MedImmune Inc. received long-awaited news late Tuesday afternoon as the FDA approved FluMist, a nasally delivered product that has ridden a rocky road throughout the regulatory review process.

The agency signed off on the first live influenza virus vaccine approved in the U.S. to prevent illness from A and B strains of the flu in healthy children and adolescents between the ages of 5 and 17, as well as in adults from 18 to 49. The FDA stipulated that children between 5 and 8 should receive two doses at least six weeks apart in their first year on the drug, while individuals from 9 to 49 should receive a single dose of the spray, which is delivered into each nostril.

Gaithersburg, Md.-based MedImmune said FluMist would be available beginning late this summer and early fall, in time for this year's flu season. The company is banking on its nasal delivery as an attractive alternative to the more traditional flu shot. The FDA added that its availability could free up supply of the injected, killed virus vaccine for those most at risk - infants and the elderly.

"We're very excited that the product has been approved and that we have an opportunity to bring it to the marketplace," MedImmune President and Chief Operating Officer Melvin Booth told BioWorld Today. "We're really pleased that there really is a light at the end of the tunnel."

The product, which contains three strains of live, attenuated, cold-adapted, temperature-sensitive influenza virus - two Type A (H1N1 and H3N2) and one Type B - will be marketed through an ongoing global collaboration agreement between MedImmune's wholly owned subsidiary, MedImmune Vaccines Inc., and Wyeth Pharmaceuticals.

"FluMist really offers a new way to assist in the prevention of influenza in healthy children and adults," Booth said. "There are approximately 160 million healthy children and adults between the ages of 5 and 49 in the U.S."

MedImmune Vaccines will manufacture between 4 million and 6 million units of FluMist this year, with capacity planned to eventually expand to between 18 million and 20 million, Booth said.

Marketing plans include education of physicians, pharmacists and other health care workers, as well as patients, and broad direct and indirect advertising efforts. Its agreement with Madison, N.J.-based Wyeth predates its involvement with the drug. MedImmune acquired FluMist as part of its $1.5 billion merger with Aviron Inc. a year and a half ago. At the time, analysts pointed to MedImmune's desire to acquire the drug in time for the coming year's flu season. (See BioWorld Today, Dec. 4, 2001.)

But the timing didn't quite work out as planned.

Problems related to the approval process first surfaced after Mountain View, Calif.-based Aviron submitted its biologics license application in October 2000, as questions eventually arose during subsequent panel presentations. One voted 13-2 in favor of the drug's efficacy in 18- to 64-year-olds, though it was split (8-7 against) in 1- to 17-year-olds. But a lack of safety data proved a more significant problem, as the panel voted 9-5 that safety data were insufficient in 1- to 64-year-olds. (See BioWorld Today, July 30, 2001.)

MedImmune then dealt with two subsequent complete response letters from the FDA - the company submitted answers in August 2001 and July 2002. And early this year, the FDA handed down another complete response letter seeking clarification and additional information relating to previously submitted data. But MedImmune stressed that the five-question letter did not request additional trials - a factor the company viewed as a good sign. (See BioWorld Today, Jan. 31, 2002.)

Just a month earlier, MedImmune had received favorable feedback from the FDA's Vaccines and Related Biological Products Advisory Committee, which voted positively on questions of FluMist's safety and efficacy in people between 5 and 49. A majority of the 18-person panel also gave its safety a thumbs-up in the 50- to 64-year-old population, but only four agreed that it was efficacious in that group. (See BioWorld Today, Dec. 18, 2002.)

But clinical data have borne out FluMist's efficacy in the approved age groups. A study of 60 people between 18 and 41 showed that FluMist protected adults 85 percent of the time in those intentionally exposed to wild-type virus. Data from a two-year, 544-patient pediatric field trial found its efficacy in preventing flu was 87 percent among healthy children between 5 and 7 (p< 0.05).

MedImmune's future plans for the drug include expanding its label into broader age groups. Booth said the company initially would focus on 50- to 64-year-olds, with studies spanning two flu seasons in the works.

"We will put the plan together and get concurrence from the FDA, and that will probably take a couple of seasons to do," he explained. "We'll also focus on those under 5, which will probably take an additional season."

The news was released after the market closed Tuesday. MedImmune's shares (NASDAQ:MEDI) dropped $1.02 Tuesday to close at $38.71.