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 infectivity, safety, and immunogenicity of two recombinant live-attenuated RSV vaccines: RSV ΔNS2/Δ1313/I1314L and RSV 276. The vaccines were delivered as nose drops to RSV-seronegative infants 6 to 24 months of age.~Participants were randomly assigned to receive a single dose of the RSV ΔNS2/Δ1313/I1314L vaccine, the RSV 276 vaccine, or placebo at study entry (Day 0).~Participants could be enrolled in the study outside of RSV season, i.e., 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. 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, nasal washes, and/or nasal adsorption (nasosorption) specimen collection. Participants' parents or guardians were contacted by study staff at various times during the study to monitor participants' health.
The purpose of this study was to evaluate the infectivity, safety, and immunogenicity of the recombinant live-attenuated respiratory syncytial virus (RSV) vaccines RSV ΔNS2/Δ1313/I1314L or RSV 276 when delivered as nose drops to RSV-seronegative infants 6 to 24 months of age.~This study was a companion study to Center for Immunization Research (CIR) 321.