Live subgroup B respiratory syncytial virus vaccines that are attenuated, genetically stable, and immunogenic in rodents and nonhuman primates.

Optimal immunization of neonates against disease caused by respiratory syncytial virus (RSV) probably will require multiple doses of a vaccine containing viruses of both subgroups A and B. Live subgroup B RSV mutants were generated containing multiple attenuating mutations, ts (temperature-sensitive) and non-ts (host range), that were introduced by prolonged passage in cell culture or by chemical mutagenesis. The cold-passaged (cp)-52 mutant was restricted in replication compared to wild type virus in rodents and nonhuman primates. In addition, the attenuation phenotype of cp-52 was stable after prolonged replication in immunosuppressed rodents. One or two ts mutations were then introduced into the cp-52 mutant to generate additional candidate vaccine strains that were more attenuated in vivo than the cp-52 parental virus. Tests in humans are being done to determine if one or more of the RSV B-1 mutants exhibit a satisfactory balance between attenuation and immunogenicity.