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 LID cp ΔM2-2, a recombinant live-attenuated RSV vaccine, in RSV-seronegative infants 6 to 24 months of age.~Participants were randomly assigned to receive a single dose of the RSV LID cp ΔM2-2 vaccine or placebo at study entry (Day 0).~Participants were 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 and 10 months, depending on when they enrolled in the study. Participants attended several study visits throughout the study, which may include 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.~The study was closed to accrual early after interim data were reviewed by a subset of protocol team members and it was concluded that this vaccine candidate will not meet the criteria listed in the protocol for a good vaccine candidate. This recommendation was shared with the (blinded) protocol chair and the Medical Officers, as well as the Data Safety and Monitoring Board (DSMB), who agreed with the unblinded protocol team members' assessment. The targeted sample size was 33 (22 in the vaccine arm and 11 in the placebo arm). Participants already on study at the time of the early closing decision remained on study and completed the follow-up per protocol.
The purpose of this study was to evaluate the safety, infectivity, and immunogenicity of a single intranasal dose of a recombinant live-attenuated respiratory syncytial virus (RSV) vaccine in RSV-seronegative infants 6 to 24 months of age.~This study was a companion study to CIR 312.