Most of the people who have died from the new pandemic H1N1 flu had underlying conditions such as asthma, but 45 percent seemed healthy, according to the largest study yet of U.S. cases.

Children with sickle cell and other blood diseases have a special risk from the swine flu, just as they do from seasonal influenza, Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention said on Tuesday.

She said injectable versions of the flu vaccine - suitable for babies, people with asthma and people 50 and older - will be available this week.

Schuchat said the CDC collected detailed data on 1,400 adults and 500 children hospitalized with swine flu in 10 states. The findings confirm that most serious cases and deaths have been in people under the age of 65.

“The vast majority of hospitalizations and deaths are occurring in younger people,” Schuchat told reporters in a telephone briefing. Five more children have died, bringing the H1N1 death toll among children in the United States to 81.

She said 55 percent of the adults had a condition known to worsen flu of all kinds. “In adults, the most common underlying conditions were asthma and chronic lung disease, chronic heart disease and immunosuppression,” Schuchat said.

Six percent were pregnant. Pregnant women have suppressed immune systems so their bodies do not reject the baby, and may also have pressure on the lungs from the fetus.

“And in children, the most common underlying conditions were asthma and chronic lung disease, neurological or neuromuscular diseases, and sickle cell or other blood disorders.”

Schuchat said 5.8 percent of hospitalized children had a blood disease related to red blood cells, such as sickle cell disease.

The CDC had not mentioned sickle cell disease before as a special risk, but such children had been highlighted in influenza guidelines as being at special risk and needing to be vaccinated every year.

9.8 MILLION DOSES

Schuchat said the vaccination program was continuing slowly. The CDC has opted to start immunizing people as soon as vaccine becomes available, which means supply has been spotty.

“As of yesterday, 9.8 million doses of the H1N1 vaccine were available to be ordered,” Schuchat said. States have ordered 5.8 million of these doses to go to providers.

“I’m happy to say that about half of the vaccine that’s available for order is now the injectable form,” she said.

So far the vaccine available for swine flu has been only AstraZeneca unit MedImmune’s nasal spray vaccine, which is only approved for people aged 2 to 49 without asthma or other lung conditions. States have been giving it to healthcare workers or older children.

Schuchat agreed that some places had experienced trouble getting either H1N1 or seasonal influenza vaccine quickly.

“It does take time to process the orders, to package them for the right amounts that are heading out towards the many sites we’ll be delivering vaccine, and this is going to be ongoing over the next days and weeks,” she said.

Vaccine would be more widely available at the end of October, Schuchat said.

She said there was no rush for people to be vaccinated against seasonal influenza.

“Right now we’re seeing the H1N1 strains. We aren’t seeing much at all of the seasonal strains. And we think there’s time to be vaccinated against the seasonal flu. Even if more vaccine isn’t available until November or December, we think it will be just fine to be vaccinated then,” she said.

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By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters)