A gene deletion that up-regulates viral gene expression yields an attenuated RSV vaccine with improved antibody responses in children.

Respiratory syncytial virus (RSV) is the leading viral cause of severe pediatric respiratory illness, and a safe and effective vaccine for use in infancy and early childhood is needed. We previously showed that deletion of the coding sequence for the viral M2-2 protein (ΔM2-2) down-regulated viral RNA replication and up-regulated gene transcription and antigen synthesis, raising the possibility of development of an attenuated vaccine with enhanced immunogenicity. RSV MEDI ΔM2-2 was therefore evaluated as a live intranasal vaccine in adults, RSV-seropositive children, and RSV-seronegative children.