Australia ordered 10 million doses of the CSL vaccine on Thursday as the number of confirmed H1N1 cases in Australia topped 100.

CSL's U.S. subsidiary CSL Biotherapies Inc. signed a contract with the U.S. Department of Health and Human Services to provide Novel A (H1N1) influenza vaccine antigen in bulk form, CSL said in a statement.

The new vaccine will be tested in clinical trials funded by HHS.

CSL shares last traded at A$29.03. (Reporting by Miranda Maxwell)

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