The purpose of this study is to evaluate the infectivity, safety, and immunogenicity of the recombinant live-attenuated respiratory syncytial virus (RSV) vaccines RSV ΔNS2/Δ1313/I1314L or RSV 276 or placebo when delivered as nose drops to RSV-seronegative infants 6 to 24 months of age.
This study is a companion study to CIR 321.