Administration of a highly attenuated, live respiratory syncytial virus vaccine to adults and children.

A highly attenuated respiratory syncytial virus (RSV) experimental vaccine, RSV ts-2, was sequentially evaluated in adults, seropositive children, and finally, fully susceptible seronegative children. The vaccine was administered intranasally in doses ranging from 10(5.2) to 10(6.3) PFU/ml. In both adults and children, the vaccine proved to be poorly infectious. Although poor infectivity would not have been predicted from tissue culture studies of RSV ts-2 growth, the human experience closely parallels the experience in a series of animal models, including the chimpanzee. The poor infectivity of this RSV vaccine virus preparation suggests that the postulated defect in the RSV ts-2 fusion protein may be important in determining in vivo infectivity of RSV.