RSV is the most common viral cause of serious acute lower respiratory illness (LRI) in infants and children under 5 years of age in the world. RSV illness can range from mild upper respiratory tract illness (URI) to severe LRI, including bronchiolitis and pneumonia. Severe RSV disease in infancy may also predispose children to develop reactive airway disease during childhood. The purpose of this study is to evaluate the safety and immunogenicity of an RSV vaccine (RSV LID ΔM2-2) in RSV-seronegative infants and children at least 6 months and through 24 months of age.~To determine study eligibility, the screening process will include a blood collection. At study entry, eligible participants will be randomly assigned to receive one dose of either the RSV vaccine or placebo, which will be delivered as nose drops. Participants will also undergo a review of medical history, clinical assessment, and a nasal wash. They will then receive their assigned vaccine and will remain under observation for monitoring for 30 minutes after receiving the vaccine. Additional study visits will occur at Days 3, 5, 7, 10, 12, 14, 17, 19, 21, 28, and 56. These visits will include clinical assessments and nasal washes; on Day 56, a blood collection will also occur. On days where no study visit is scheduled (through Day 27), participants' parents or guardians will report participants' temperatures and signs of illness to researchers by e-mail or phone.~In October following vaccination, participants may have a pre-RSV season blood collection visit. During RSV season, November through March following vaccination, researchers will contact participants' parents or guardians on a weekly basis for follow-up monitoring. During this time frame, participants seen by a medical provider for fever, respiratory illness, or otitis media will have a study visit, which will include a nasal wash and clinical assessment. In April following vaccination, participants will undergo a final blood collection.
Respiratory syncytial virus (RSV) is a common cause of illness in infants and children around the world. This study will evaluate the safety and immune response to an RSV vaccine in RSV-seronegative infants and children.~This study is a companion study to IMPAACT 2000.