Immunization principles and vaccine use

Among the valid contraindications applicable to all vaccines are a history of anaphylaxis or other serious allergic reactions to a vaccine or vaccine component and the presence of a moderate or severe illness, with or without fever. Infants who develop encephalopathy within 72 h of a dose of DTP or DTaP should not receive further doses; those who experience a "precaution" event should not normally receive further doses. Because of theoretical risks to the fetus, pregnant women should not receive MMR or varicella vaccine.

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An illuminating example is the case of Rotashield, a rhesus reassortant rotavirus vaccine, which was introduced for routine use in the United States in the late 1990s. Within 9 months of its introduction, cases of intussusception were reported by the CDC to be temporally associated with the administration of the initial vaccine dose. This report led first to the cessation of the vaccine's use and subsequently to its withdrawal from the market and the discontinuation of its production.

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Current Controversies Even though vaccines are very safe and serious adverse events proven to be due to licensed vaccines are rare, the recent rise in the reporting of autism spectrum disorders has led some parents of affected children to claim that thimerosal—used as a preservative—is the cause of the problem. No study has yet implicated thimerosal or the vaccines in which it has been used as a likely cause of these disorders; however, fully 50% of cases before the Vaccine Injury Compensation Program concern autism allegedly due to mercury.

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Table 116-4 Standards for Immunization Practice Child and Adolescent Immunization Practice 1. Immunization services are readily available. 2. Vaccinations are coordinated with other health care services and provided in a "medical home" when possible. 3. Barriers to vaccination are identified and minimized. 4. Patient's costs are minimized. 5. Health care professionals review the vaccination and health status of patients at every encounter to determine which vaccines are indicated. 6. Health care professionals assess for and follow only medically accepted contraindications. 7.

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Table 116-3 Valid and Invalid Contraindications to Vaccination Vaccine Valid Contraindicationa Invalid Contraindication All vaccines in general Serious allergic Mild acute illness with reactions (e.g.

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Current recommendations also include influenza vaccine for routine annual administration to individuals with chronic illness at any age, to persons living in the same household as chronically ill individuals, and to all adults 50 years of age. Polyvalent pneumococcal polysaccharide vaccine is similarly recommended for adults ≥65 years of age and for all chronically ill persons.

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Principles of Vaccine Use Route of Administration Microbes differ in their routes of infection, patterns of transmission, and predispositions for certain age groups. The route of vaccine administration (oral, intranasal, intradermal, transdermal, subcutaneous, or intramuscular) takes these factors into account in order to maximize protection and minimize adverse events. Vaccine development is more a pragmatic undertaking than an exact science, guided only in part by immunologic principles and shaped largely by the results of clinical trials.

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As noted above, the number of licensed vaccines and the strategies for their best use change constantly as new products, new indications, and new information become available. The Advisory Committee on Immunization Practices (ACIP) regularly amends immunization recommendations to reflect the evolution of vaccines and vaccination policy in the United States.

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For common and highly communicable childhood diseases such as measles, the target population is the universe of susceptible individuals, and the time to immunize is as early in life as is feasible and effective.

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Risk Assessment Vaccines are considered safe when the risk of use is judged to be acceptable in relation to the benefits. For vaccines given to healthy individuals for diseases that are no longer common, acceptable risks are set at very low levels—indeed, far lower than for most medical products. However, "safety" does not and cannot ever mean "zero risk." The determination of safety is thus based on a scientific assessment of the data and a considered judgment of all the issues involved, including benefits and risks.

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Approaches to Passive Immunization Passive immunization is generally used to provide temporary immunity in a person exposed to an infectious disease who has not been actively immunized; this situation can arise when active immunization is unavailable (e.g., for respiratory syncytial virus) or when active immunization simply has not been implemented before exposure (e.g., for rabies). Passive immunization is used in the treatment of certain illnesses associated with toxins (e.g.

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Harrison's Internal Medicine Chapter 116. Immunization Principles and Vaccine Use Principles of Immunization The immune system, composed of a variety of cell types and soluble factors, is geared toward the recognition of and response to "foreign" substances termed antigens. Vaccines convey antigens from living or killed microorganisms (or protein or carbohydrate molecules derived from these antigens) to elicit immune responses that are generally protective but can occasionally backfire and cause harm to the recipient.

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The Immune Response While many constituents of infectious microorganisms and their products (e.g., exotoxins) are or can be rendered immunogenic, only some stimulate protective immune responses that can prevent infection and/or clinical illness or (as in the case of rotavirus) can attenuate illness, providing protection against severe disease but not against infection or mild illness. The immune system is complex, and many factors—including antigen composition and presentation as well as host characteristics—are critical for stimulation of the desired immune responses (Chap. 308).

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