CHICAGO (AP) -- Baxter International Inc., based in Deerfield, Ill., is working on a new flu vaccine that could be grown without the eggs. It hopes to have it on the market in Europe next year and in the United States perhaps by 2007, assuming approval from the Food and Drug Administration.

More than 80 million Americans got a flu shot this year, and tens of millions of chickens surrendered their eggs to make that possible.

The flu vaccine is made by growing flu virus inside a chicken egg, a technology that's been around for decades.

Baxter says the advantages of its so-called "vero cell" flu vaccine would include the company not having to buy millions of eggs, fewer problems with egg allergies that prevent a small portion of people from being able to receive a flu shot, and preventing the likelihood, however small, of transmitting diseases from chickens to people through a flu vaccine.

But Aventis Pasteur, the vaccines business of Aventis and the world's largest producer of the current flu vaccine, says egg-based technology has worked well for years and there's no reason to change. The company has looked into the very same vero cell technology Baxter is researching and hasn't found a way to make it cost effective.

Baxter, which doesn't currently sell a flu vaccine, says it will grow the flu virus inside huge fermenters. A single tank, the company says, can produce as much flu virus as one million eggs, without the hassle.

"It's certainly a wonderful opportunity for us," said Kim Bush, president of Baxter's vaccines business, a part of the company's BioSciences division. "We're ramping up production capability."

Influenza causes approximately 36,000 deaths and 114,000 hospitalizations each year, according to the Centers for Disease Control and Prevention. More than 90 percent of deaths occur among people age 65 and older.

Baxter anticipates being able to make 10 million to 15 million doses in 2005, and 40 million to 50 million doses by 2007. The product is a $200 million to $400 million opportunity for the $8.5 billion company, Baxter says.

For the last 30 to 40 years, flu virus has been grown in chicken eggs. When a fertilized egg is eight to nine days old, it's injected by needle with a tiny bit of flu virus, which then grows in the egg and is harvested one or two days later. A single egg is needed to make one dose of vaccine containing a multitude of flu viruses, and major flu vaccine makers like Aventis Pasteur and Chiron Corp. need tens of millions of eggs every year.

About 4 percent of the population is allergic to eggs, according to Baxter, and many of these people can't get a flu shot.

However, allergist Lee Sonin, who practices in the Chicago suburbs, said his office sometimes gives the flu vaccine even to patients who are allergic to eggs because the danger to them from the flu virus is even greater than the danger from the vaccine.

Baxter also notes that the current vaccine has a long production cycle. Every year, the World Health Organization has to decide which three flu strains the vaccine should protect against, and because of the long production cycle, must make its decision around August.

But if Baxter's vero cell flu vaccine becomes a popular alternative, the company says, its shorter production cycle could mean more flexibility for the WHO when it decides which strains to target.

Baxter's product is also free of animal proteins. That means there's little chance of any kind of disease getting spread by the vaccine from animals to humans.

Another advantage, Baxter says, is a more reliable supply of vaccine. Sometimes, chicken disease outbreaks can kill huge numbers of animals, hurting egg production.

Aventis says chicken diseases aren't a major problem.

Chiron, the second-largest flu vaccine company, is also working on a cell culture vaccine. It expects to enter Phase III trials in Europe next year.

The company says current technology imposes limits on output.

"You have to order your eggs many months in advance, and your yield is limited by the volume of eggs you've ordered," said John Gallagher, a spokesman for Chiron.

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