Although mumps, an acute infectious disease, is not usually serious, rare and dangerous complications can occur. These include encephalitis, meningoencephalitis, and damage to the inner ear which leads to deafness. Children from age 5 to 15 are most susceptible.
Only 30 cases of mumps were reported in the USA in 1993. The sharp drop in the incidence of the disease since 1990 is attributed to immunization programmes, especially among pre-school children.