Prevention of infections with respiratory syncytial virus: the hopes and hurdles ahead.

Control of infections due to respiratory syncytial virus (RSV) by immunization poses special problems. First, the peak period of serious illness due to RSV is during the first few months of life, and thus a vaccine would have to be administered during the neonatal period. Second, we understand little of the pathogenesis of and immunity to RSV disease in newborns, and an immune reaction may even play a role in the development of the lower respiratory tract disease seen in infancy. Third, immunity to RSV is imperfect even after naturally acquired, severe infection of the lower respiratory tract. Therefore, it is difficult to envision a vaccine that is safe in the infant and that will engender more complete immunity than the disease itself. However, if the goals are limited to protection of certain high-risk groups or to protection of infants during the first year of life only, immunization might be both feasible and effective in reducing the morbidity and mortality associated with this ubiquitous virus.