Measles is an extremely contagious viral illness that causes 2.5 million child deaths worldwide per year. Encephalitis strikes approximately one in 1000 measles victims and results in 15% mortality; 25% to 35% of the survivors suffer permanent neurological impairment. Rubella is another highly contagious childhood disease. Its effects are usually mild; yet this virus causes encephalitis, deafness, retardation, and other congenital defects in children whose mothers were infected during pregnancy, especially in the first trimester.
Both of these infections are rampant throughout most of the world, although their impact has been dramatically reduced in many industrialized nations in the past two decades, largely because of the implementation of effective immunization programs. In 1978, the Public Health Service called for the elimination of indigenous measles from the United States by 1982. Although this goal was not achieved, striking declines in the incidence of measles, rubella, and the congenital-rubella syndrome have occurred.