MedImmune, Inc. announced today that it has initiated a pivotal head-to-head Phase 3 clinical trial designed to compare its next-generation, refrigerator- stable intranasal influenza vaccine (CAIV-T: cold adapted intranasal influenza vaccine, trivalent) with the injectable flu shot (TIV: trivalent influenza vaccine).

The company also announced that it has completed enrollment in a bridging study designed to establish that CAIV-T, the refrigerator-stable form of its live, attenuated intranasal influenza technology, is equivalent to its currently marketed frozen formulation, FluMist (Influenza Virus Vaccine Live, Intranasal).

"With the advancement of these studies, we remain on course with our influenza vaccine development program," said Edward M. Connor, M.D., executive vice president of clinical development and chief medical officer at MedImmune, Inc. "These trials will provide pivotal data regarding the safety and relative efficacy of our intranasal vaccine compared to TIV, as well as data regarding the comparative safety and immune responses for the frozen and the refrigerator-stable formulations of FluMist. MedImmune remains hopeful that it will deliver an improved option for the prevention of influenza disease, particularly for children."

Phase 3 Head-to-Head Study

The Phase 3 head-to-head trial is a randomized, double-blind study that will compare the safety and relative efficacy of CAIV-T to TIV during the 2004/2005 influenza season. The study will be conducted at approximately 300 sites in the Northern Hemisphere. Approximately 7,000 children across 18 countries between the ages of 6 months through 59 months will be randomized one-to-one in this study to receive either CAIV-T or TIV. All participants will receive both an intranasal mist and an intramuscular injection to preserve the double-blind design of the study.

Bridging Study

MedImmune´s bridging study is a double-blind, randomized trial designed to establish the equivalent immunogenicity and safety of MedImmune´s two live, attenuated intranasal formulations (refrigerator-stable and frozen). The study is being conducted at 31 sites in the United States. In this study, 977 healthy participants between the ages of 5 and 49 years have been randomized one-to-one to receive either CAIV-T or FluMist. Participants 5 through 8 years of age will receive two doses of study vaccine, while those 9 through 49 years of age have received one dose of study vaccine.

Additional CAIV-T Studies

To date, the safety, tolerability and efficacy of CAIV-T has been studied in a number of trials involving populations between the ages of 6 weeks and 98 years, including healthy persons and persons at high-risk of complications due to influenza. Data from several of these trials showing that the vaccine was safe and effective in reducing the incidence of community acquired influenza in the populations studied were presented in October 2003 at the Fifth Annual Options for the Control of Influenza Conference. Further, data from two Phase 3 trials involving a total of 4,400 children with a history of respiratory illness or asthma were presented in May 2004 at the Pediatric Academic Societies?annual meeting, showing that CAIV-T provided superior protection with a similar safety profile to the injectable flu vaccine.

Post-Marketing and Additional Safety Studies with FluMist

To collect additional safety and efficacy on its currently marketed live, attenuated intranasal influenza vaccine, MedImmune is advancing a Phase 1 placebo-controlled trial in 20 immunocompromised children with cancer, as well as a Phase 1/2 trial comparing FluMist to TIV in 300 HIV-infected children. The HIV trial is being conducted in collaboration with the Pediatrics AIDS Clinical Trials Group (PACTG).

A number of post-marketing studies for FluMist are also underway, including: several trials in elementary schools in Washington, Texas, Maryland and Minnesota to determine the direct and indirect impact of FluMist immunization among school-aged children and their families; a Phase 4, open- label, single-arm trial to assess the shedding, immunogenicity and safety of FluMist in healthy individuals 5 to 49 years of age; a large safety surveillance trial that will enroll at least 60,000 individuals between 5 and 49 years of age over multiple influenza seasons at participating Kaiser Permanente centers in Northern California and Colorado; and a community-based, non-randomized, open-label trial to assess safety and herd immunity in approximately 5,000 healthy children between 5 and 17 years of age in Central Texas.

About Influenza

In a typical year, influenza is responsible for an average of 36,000 deaths (primarily in the elderly) and 200,000 hospitalizations in the United States. Children have the highest rates of influenza infection of any age group during the flu season and are important disseminators of the influenza virus into communities. According to the Centers for Disease Control and Prevention (CDC), 152 children younger than 18 years of age died in the United States from influenza and its complications during the 2003-2004 flu season. Seventy-one percent of these children had no high-risk medical conditions, as defined by the CDC. Influenza vaccination of all healthy children 6-23 months of age and their close contacts is now routinely recommended by the CDC´s Advisory Committee on Immunization Practices.

About FluMist

FluMist is the first live, attenuated influenza vaccine indicated for active immunization for the prevention of disease caused by influenza A and B viruses in healthy children and adolescents, 5 to 17 years of age, and healthy adults, 18 to 49 years of age.

There are risks associated with all vaccines, including FluMist. FluMist does not protect 100-percent of individuals vaccinated, or may not protect against viral strains not represented in the vaccine. FluMist is contraindicated in persons with hypersensitivity to any component of the vaccine, including eggs; in children and adolescents receiving aspirin therapy or aspirin-containing therapy; in individuals with a history of Guillain-Barre syndrome; and in individuals with known or suspected immune deficiency. The safety and efficacy of FluMist have not been established in pregnant women or for patients with chronic underlying medical conditions, including asthma or reactive airways disease; the vaccine should not be administered to these patients. See Prescribing Information for indications and usage, dosage and administration and safety information.

MedImmune´s Commitment to Innovation

FluMist represents the first new influenza vaccine introduced to the U.S. since 1945. It is also the first nasally administered vaccine for any disease approved by the U.S. Food and Drug Administration. Nearly $1 billion has been invested to date to bring to market the first new innovation in flu prevention in nearly 60 years. Twenty-one clinical trials involving more than 30,000 subjects have already been completed for FluMist. Twenty-one additional trials involving an additional 34,000 subjects have already been completed for the next-generation, refrigerator-stable formulation of FluMist, known as CAIV-T. MedImmune currently has an additional eight clinical trials involving more than 70,000 subjects underway for FluMist and CAIV-T.

About MedImmune, Inc.

MedImmune strives to provide better medicines to patients, new medical options for physicians, rewarding careers to employees, and increased value to shareholders. Dedicated to advancing science and medicine to help people live better lives, the company is focused on the areas of pediatric infectious diseases, cancer and inflammatory diseases. With approximately 1,900 employees worldwide, MedImmune is headquartered in Maryland. For more information, visit the company´s website at http://www.medimmune.com/.

This announcement may contain, in addition to historical information, certain forward-looking statements that involve risks and uncertainties. Such statements reflect management´s current views and are based on certain assumptions. Actual results could differ materially from those currently anticipated as a result of a number of factors, including risks and uncertainties discussed in MedImmune´s filings with the U.S. Securities and Exchange Commission. The company is developing several products for potential future marketing. There can be no assurance that such development efforts will succeed, that such products will receive required regulatory clearance or that, even if such regulatory clearance is received, such products will ultimately achieve commercial success.

MedImmune, Inc.

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