The Food and Drug Administration has ordered MedImmune Inc. to stop distributing a promotional flier for its nasal flu vaccine FluMist because, the agency said, it misled consumers by not disclosing the product's side effects and how it is used.

"By failing to include sufficient information on risks and adequate directions for use, you have encouraged the potentially unsafe use of FluMist," the FDA wrote in a letter issued June 21 and released on the agency's Web site yesterday.

Jamie P. Lacey, the spokeswoman for the Gaithersburg biotech firm, said the firm stopped distributing the fliers after receiving the letter last week. Asked whether some of the fliers were still in doctors' offices, Lacey said that the firm was working with the FDA "to correct the situation."

The flier was designed as a way of "helping physicians gauge how much influenza vaccine they would need for the upcoming flu season," Lacey said. It specifically asked patients whether they preferred a standard flu shot or FluMist.

But while the flier acknowledged that "there are risks associated with all vaccines, including FluMist," it did not identify specific risks cited in the product label, including that it shouldn't be used by people sensitive to eggs or by those with suspected immune deficiency or chronic underlying medical conditions.

The warning letter also chided MedImmune for not providing adequate directions for using FluMist. Asked why the information the FDA was seeking was not included in the flier, Lacey said: "We have a process in place that includes medical, legal, and regulatory review. Beyond that I don't have specifics."

FDA officials declined to elaborate on the letter. The agency typically issues one or two warning letters a month to drug companies for violating restrictions on marketing material.

The flier was the latest stumble in MedImmune's attempts to market the nasal vaccine. Last year, MedImmune chief executive David M. Mott described the FluMist launch to investors as a "debacle of the first order."

MedImmune spent $25 million on an ad campaign promoting the launch for the 2003-04 flu season. It made 4 million doses and priced them at more than double the cost of a flu shot. But the company sold fewer than 500,000 doses.

This past flu season, MedImmune planned to produce only 1 million to 2 million doses, and it cut the wholesale price from $46 to $23.50 a dose. But in October, Chiron Corp. announced that it could ship less than half of the U.S. flu shots needed because of manufacturing problems in England.

Federal health officials hustled to find more vaccine, and encouraged the use of FluMist, which is approved for healthy people ages 5 to 49. The company increased its production to 3 million doses but wound up selling about 2 million.

MedImmune officials have not said how much FluMist they will produce for the 2005-06 flu season.

MedImmune doesn't expect FluMist to contribute meaningfully to the company's bottom line until 2007, when the company hopes to launch a new version of the vaccine that is approved for children under age 5 and doesn't have to be frozen. The lack of such approvals has impeded FluMist's widespread adoption.

Earlier this month, the company announced that the new version works just as well when stored in a refrigerator as the old one does when it is frozen. The firm is awaiting results, expected later this year, on tests using the refrigerated version on children 6 months to 5 years old.

MedImmune stock closed yesterday at $27.18 a share, up 25 cents.

FluMist doses are packaged at MedImmune's Philadelphia plant. The Food and Drug Administration told the company to stop distributing a promotional flier.