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. The purpose of this study is to evaluate the safety, infectivity, and immunogenicity of a single dose of a recombinant live-attenuated RSV vaccine, RSV LID ΔM2-2 1030s, in RSV-seronegative infants 6 to 24 months of age.~Participants will be randomly assigned to receive a single dose of the RSV LID ΔM2-2 1030s vaccine or placebo (administered as nose drops) at study entry (Day 0).~Participants will be enrolled in the study between April 1 and October 31, outside of the 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. Total study duration is between 6 to 13 months, depending on when participants enroll in the study. Participants will attend several study visits throughout the study, and the visits may include blood collection, nasal washes, and physical examinations. 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 6 to 24 months of age.~This study is a companion study to IMPAACT 2011.