Immunization

Immunizations can partially or completely prevent illness by a specific microorganism. By preventing illness, immunizations avert the acute effects of disease, complications of disease, and long-term disability related to disease. When immunizations are widely used, the spread of disease within the population can also be prevented. By preventing outbreaks of disease, immunizations reduce health-care expenditures, including the costs of: (1) prescription and over-the-counter medications, (2) health-care provider visits (including office and emergency room visits), (3) hospitalization, and (4) long-term disability or long-term care. Immunizations also save money by reducing the number of days of work loss by employees because of personal illness or illness in a dependent family member.

Immunizations can provide active or passive protection against an infectious disease. In active immunization, entire organisms (e.g., inactivated bacteria; live, weakened virus) or their parts (e.g., bacterial toxoid; inactivated, viral antigen) are administered. The immune system responds to the vaccine by producing a long-lasting, protective immune response in the recipient. Examples of active immunization include all of the vaccines used in the standard childhood immunization schedule (see Table 1). In passive immunization, preformed antibodies against specific microorganisms are administered. Protection lasts only months because of the relatively short half-life of the antibodies. Passive immunization is used before or immediately after an exposure to an infectious agent to prevent infection. Passive immunization is used for a number of infectious agents, including hepatitis B, rabies, respiratory syncitial virus, tetanus, and varicella-zoster. The remainder of this discussion will be directed toward active immunizations used during childhood.

Immunizations can be recommended on either a universal or a selective basis. Universal immunizations are directed at all members of a population. The eventual goal of immunizing all susceptible individuals is the complete eradication of a disease, as in the case of smallpox. Selective immunizations are directed at individuals who are considered at high risk of a disease, or at high risk of complications of a disease.

In the United States, the choice and timing of immunizations are made jointly by three national organizations—the Advisory Committee on Immunization Practices branch of the federal government's Centers for Disease Control and Prevention, the Committee on Infectious Diseases of the American Academy of Pediatrics, and the American Academy of Family Physicians. The complete schedule for universal immunizations is updated and published annually (see Table 1). Alterations to the schedule (e.g., addition of newly approved vaccines and changes in the timing of vaccines) can nevertheless be made throughout the year.