Companies starting work on H1N1 vaccine- CDC

* Clinical trials would start in coming months

* Vaccine would not be ready until October

By Julie Steenhuysen

CHICAGO, May 28 (Reuters) - Companies are starting preliminary work on a vaccine for the new H1N1 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.

Although new to humans, they said, the H1N1 strain appears to be behaving very much like a seasonal H1N1 flu in striking more children and young people.

So far, there have been 8,585 probable and confirmed U.S. cases of the the new H1N1 strain, commonly called swine flu, with 12 deaths and 507 hospitalizations, Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention said in a telephone briefing.

She said the CDC shipped virus samples for making vaccines to different manufacturers several days ago.

The strains were made using traditional vaccine methods, which involve live vaccines made in chicken eggs, and a new, proprietary reverse genetics method that allows companies to make non-live vaccines, avoiding working with potentially highly infectious pandemic strains.

AstraZeneca's (AZN.L) MedImmune unit owns the reverse genetics method, which it has licensed to a number of companies approved to sell flu shots in the United States including Sanofi-Aventis SA (SASY.PA), Novartis AG (NOVN.VX) and GlaxoSmithKline Plc (GSK.L).