RecruitingBiological interventionA Study of BLB-201 RSV Vaccine in Infants and ChildrenThis Phase 1/2a trial is a randomized, placebo-controlled trial to evaluate the safety, tolerability and immunogenicity of two ascending doses (10\^6 PFU and 10\^7 PFU) of intranasal BLB-201 (a recombinant parainfluenza virus type 5) administered in infants (8-24 months of age) and children (18-59 months of age) who may or may not have had prior respiratory syncytial virus (RSV) infection.