WASHINGTON (Reuters) - Half of those hospitalized with the new H1N1 virus are under 25, a clear illustration that the pandemic is affecting the young disproportionately, U.S. health officials said on Tuesday.

They said reports from 27 U.S. states show 53 percent of people sick enough to be hospitalized with H1N1 flu are under the age of 25, with only 7 percent of hospitalizations among people 65 and older.

“This is really, really different from what we see with seasonal flu,” the CDC’s Dr. Anne Schuchat told reporters. “With seasonal flu, about 60 percent of hospitalizations occur in people 65 and over.

She stressed the report was incomplete but said if anything, it was underestimating the extent of the pandemic.

And an analysis of 292 deaths from 28 states showed that younger people than usual are also dying, she said.

“Almost a quarter of deaths are occurring in young people under the age of 25. Specifically, 23.6 percent of the deaths are in that age group. About 65 percent of the deaths are in people 25 to 64 years of age,” Schuchat said.

Just 12 percent of deaths were among people over 65. In a normal year, 90 percent of those who die from flu are over 65.

With cooler weather, other viruses and infections are showing up, making the picture confusing.

Schuchat said influenza is being diagnosed in about 30 percent of all people showing up with “influenza-like illness,” symptoms that include cough, sore throat, fever and aches.

Almost all influenza is turning out to be H1N1 rather than seasonal influenza and Schuchat said the tests often miss cases of H1N1, so the percentage may be higher.

Ordinary colds, group A streptococcus, which causes “strep throat”, and other infections can cause similar symptoms.

The U.S. government is trying to vaccinate people against both seasonal influenza and H1N1 at the same time, making both vaccines available as manufacturers finish, bottle and get them approved batch by batch.

Five companies make both types for the U.S. market: Sanofi-Aventis SA, CSL Ltd, Novartis AG, GlaxoSmithKline and AstraZeneca unit MedImmune.

Schuchat said H1N1 vaccine was becoming available slowly.

“As of yesterday, 12.8 million doses were available for the states to order. More than half of that was available in the injectable form. So that’s helpful, with giving us a variety of formulations,” she said.

She said states had ordered 10.8 million doses so far.