periodic epidemics of dengue fever. Tourists and military personnel visiting dengue endemic areas would also probably receive the vaccine, but their numbers are small compared to the major populations at risk.

Of the estimated 1.5 billion people living in areas endemic for dengue fever and areas that have recently had epidemics, about 38 percent, or 570 million, are under the age of 15 and would require vaccination in the initial years. Assuming a crude birth rate of 32 per 1,000 population, 48 million infants would need vaccination in all subsequent years.

There appears to be no insurmountable problem associated with incorporating dengue vaccine into the World Health Organization Expanded Program on Immunization (WHO-EPI) in appropriate areas.

Some cases of DHF occur in children under 1 year of age, most often between 6 and 12 months. For calculations it is assumed, though it is not yet certain, that it will be possible to vaccinate successfully children 6 months of age or younger.

The major risk of disease occurs after infancy even in endemic areas. Hence, in DHF/DSS endemic areas, 100 percent of the disease burden could be prevented by a vaccine that was 100 percent effective and that could be successfully administered to the entire target population at an early age. Herd immunity has not been studied in dengue infections, but it is possible that the disease burden could be eliminated even if vaccine coverage were not complete.

Disease-induced serotype-specific immunity and the age distribution of disease suggest that vaccine prevention is feasible.

Aedes aegypti control, even eradication, is technically feasible. However, given current financial and organizational constraints, successful mosquito control is not politically feasible.