A new strain of flu virus called “A California” will be added to the mix used in the U.S. vaccine for next season, which is already causing anxiety after a shortage in the current season.

Food and Drug Administration advisers on flu vaccines agreed on Wednesday that the U.S. vaccine should include the California strain to replace the Fujian strain, which produced a surprisingly early and strong flu season in 2003-2004 but which has not made a large number of people ill this season.

The new California strain is in a family of H3N2 viruses and is already infecting people around the globe, said Dr. Nancy Cox, an influenza expert at the U.S. Centers for Disease Control and Prevention.

“H3N2 viruses always cause us a lot of headaches,” Cox told the meeting. “They are responsible for more severe influenza seasons, generally speaking, including higher numbers of hospitalizations and deaths.”

The two other strains will remain unchanged from last year - “A New Caledonia” and “B Shanghai.”

The usually quiet process of choosing the cocktail for next season’s flu vaccine has come under fresh scrutiny with this season’s vaccine shortage, caused by contamination problems at Chiron Corp.‘s flu-vaccine plant in Britain, as well as the unusually early previous flu season.

Flu seasons usually start in September-October in the Northern Hemisphere and end in February-April. The current season is off to a late start and hasn’t yet peaked.

Adding to the anxiety is the avian flu epidemic among birds in several Asian countries, especially Thailand and Vietnam. Flu experts are racing to test a vaccine against the H5N1 strain of bird flu, which is usually lethal when it infects people.

Dr. Pamela McInnes of the National Institute of Allergy and Infectious Diseases said the agency had filed for FDA permission to begin testing two bird-flu vaccines in people, one made by Chiron and another by Sanofi Aventis.

Although the bird flu has mutated since it first appeared in 1997, she said the companies designed their vaccines to match the currently circulating avian flu virus, which has infected 55 people and killed 42 of them.

THREAT OF SHORTAGE

The threat of another U.S. vaccine shortage still looms, the experts said.

Chiron is still working to clear up the troubles at its vaccine plant that led to contamination and it is not clear it can finish in time to start making next season’s vaccine.

A spokesman for Sanofi Aventis said his company could make no more than 50 million or 60 million doses of vaccine for next year. If more sources of vaccine are not found, that will mean another year of rationing.

The CDC defended its vaccine strategy, which urged people over 65 to get shots first, along with babies, the chronically ill and other groups.

A report this week in the Archives of Internal Medicine that suggested elderly people - the main target of flu-vaccination campaigns - are not really protected by flu vaccines.

The CDC and the National Foundation for Infectious Diseases said the report was misinterpreted and actually highlighted a need for more elderly people to be vaccinated.