Human respiratory syncytial virus (RSV) is the most common viral cause of serious acute lower respiratory illness (LRI) in infants and children under 5 years of age worldwide. This study will evaluate the safety, infectivity, and immunogenicity of a single dose of RSV LID cp ΔM2-2, a recombinant live-attenuated RSV vaccine, in RSV-seronegative infants and children 6 to 24 months of age.~Participants will be randomly assigned to receive a single dose of the RSV LID cp ΔM2-2 vaccine or placebo at study entry (Day 0).~Participants will be enrolled in the study between April 1 and October 31 (outside of RSV season) and will remain on study until they complete the post-RSV season visit between April 1 and April 30 in the calendar year following enrollment. Participants' total study duration will be between 6 and 13 months, depending on when they enroll in the study. Participants will be evaluated in study visits that may include physical examinations, blood collection, and nasal washes. Additionally, participants' parents or guardians will be contacted by study staff at various times during the study to monitor participants' health.
The purpose of this study is to evaluate the safety, infectivity, and immunogenicity of a single dose of a recombinant live-attenuated respiratory syncytial virus (RSV) vaccine in RSV-seronegative infants and children 6 to 24 months of age.~This study is a companion study to IMPAACT 2012.