Although regular flu vaccine does not protect against bird flu, some people mistakenly believe that it does. Rising fears over a global pandemic could be partly responsible for a surge in demand for flu shots.

The company had to call off 3,300 to 3,600 clinics, about 10% of the total planned for the year. "We couldn't find enough [vaccine] to continue to support those events," Wright said.

Maxim, which vaccinates about 2 million people a year, has asked its corporate clients to delay workplace clinics by three to four weeks in hopes that more vaccine is available later in the season.

Chiron Production Delayed

Vaccine maker Chiron, whose license was suspended last year because of contamination at its factory, has been cleared to produce vaccine but says production has been delayed. It can't say how much vaccine it can make this year, but it will be less than the 18 million originally projected. Chiron has shipped at least 5 million doses.

Other makers are on track, says Lola Russell, a spokeswoman for the Centers for Disease Control and Prevention. She said Sanofi Pasteur has delivered 51 million doses and expects to ship a total of 62 million; Glaxo-SmithKline shipped 7.5 million; and MedImmune, which makes the nasal spray vaccine, has sent out 1 million doses with 2 million more to come.

Stories About Avian Flu

In October, the CDC advised flu shots only for people at high risk of flu complications, mainly the very young, the elderly and the ill. But after Oct. 24, when clinics were opened to all comers, Wright said, demand "actually went up another 30%. There was a lot of pent-up energy ready to go, all the people in the non-high-risk categories."

Kaiser Permanente Colorado also has experienced a jump in demand; it has distributed 100,000 of its supply of 150,000 doses in just two weeks, said Eric France, chief of preventive medicine. "I think some of that [demand] comes from news stories about avian flu," he said.

Flu Season Peaks Around January

Avian flu is a strain spreading among birds in Asia and Eastern Europe that experts fear could mutate and cause a human flu pandemic. Regular flu vaccine does not protect against the avian strain.

But infectious-disease specialist Mary Young of Georgetown University Hospital in Washington, DC, says at least some patients might believe the annual flu shot prevents avian flu. "This year, because of all the talk about avian influenza, people seem more eager to get flu vaccine. I'm not sure if there's confusion about the two, or if they just understand the seriousness of influenza."

The CDC says flu season peaks around January, so there's time to get a flu shot, even in December. CDC director Julie Gerberding is expected to give an update Thursday on vaccine demand and shortages, Russell says.