Ten months after filing for approval of its second-generation FluMist influenza vaccine, MedImmune Inc. received a complete response letter from the FDA requesting more information on data already submitted.

The Gaithersburg, Md.-based company plans to respond to the agency within two to four weeks, meaning the new formulation - called CAIV-T (cold adapted influenza vaccine, trivalent) - could still be available for use in next year's influenza season.

"The questions are somewhat technical in nature," said Jamie Lacey, MedImmune's director of public relations, adding that the 2007-2008 season "remains our targeted and our anticipated launch time frame."

MedImmune did not give specifics on what the FDA is requesting, but investors did not seem worried. The company's stock (NASDAQ:MEDI) closed Tuesday at $25.86, down 8 cents.

The company filed the supplemental biologics license application for CAIV-T in September. If approved, the product could redeem FluMist, the first-generation intranasal vaccine that has proved to be disappointing at best. MedImmune posted FluMist sales of just $21 million in 2005, significantly below the $1 billion potential projected by MedImmune when it acquired the product through its $1.5 billion purchase of Mountain View, Calif.-based Aviron Inc. in 2002. Even analysts, at the time, considered FluMist to be a multi-$100 million product at peak.

A major advantage of CAIV-T - other than its intranasal delivery - is that, unlike FluMist, it does not need to be stored frozen, offering an easier administration.

"We believe that the refrigerator-stable formulation will be more convenient," Lacey told BioWorld Today. "And then in our trial comparing CAIV-T to the flu shot, the data suggest that it is a better vaccine, and so we believe that all of those things together will prepare us to provide an important option to the marketplace."

MedImmune has given no sales guidance for the product.

In Phase III trials, CAIV-T has demonstrated that it's 55 percent more effective than the flu shot in reducing influenza illness. It is not yet known whether it's more effective than the first-generation FluMist product.

"The intent of this submission is to show that they're immunogenically equivalent," Lacey said. The sBLA "has more to do with how it's stored than the vaccine itself."

The filing under review by the FDA aims to gain approval of CAIV-T in preventing influenza in healthy individuals ages 5 to 49 years.

But MedImmune also plans to position the product as a vaccine that can be used in children younger than 5, something it never did for FluMist. The company intends to file a separate sBLA to the FDA within a few weeks, including data from a Phase III study of about 8,500 children between 6 months and 59 months of age. The hope is to launch the second-generation product with the expanded indication at the same time.

Earlier this month, MedImmune received FDA approval of an sBLA to use reverse genetics technology to construct new vaccine strains to produce seasonal influenza vaccines, such as CAIV-T. Use of reverse genetics, the company said, enhances the safety, specificity, reliability and efficiency with which new vaccine strains can be produced. It enables researchers to avoid working directly with infectious, circulating pandemic strains.

MedImmune owns and exclusively licenses key patent estates covering the use of reverse genetics technology in human influenza vaccines.

In June, the National Institutes of Health began enrolling subjects in a Phase I trial of an intranasal H5N1 influenza vaccine candidate based on MedImmune's live, attenuated vaccine technology, which also used reverse genetics technology. Researchers are hopeful that the technology will prove to be as effective in potential pandemic A strains as it is in seasonal matched and mismatched A strains of influenza.