A federal advisory panel voted to recommend limited Food and Drug Administration approval of MedImmune Inc.'s nasal-spray influenza vaccine yesterday, an important next step for the Gaithersburg company, which has staked its plans for growth on delivering the drug to pharmacy shelves.

MedImmune didn't get everything it wanted -- the advisory panel rejected its argument that FluMist is effective for anyone over 50 years old, and MedImmune withdrew its application for approval for use by those under 5. The panel said the drug, which contains a live flu virus, should be marketed only to healthy people ages 5 to 49, which excludes the important markets of the youngest and oldest populations, which are most vulnerable to flu.

MedImmune acquired FluMist when it bought California biotechnology firm Aviron in January for $1.5 billion. At the time skittish investors were wondering where the firm would find its next moneymaker. The company's infant respiratory drug, Synagis, earned it $516 million in 2001, accounting for 83 percent of its sales.

"We are breathing rarefied air as one of the few companies that has followed an initial product success with a second product," said David M. Mott, MedImmune's chief executive.

FluMist now heads to the FDA, which typically endorses advisory-panel findings. Because the panel wasn't entirely supportive of the product, questions remain about whether the public will abandon the old standby, the flu shot. MedImmune hopes to have the vaccine approved in time for the 2003-2004 flu season.

"FluMist has the potential to replace the traditional flu shot," said Dennis Harp, a biotechnology analyst at Deutsche Bank Securities Inc., which estimates MedImmune will sell $125 million worth of the product next year. "The shot will not go away completely, but for the larger, healthy population, FluMist might become the preferred vaccine."

Trading in MedImmune shares was halted on the Nasdaq Stock Market yesterday in anticipation of the panel's meeting. Shares fell $1.65, or 6.2 percent, to $24.99 on Monday.

FluMist, which is being co-developed with Wyeth, may be a pain-free alternative to an annual flu shot, but it's likely to have a higher price tag. Industry analysts believe FluMist will cost at least $25 a dose, rather than the $5 to $10 usually charged for shots.

The 18-member advisory committee said that although they found the drug safe, there was insufficient data to measure its effectiveness in patients older than 50. It recommended MedImmune collect more data on that age group.

Even those who voted to approve FluMist for older patients, such as Walter L. Fagget, director of the D.C. Department of Health, called the company's data for the 50-to-64-year-old age group "barely adequate." Barbara Loe Fisher, president of the National Vaccine Information Center, voted against approval for all ages. The information, she said, "suggests that an unknown number of individuals across all age groups will not be able to handle this vaccine well."

In all, 20,228 patients have received doses of FluMist in human tests. The most common side effects were runny nose and nasal congestion, company officials said. In addition, doctors cannot rule out the possibility that FluMist could accidentally infect high-risk individuals once it's ingested.

In a study of 1,600 healthy children ages 15 months to 6 years, where patients received the vaccine or a placebo, FluMist proved 93 percent effective in preventing the flu, the company reported. For most patients, the recommended dose is expected to be a single squirt in each nostril, once a season.

The same FDA advisory panel declined to support FluMist two years ago when Aviron failed to debunk a possible link between FluMist and pneumonia. MedImmune purchased Aviron with its eyes on easy FDA approval for FluMist, said Jill Kiersky, a biotechnology analyst at Morningstar Inc. But MedImmune's application moved slowly through the regulatory process, and the company missed a projected product launch in 2002.