(AP) -- The swine flu pandemic is spurring makers of seasonal flu vaccines to ship them to the U.S. market well ahead of schedule, and supplies are tightening as distributors and others snap up vaccine vials.

The top U.S. supplier of , Sanofi Pasteur, stopped taking orders for 10-dose vials of Fluzone, which make up about 60 percent of its production, on June 19, spokesman Len Lavenda said Wednesday.

"Last year, we had them available through Thanksgiving," Lavenda told The Associated Press. "That's a huge difference."

Sanofi, Novartis AG and PLC all have begun shipments of seasonal flu vaccine earlier than usual, with Glaxo and Novartis both starting shipments Wednesday and Sanofi on July 27. Novartis said it was starting "weeks ahead of schedule;" Sanofi is about two weeks early, and Glaxo is a little ahead of its normal mid-August start.

The companies cite expectations of increased demand due to concerns about the global , plus the need to clear the deck for making . Also, doctors and clinics will face quite a challenge in trying to vaccinate patients first against seasonal flu and then give what is expected to be a series of two shots against swine flu.

Despite the early shipments and apparent heavy demand, there is no need for people who want a seasonal flu vaccine to panic, said Dr. Henry Bernstein, a member of the American Academy of Pediatrics' committee on .

"I think there's going to be a more than adequate supply to administer the vaccine to everyone that wants it," Bernstein said.

When swine flu, or novel H1N1 , first surfaced this spring, flu vaccine makers said they were worried about being able to make enough of two different vaccines, one against the new strain and one against the three strains of seasonal flu expected to circulate.

But the companies appear to have risen to the challenge - although Glaxo has had technical problems that will reduce its expected production from about 27.5 million to 20 million doses.

Sanofi Pasteur of Swiftwater, Pa., part of French drug giant Sanofi-Aventis SA, had a little luck this year: It just got a new manufacturing plant in Swiftwater, in the Pocono Mountains, approved in May. Instead of closing the older one for a planned renovation, it has been running both factories "24 hours a day, seven days a week," Lavenda said, noting the company has hired about 200 additional workers there and is looking for more for the two plants.

"One is making seasonal (vaccine) and the other is making H1N1" concentrate in bulk, he said.

Production of the H1N1 vaccine began back in June, after the Centers for Disease Control and Prevention supplied manufacturers with virus samples needed to begin growing the H1N1 virus in eggs. Once the federal government tells vaccine makers the exact dose to be in each shot, it can be packaged into vials or syringes and labeled for shipment, Lavenda said.

Sanofi Pasteur is producing about 50 million doses for the U.S. market, the same as last year.

Switzerland's started production earlier than usual this year, according to spokeswoman Beth Birke.

"We have accelerated our efforts tremendously," Birke said in an e-mail, increasing resources "to ensure seasonal supply and our ability to expeditiously switch over to H1N1."

The company plans to supply 30 million doses of its Fluvirin vaccine.

GlaxoSmithKline started shipping its Flulaval vaccine Wednesday and will soon start shipping another one called Fluarix. It had a lower-than-expected yield of one of the vaccine strains, and has had to tell customers it can't fill all their orders.

One is Henry Schein PLC, believed to be the largest supplier to doctors' offices. Schein now expects to get 9 million instead of 13 million doses, but Executive Vice President Steven Paladino said it may try to get more later in the season.

"We've seen very strong demand from our customer base," he said, citing awareness of .

MedImmune, an AstraZeneca PLC subsidiary that sells a nasal spray seasonal flu vaccine, started shipments on July 28, about normal for the company. It plans to distribute about 10 million doses.

The Food and Drug Administration said Wednesday it has cleared a total of 70 lots of flu vaccine, made by five different manufacturers, for distribution. Lots typically range from 500,000 to 600,000 doses each, meaning roughly 38.5 million doses already have been cleared. About 120 million doses are expected to be available this year.

Dr. Jonathan Temte, a family physician at the University of Wisconsin at Madison and a member of the federal Advisory Committee on Immunization Practices, said much of the flu vaccine supply is routinely ordered early in the year, but he thinks large HMOs, university clinics and drugstore chains have been making big orders to get patients in early.

Doctors, other providers and schools will have to work together and start seasonal flu vaccines in August or September, ahead of the usual schedule of October or November, to handle the logistical difficulties of two types of vaccines, Temte said.

"We don't know how to ratchet up the system" to do that, he said.

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