U.S. health officials said Monday they are worried that an abundance of unused flu vaccine this year may lead to millions of doses being thrown out, discouraging manufacturers from making as much in the future.

They are urging Americans to get flu shots even after Thanksgiving — a time when public demand customarily drops off, even though the flu season typically doesn't peak until February.

"We are concerned that we're going to have more doses of flu (vaccine) than we might use," said Dr. Julie Gerberding, director of the Centers for Disease Control and Prevention.

More than 110 million doses — a record amount — are being made for the 2006-07 flu season. The previous record was 95 million in 2002-03. That year 12 million doses went unused and one manufacturer quit making shots.

CDC officials said they want to prevent a repeat of that experience and are promoting Nov. 27-Dec. 3 as "National Influenza Vaccination Week."

Between 5 percent and 20 percent of the U.S. population gets the flu each year, according to the American Medical Association. The illness leads to about 36,000 deaths and 200,000 hospitalizations each year, according to federal officials.

Flu shots are made by private companies, and both sides of the supply and demand equation for flu vaccine are complicated. CDC officials have tried to increase demand through public health campaigns and by expanding flu shot recommendations to include health care workers, pregnant women and children ages 6 months to 5 years.

Today, the CDC's flu shot recommendations cover 218 million of the nation's 300 million people, although only a fraction are expected to get them. The expanded recommendations helped lead to this year's record production.

However, even as federal officials urge almost everyone to get vaccinated, many people are unable to find a shot because of chronic distribution problems.

About 77 million doses were distributed by Nov. 3, but not every doctor or clinic got what they ordered. There are scattered shortages throughout the country. The Alabama Department of Public Health, for example, has received less than half its order for adults, and only about 30 percent of its order for children.

"We're having a problem," said Dr. Donald Williamson, Alabama's state health officer.

Meanwhile, an advocacy organization of parents with autistic children sounded a warning about thimerosal, a mercury-based preservative in most flu shots.

The group — PutChildrenFirst.org — held a teleconference with reporters Monday. They said few Americans understand that most flu shots contain thimerosal, which they contend contributes to autism and other disorders of emotional and intellectual development in children.

There is not good evidence proving such a cause-effect relationship, Gerberding said. The life-saving benefits of the vaccine far outweigh the risk alleged by PutChildrenFirst.org and similar groups, she added.

Thimerosal was phased out of other childhood vaccinations in 2003. But flu vaccine sold in multidose vials still contains the preservative.

About 9 million of this year's vaccine doses are thimerosal-free, a CDC spokesman said. Those doses — which are targeted for young children — are made by only one manufacturer, Sanofi Pasteur.

"Our organization is urging people not to get flu shots that contain thimerosal. And in this year's flu shot supply, 90 percent do contain thimerosal," said J.B. Handley, co-founder of PutChildrenFirst.org.

CDC officials said more thimerosal-free doses are not provided because demand for it has never met the supply. "It has never sold out," said Dr. Jeanne Santoli, deputy director of the CDC's immunization services division.

This is the first year of a California law that bans thimerosal from vaccines given to pregnant women and children younger than 3. But citing a shortage of thimerosal-free doses, the California Department of Health and Human Services this month suspended enforcement for six weeks, until distribution problems can be resolved.