Evaluating the Infectivity, Safety, and Immunogenicity of a Single Dose of a Recombinant Live-Attenuated Respiratory Syncytial Virus Vaccine (D46/NS2/N/ΔM2-2-HindIII) 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 (LRI) in infants and children under 5 years of age worldwide. This study evaluated the safety, infectivity, and immunogenicity of a single dose of RSV D46/NS2/N/ΔM2-2-HindIII, a recombinant live-attenuated RSV vaccine, in RSV-seronegative infants and children 6 to 24 months of age. Participants were randomly assigned to receive a single dose of the D46/NS2/N/ΔM2-2-HindIII vaccine or placebo (administered as nose drops) at study entry (Day 0). Participants could be enrolled in the study outside of RSV season (between April 1 and October 14 for most sites or-for sites with local RSV seasons that start earlier-as specified on a site-by-site basis in the Manual Of Procedures). All participants 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 and 13 months, depending on when they enrolled in the study. Participants attended several study visits throughout the study, which included physical examinations, blood collection, and nasal washes. Participants' parents or guardians were contacted by study staff at various times during the study to monitor participants' health.