RSV is the most common viral cause of serious acute lower respiratory illness (LRI) in infants and children under 5 years of age around the world. RSV illness can range from mild upper respiratory tract illness (URI) to severe LRI, including bronchiolitis and pneumonia. The purpose of this study is to evaluate the safety and immunogenicity of a single dose of a RSV vaccine in healthy children. Study researchers will first evaluate the vaccine in healthy RSV-seropositive children, then evaluate the vaccine in healthy RSV-seronegative infants and children, followed by younger infants not screened for RSV serostatus.~This study will first enroll healthy RSV-seropositive children ages 12 to 59 months (Group 1). At study entry, participants will undergo a medical history review, physical examination, blood collection, and a nasal wash procedure. Participants will be randomly assigned to receive either the RSV vaccine or placebo vaccine, administered as nose drops. Subjects will be actively monitored for 28 days following administration of vaccine or placebo; monitoring will include medical history reviews, clinical assessments, and at some visits, nasal washes. On the days where no study visit is scheduled, study researchers will contact participants' parents or guardians for medical follow-up.~Study researchers will evaluate the study data of participants in Group 1 before enrolling participants in Group 2, and study data from Group 2 will be reviewed before enrolling participants in Group 3. Finally, study data from Group 3 will be reviewed before enrolling participants in Group 4. Participants in Groups 2 and 3 will include healthy RSV-seronegative infants and children ages 6 to 24 months. Participants in Group 4 will include healthy infants, ages 4 to 6 months, who have not been screened for RSV serostatus.~Participants in Groups 2, 3, and 4 will be randomly assigned to receive either the RSV vaccine or placebo vaccine, administered as nose drops. Subjects will be actively monitored for 56 days following administration of vaccine or placebo; monitoring will include medical history reviews, clinical assessments, and at some visits, nasal washes. On the days where no study visit is scheduled, study researchers will contact participants' parents or guardians for medical follow-up. At a study visit on Day 56, participants will undergo a medical history review, blood collection, and a nasal wash procedure.~For participants in Groups 2, 3, and 4, from November through March following each participant's vaccination visit, parents or guardians will monitor participants for RSV-associated illnesses and report these on a weekly basis via telephone calls to study researchers. Participants may have additional study visits that may include blood collection and/or nasal wash procedures during this follow-up period. Participants in Groups 3 and 4 will have the option to take part in additional monitoring for a second RSV season.
Human respiratory syncytial virus (RSV) is a common cause of respiratory illness in infants and children around the world. This study will evaluate the safety and immune response to a RSV vaccine in three groups of participants: healthy children who have already had an RSV infection (RSV seropositive), healthy infants and children who have not already had an RSV infection (RSV seronegative), and healthy younger infants who have not been screened for prior RSV infection.