* Clinical trials would start in coming months
* Vaccine would not be ready until October
* US could authorize adjuvant, CDC official says (Adds second official on use of adjuvant)
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).
Schuchat said in coming weeks companies will start making "candidate lots" of vaccine which will be used for clinical trials. "Those will happen over the summer months," she said.
Clinical trials will need to answer a number of questions, Schuchat said, including whether one or two injections will be needed, whether vaccinating different age groups yields different results and whether an immune system booster called an adjuvant would be needed to get a good response.
Michael Shaw, associate director of the CDC's Laboratory Science Influenza Division, told Reuters on the sidelines of a conference on swine flu in New York that a vaccine could be "stretched" by using an adjuvant, allowing more doses to be made.
"There are a couple of adjuvants that are being looked at now. There's nothing that's been approved for use in the United States, but there are several that could possibly get emergency use authorization if it appeared it was called for," he said.
WAITING FOR STUDIES
She said companies are also developing bulk ingredients needed to make vaccine doses should the CDC decide a vaccine is needed.
"The actual making of those doses needs to wait for the clinical studies to be finished," she said.
She said the decision on whether to produce large quantities of a vaccine would be made later in the Northern Hemisphere summer or early autumn.
The CDC and World Health Organization will be taking their cues from the way this flu behaves in the Southern Hemisphere, where flu season is just starting.
"Most of the people that are getting sick continue to be in that 5-to-24-year age group. That's 62 percent of all the cases that we're counting," Schuchat told the briefing.
She said it is still "relatively rare" for people over 55 to be infected, with only about 1 percent of probable cases in that age range.
While there is no question the flu strain is new, Schuchat said in some respects it is behaving a bit like the seasonal H1N1 flu strain that circulates every year.
"Seasonal H1N1 often causes more disease in younger people," she said.
She also gave details of how to tell who is at most risk of becoming severely ill with any respiratory disease, so they know when to seek immediate medical help.
Children who look blue or cannot be awakened should be taken to a doctor, she said. "Being so irritable that the child doesn't want to be held. Flu-like symptoms improve, but then return later with a fever and a worse cough," she said.
For adults, severe vomiting is a danger sign, as is sudden dizziness and chest pressure. (Additional reporting by Claudia Parsons in New York, Editing by Mohammad Zargham)