Evaluating the Infectivity, Safety and Immunogenicity of a Recombinant Live-Attenuated Respiratory Syncytial Virus Vaccine in RSV-Seronegative Infants 6 to 24 Months of Age

Human respiratory syncytial virus (RSV) is the most common viral cause of serious acute lower respiratory illness in infants and children under 5 years of age worldwide. This study evaluated 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 were 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 could be enrolled in the study between April 1 and October 14 (outside of RSV season) and remained on study until they completed the post-RSV season visit between April 1 and April 30 in the calendar year following enrollment. Participants' total study duration was between 6 to 10 months, depending on when they enrolled in the study. Participants attended several study visits throughout the study, which included blood collection, nasal washes, and/or physical examinations. Participants' parents or guardians were contacted by study staff at various times during the study to monitor participants' health.