McFarland EJ, Karron RA, Muresan P, et al. - For meeting the necessity of vaccine against the respiratory syncytial virus (RSV), Live RSV vaccine D46/NS2/N/ΔM2-2-HindIII, attenuated by deletion of the RSV RNA regulatory protein M2-2, was developed on the basis of previous candidate LID/ΔM2-2. However, it incorporates prominent differences vs MEDI/ΔM2-2 which was more restricted in replication in Phase 1. One intranasal dose [105 plaque forming units (PFU)] of D46/NS2/N/ΔM2-2-HindIII (n = 21) or placebo (n = 11) was administered to RSV-seronegative children ages 6-24 months. Then the children were monitored for vaccine shedding, reactogenicity, RSV-antibody responses and RSV-associated medically-attended acute respiratory illness (RSV-MAARI) and antibody responses during the following RSV season. Infection with vaccine was identified in all 21 vaccinees; of these, 20 (95%) shed vaccine. Findings here suggest excellent infectivity and immunogenicity of D46/NS2/N/ΔM2-2-HindIII, and further, it primed for anamnestic responses, encouraging further evaluation of this attenuation strategy.