U.S. health officials said on Thursday more than 6 million doses of H1N1 swine flu vaccine will be available the first week of October, twice as many as they expected only a week ago.

But even as officials ramp up vaccine production, they say most Americans tend not to bother getting vaccinated -- especially the children and young adults most at risk of being infected by the newH1N1 virus.

We really need to get the message out, U.S. Health and Human Services Secretary Kathleen Sebelius told reporters.

Taking the risk and getting sick is probably not a wise roll of the dice, she said. People can die, and the people who are going to be ill and die are much more likely to be children and young adults.

The U.S. government expects to have 6 million to 7 million doses of vaccine available the first week of October, up from an estimate of 3.4 million doses last week. Most of the early doses will be MedImmune's nose spray.

Another 40 million doses should be available in mid-October with production continuing at a rate of 10 million to 20 million doses per week to a total of more than 250 million by year end.

The United States has ordered vaccine from five companies -- MedImmune, a unit of AstraZeneca, Sanofi-Aventis, Australia's CSL, GlaxoSmithKline and Novartis.

Meanwhile, hopes dimmed for the world vaccine supply on Thursday. The World Health Organization reduced its estimate of vaccine production capacity from 5 billion doses a year to 3 billion, enough for only half the planet.

HEALTH RISK

The U.S. Centers for Disease Control and Prevention has designated certain people to be vaccinated first. They include school-aged children, pregnant women and people with underlying conditions such as heart disease, asthma or diabetes.

At least 46 U.S. children under 18 have died from H1N1 swine fluinfection since April, when the disease was first detected in the United States. Usually, between April and October, no U.S. children die from influenza.

H1N1 became a pandemic in June and has infected millions of people in the United States, the CDC's Dr. Anne Schuchat said.

Sebelius said public reluctance to accept vaccination could itself pose a health risk.

She said that typically, fewer than 25 percent of children and pregnant women get vaccinated against seasonal flu, which kills about 250,000 to 500,000 people a year worldwide.

Vaccination rates are also below 30 percent for young adults and around 40 percent for healthcare workers.

An American Red Cross survey released last month showed that only 11 percent of Americans were very worried about the new swine flu while another 29 percent were somewhat worried. The rest -- 60 percent -- said they were not worried.

Swine flu is already widespread in 21 U.S. states. But the virus so far is proving to be milder than expected, with a death rate similar to that of seasonal flu.

Sebelius sought to emphasize the dangersswine flu poses for vulnerable groups by warning that many of the 36,000 deaths that occur in the United States during mild flu seasons could be children this time around.

We are not making this up. This is serious, she said. Parents need to understand.

So far, about 15 percent of children hospitalized for swine flu have required intensive care, Schuchat said.

Tests show the swine flu vaccine closely matches the H1N1 virus, which suggests it will protect people well. Children also respond to the vaccine just as they do the seasonal flu, meaning those over 10 need one shot while children 9 and under need two.

Australia Medicine