Major impediments to measles elimination. The modern epidemiology of an ancient disease.

Great success has been achieved in controlling measles in the United States with a greater than 99% reduction in incidence rate from the prevaccine era. However, since 1981, the incidence rate of measles in the United States has been relatively stable at approximately 1,500 to 3,000 reported cases annually. We reviewed available information to determine the remaining impediments to elimination of measles. The potential impediments can be divided into two categories: (1) implementation of the current strategy and (2) whether the current strategy needs modification. The major reason for the failure to achieve elimination appears to be the fact that some persons for whom vaccine is indicated have not been vaccinated. While vaccine failures and importations play a role in transmission, sustained transmission in a totally vaccinated community has not been demonstrated. All chains of transmission have involved some unvaccinated persons. Measles elimination will require complete implementation of current strategies and careful monitoring of epidemiologic trends to determine whether future modifications in strategy are needed.