PHILADELPHIA--Production of the nation's supply of flu vaccine has been delayed up to two months and supplies will be short during the best time to protect patients, pharmaceutical firms and public health officials said yesterday.

The companies blame that on late notification from the federal Centers for Disease Control (CDC) on what type of vaccine would be needed this year. The CDC says the problem stems from the fact that some of the viruses causing this year's flu take unusually long to cultivate for vaccines.

The largest producer of the vaccines, Wyeth Laboratories Inc., of St. Davids in suburban Philadelphia, usually has shipped the bulk of its 9 million doses by September.

This year, Wyeth will be sending vaccine to physicians through early to mid November, said company spokesperson Audrey Ashby. Then it will take additional time to get people in for their shots.

October and November are considered the best times for immunization.

The highest risk group for the flu, and traditionally last on the list of those immunized, are older people living in close quarters in big-city nursing homes, said Paul StehrGreen, an immunologist with the CDC in Atlanta.

Immunized Last

They need their flu shots by middle to late November, he said. Doctors prefer to immunize them last because their systems do not hold on to the antibody as long as younger people's, he said.

"If they don't get it in time, there's a risk of an influenza epidemic" among older people, he said.

The drug makers said they were late in gearing up vaccine production because of late notification from the CDC on the strains that will need to be targeted this flu season. Also, some of the strains targeted by the CDC require a vaccine that takes longer to produce than usual.

"We didn't learn about the final strain until much later than normal," said Marshall Molloy, spokesperson for Morris Plains, N.J.-based ParkeDavis, another flu vaccine maker. He said the notification usually comes in February but didn't come until April this year.

The CDC was a month later than usual in identifying the three prevalent strains, according to Beth Waters, spokesperson for Connaught, a Swiftwater-based pharmaceutical firm.

Suzanne Gaventa, an epidemiologist with the CDC, denied the federal agency was late in notifying the drug companies. She said the strains to be targeted were identified in conjunction with the World Health Organization and published in the CDC's Morbidity and Mortality Weekly Report April 22. She said the decision is routinely made in March or April.