Immunization against infectious disease.

Mortality and morbidity from infectious diseases in the United States have declined more than 90 percent since 1900. Factors believed to be responsible for this decline include changes in the natural history of disease, sanitation, quarantine measures, control of nonhuman vectors, antibacterial drugs, and immunization. The contributions of each of these factors differ among the various infectious diseases; except for smallpox and diphtheria control, immunization had little effect until after World War II. The success of present and future immunization programs is endangered by public and physician complacency and by complex legal and ethical problems related to informed consent and responsibility for rare, vaccine-related injury.