RSV, a member of the Paramyxoviridae family of viruses, is a major cause of acute upper and lower respiratory tract infections in infants, young children, and adults. The virus is typically spread via respiratory secretions through close contact with contaminated surfaces and objects. The peak incidence of infections occurs in the winter months, usually coinciding with the influenza epidemic. Datamonitor estimates that annually, approximately 18 million people are infected with RSV in the seven major markets, including over 9 million children under the age of four, 5.5 million elderly, and 3 million adults with underlying disease. About 928,000 of these individuals become hospitalized due to their RSV infection. Further, an estimated 2.3 million children aged 0-59 months present with a RSV infection in the U.S. each year, of which approximately 91,000 are hospitalized. RSV infections are responsible for approximately 40 to 50% of hospitalizations for pediatric bronchiolitis and 25% of hospitalizations for pediatric pneumonia.
Only two drugs are currently available to either prevent or treat RSV infections. Antibody-based Synagis® (palivizumab) is approved to prevent, not treat, RSV infections in premature infants, and use is limited due to its cost. Ribavirin is used to treat serious RSV infections in infants with severe bronchiolitis and in immune-compromised patients. However, its use is also limited due to highly variable efficacy and toxicity risks. For instance, current American Academy of Pediatrics guidelines for the treatment of bronchiolitis in children do not recommend the routine use ribavirin due to lack of clinical evidence supporting its use. We believe there remains a significant unmet need for safe and effective RSV antiviral treatments in all RSV populations.