MedImmune, Inc. (Nasdaq: MEDI) today announced positive results from a large prospective trial conducted for prevention of respiratory syncytial virus (RSV). The trial compared motavizumab, the investigational monoclonal antibody (MAb) also known as Numax(R), with Synagis(R) (palivizumab), the standard of care for preventing RSV hospitalization in high-risk infants. In the Phase 3 study involving 6,635 pre-term infants at high risk for RSV, with a primary endpoint of non- inferiority, motavizumab demonstrated overall 26-percent fewer RSV hospitalizations compared with Synagis (p "I am very pleased with the study results for motavizumab," said Xavier Carbonell, M.D., Ph.D., lead study author, chairman of neonatology, Barcelona Hospital Clinic, and vice president, Spanish Neonatal Society. "As a practicing neonatologist, I look forward to the potential to use this next- generation antibody to help reduce RSV-related hospitalizations and LRIs in the outpatient setting."

Data from this trial demonstrate that both study drugs were well tolerated. The incidence and severity of adverse events (AEs) were comparable for both treatment groups and were consistent with prior experience with Synagis. There were comparable rates of related AEs and drug discontinuations between treatment groups [related AEs: motavizumab (N=298, 9.0 percent) vs. Synagis (N=258, 7.8 percent) p=not significant (NS); discontinuations: motavizumab (N=13, 0.4 percent) vs. Synagis (N=10, 0.3 percent) p=NS]. AEs related to skin hypersensitivity reactions resulted in discontinuation of dosing in motavizumab-treated patients at low frequency (N=9, 0.3 percent). In Synagis-treated patients, there were no AEs consistent with skin hypersensitivity reactions that resulted in dosing discontinuation. The overall mortality rates were not statistically different between the two groups (N=8, 0.2 percent motavizumab and N=4, 0.1 percent Synagis); no death was considered to be related to the study drugs and there were no RSV-related deaths. Immunogenicity in the motavizumab arm was less than 1 percent and comparable to the historical Synagis rate.

The trial was a randomized, double-blind study involving 6,635 high-risk infants at 347 centers in 24 countries through three RSV seasons. Study participants comprised premature infants born at 35 weeks gestational age or less who were six months of age or younger at randomization, as well as children with CLD related to prematurity requiring medical management within the six months prior to study entry, who were 24 months of age or less at randomization.

About RSV

Each year, an estimated 125,000 infants in the U.S. are hospitalized with severe RSV infections, the leading cause of lower respiratory tract infections in infants in the United States. RSV is the most common respiratory infection in infancy or childhood. Approximately one-half of all infants are infected with RSV during the first year of life, and nearly all children have been infected at least once by the time they reach their second birthday. Children born prematurely as well as those with CLD or congenital heart disease (CHD) are at highest risk for severe disease and hospitalization due to RSV. The virus may also cause severe illness in other high-risk groups such as the elderly, those with underlying respiratory or cardiac disease, and those with compromised immune systems (e.g., bone marrow transplant patients).

About Motavizumab

Motavizumab is an investigational humanized MAb being evaluated for its potential to prevent serious lower respiratory tract disease caused by RSV in pediatric patients at high risk of RSV disease. Phase 1 and Phase 2 study data have been reported showing that motavizumab appears to have a similar safety and pharmacokinetic profile to Synagis in infants. Additionally, in early phase studies children treated with motavizumab had reduced RSV replication in the upper respiratory tract.

About Synagis

Synagis is the only MAb approved by the U.S. Food and Drug Administration (FDA) to help prevent an infectious disease. Since its licensure in 1998, Synagis has been administered to more than 1,000,000 infants in the U.S. and has become the standard of care for infants at high risk for RSV. Synagis is indicated for the prevention of serious lower respiratory tract disease caused by RSV in pediatric patients at high risk of RSV disease, which is prominent in the Northern Hemisphere during the winter months. Synagis is a humanized MAb given by an intramuscular injection once a month during the RSV season. Synagis was approved in 1998 by the FDA; in 1999, by the European Medicines Evaluation Agency; and in 2002, by the Japanese Ministry of Health, Labor and Welfare. In 2003, the FDA expanded the U.S. label for Synagis for use in young children with hemodynamically significant CHD at risk of RSV disease. To date, Synagis has been approved in 62 countries, including the United States. Synagis is indicated for the prevention of serious lower respiratory tract disease caused by respiratory syncytial virus (RSV) in pediatric patients at high risk of RSV disease and is administered by intramuscular injection. Safety and efficacy were established in infants with bronchopulmonary dysplasia (BPD), infants with a history of premature birth (less than or equal to 35 weeks gestation age), and children with hemodynamically significant CHD. Synagis has been used in more than one million children in the U.S. since its introduction in 1998. The first dose of Synagis should be administered prior to commencement of the RSV season. Patients, including those who develop an RSV infection, should continue to receive monthly doses throughout the season.

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