Examining mortality statistics provides some perspective on the burden of RSV infection in children in developing countries, especially those under age 5. The causes of childhood mortality often change as a country develops. Initially, diarrheal diseases may be the leading cause of death. General development and the implementation of oral rehydration programs may reduce the impact of these diseases and increase the proportion of deaths due to respiratory infections. With further development, mortality from acute respiratory infections also begins to decline. The reasons for these shifts are complex, in part because of the effects of malnutrition and other risk factors.
Even with complete mortality statistics it is difficult to establish the role of RSV, because numerous other pathogens also cause respiratory infections in children. Parainfluenza viruses and adenoviruses produce similar symptoms. In addition, bacterial superinfections may occur and can contribute to mortality.
The disease burden estimates for RSV are shown in Table D-12.1 and are described in Appendix B. It should be emphasized that these are uncertain estimates because of the lack of data on RSV in developing countries. The association between acute lower respiratory tract illness from respiratory syncytial virus infection and the development of chronic obstructive pulmonary disease remains speculative (Glezen, 1984). No attempt has been made to estimate possible chronic morbidity associated with RSV infection.
Infants would be the principal target population for an RSV vaccine, because the most severe disease caused by the virus occurs early in the first year of life. This population could be reached through the World Health Organization Expanded Program on Immunization (WHO-EPI).
Other possible target populations include the elderly (Garvie and Gray, 1980) and older children with chronic cardiopulmonary disease (e.g., congenital heart disease, bronchopulmonary dysplasia, and asthma). RSV could be severe or fatal for children in this latter group at any age (MacDonald et al., 1982). Delivery of vaccine to pregnant or soon-to-be pregnant women may offer an alternative approach to immunizing young infants, if the latter proves not to be practicable.
A vaccine conferring temporary immunity might be acceptable for the major target population because the period of highest vulnerability is so brief (the first year of life).