Respiratory syncytial virus: virology, diagnosis, and vaccination.

Attempts to develop a respiratory syncytial virus vaccine have revealed the antigenic heterogeneity of the virus and have highlighted the difficulties of inducing protective responses in very young infants. Of the two subgroups of the virus, A and B, that cocirculate, A appears to be the most aggressive in infants, but protection against both will be required. Although a degree of protection is transferred from mother to the infant via the placenta and by breast feeding, the mechanisms of protection remain ill-understood and early hopes of exploiting this phenomenon have not been realized. The immune response to the virus in the very young is depressed but disease severity is not demonstrably linked to failure to control virus replication. Rather, immune mechanisms contribute directly to the development of bronchiolitis. The involvement of the immune response in the pathologic process increases the hazards of vaccination. Research is currently focused on the definition of viral epitopes necessary to induce only a protective immune response and their incorporation into a suitable vaccine vector.