Parenteral administration of live respiratory syncytial virus vaccine: results of a field trial.

A live respiratory syncytial virus (RSV) vaccine administered parenterally was evaluated for efficacy in a double-blind, placebo-controlled field trial in 510 children six to 47 months of age. Among the 233 recipients of live RSV vaccine, 68 of 98 initially seronegative children (as determined by enzyme-linked immunosorbent assay) developed antibody to RSV; 25 of the 30 initially seronegative children who did not develop antibody were less than 12 months old, which suggested that very low levels of maternal antibody (undetectable by enzyme-linked immunosorbent assay) inhibited replication of the vaccine virus. The children were monitored for the occurrence of naturally acquired RSV infection in two RSV epidemics, and there was no difference in the frequency of upper or lower respiratory tract disease caused by RSV between the live RSV vaccine recipients who developed vaccine-induced antibody and the placebo vaccine recipients. Thus, this live RSV vaccine administered parenterally was not efficacious.