MedImmune Inc. said on Thursday that an easier-to-store version of its nasal spray flu vaccine FluMist met the main goal of a late-stage trial, which was to show that it worked as well in protecting against the flu.

FluMist, which was approved in 2003, has had disappointing sales, in part because it needs to be kept frozen. The new version, called CAIV-T, only needs to be kept refrigerated. The study is a key step in the company’s plan to file for regulatory approval for CAIV-T in healthy people ages 5 to 49.

MedImmune said the phase III study tested 980 people who received either CAIV-T or FluMist. Results showed equivalent antibody levels after vaccination.

FluMist’s sales have also been restricted because it is not approved for very young children or the elderly, the most important markets for the vaccine. The company is working on additional studies to assess CAIV-T in children 6 months to 5 years of age.