The very first doses of swine flu vaccine will start arriving in states and cities that ordered it on Tuesday, and might be sprayed up the first patients' noses by the end of the week, U.S. health officials said on Thursday.

Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention said the first U.S. H1N1 vaccine to be delivered will be 600,000 doses of a nasal spray made by MedImmune, a division of AstraZeneca.

This is a bit earlier than we were planning to get started, Schuchat said in a telephone briefing.

She said 25 states, counties or cities which had placed the first orders for H1N1 vaccine on Wednesday, would receive it on Tuesday and decide how to distribute it.

The nasal spray is only approved for people aged 2 to 49 who do not have asthma, but Schuchat said plenty of people could benefit from it anyway. The CDC is ordering flu vaccine from five makers and expects to get between 6 million and 7 million doses to its central U.S. distributor next week.

She said H1N1 pandemic flu was now widespread across the United States. What we are seeing is quite striking, she said.

While H1N1 is not any deadlier than seasonal flu, it is causing more severe disease among younger people than seasonal flu usually does, and could infect more people in the space of a few months.

PREGNANT WOMEN

Schuchat said 100 pregnant women had been hospitalized in intensive care with the virus and 28 had died. Pregnant women are at special risk from all forms of influenza.

As vaccine becomes available in appropriate formulations, we hope that pregnant women and their caregivers will take advantage of it, she said.

Immunization is considered to be the best method of preventing infection.

But once someone has the flu, the main treatment is the antiviral drug Tamiflu or oseltamivir, made by Roche AG under license from Gilead Sciences Inc.

She said the CDC had ordered 300,000 courses of liquid Tamiflu for children.

Some pharmacies had said they would start compounding liquid formulations for children because of reports of shortages of the pediatric formulation. Schuchat said even though the drug was past its stamped expiry date, the U.S. Food and Drug Administration had approved use of Tamiflu past this date.

So far each state that needs their proportion of that supply will receive this Tamiflu over the next week, Schuchat said.

People who have severe illness, who are hospitalized or have other warning signs can greatly benefit from antiviral medication, Schuchat added.

The CDC says most people will recover from H1N1 with no treatment but people who have trouble breathing, children who have trouble being awakened or who turn gray or blue, should all get immediate help.

The Trust for America's Health predicted on Thursday that 15 U.S. states cold run out of hospital beds if H1N1 infects just 35 percent of the population in coming weeks.

Pennsylvania Medicine