A former CDC vaccine expert says the government may have to ration available flu vaccine after British health officials abruptly pulled the license of a major supplier.

Dr. Walt Orenstein, now the associate director of the Emory Vaccine Center in Atlanta, notes that it is already October, which is vaccine season.

Orenstein says being forced to ration at this stage would complicate the entire flu vaccine program.

U.S. health officials warned of major flu shot shortages Tuesday after British authorities suspended the license of Chiron Corporation, which supplies half of the flu vaccine in the United States, for three months.

The suspension stems from problems at Chiron's vaccine manufacturing plant in Liverpool, England, which primarily supplies the American market.

The action means the company can't supply any flu vaccine during that time, and Chiron said it would provide no U.S. vaccine this year.

British officials didn't explain details for the license suspension.

Chiron officials said the British action came because of broad concerns about standards at the Liverpool factory, not just worries about the safety of already produced vaccine.