The nasal spray version of the H1N1 vaccine will be available in the U.S. sooner than planned, said Rear Admiral Dr. Anne Schuchat. (John Bazemore/Associated Press)

The U.S. will start administering the first doses of a nasal spray version of the swine flu vaccine early next week, health officials say.

The FluMist nasal spray is approved for people aged two to 49 who do not have asthma, said Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention.

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

The first 600,000 doses of the nasal spray will be shared by 21 states and four large cities by Tuesday. Smaller shipments will be delivered later in the week. The amount of vaccine that is available and who receives it will change weekly, Schuchat said.

"We're moving this out as quickly as we can," said Oregon's public health director, Dr. Mel Kohn, who hopes shipments arrive in time to begin some vaccinations on Monday. "This doesn't do any good sitting in a warehouse."

H1N1 cases in U.S. 'striking'

The plan is for larger batches of shots and spray to start shipping in the second week of October, when states will be able to start offering the vaccine to groups at high risk from the H1N1 strain — pregnant women, children and young adults, people with conditions like asthma and diabetes, and caregivers of infants.

State health departments submit orders for the H1N1 vaccine to the federal government, which has bought the U.S. supply. It's up to states to decide where to give the shots, such as at doctors' offices, hospitals, pharmacies and public clinics.

Meanwhile, the H1N1 virus is already causing cases across the United States.

"What we are seeing is quite striking," Schuchat said.

In contrast, Health Minister Leona Aglukkaq said Wednesday that levels of H1N1 in Canada remain low to moderate, with a small number of hospitalizations from flu that are expected at this time of year.

The strain is not deadlier than seasonal flu but is causing more severe disease among younger people.

The CDC will track the shipments to ensure that the people at highest risk are vaccinated.

Canada expects to start administering GlaxoSmithKline's H1N1 vaccine in early to mid-November. Provinces and territories have different plans for giving out seasonal and H1N1 shots.

On Thursday, Ontario Health Minister David Caplan urged the federal government to speed up licensing of the H1N1 vaccine as the U.S. has done.

Australia started administering the vaccine this week.

With files from The Associated Press