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Vaccines represent one of the most successful public health interventions of all time. Diseases that once killed thousands of children each year have been virtually eliminated from the United States (Table 3–1). Because vaccines have been so effective, many parents and younger physicians have little firsthand experience with the infectious diseases they prevent. In this context, attention has shifted away from concerns of vaccine-preventable diseases themselves toward concerns of vaccine safety, both perceived and real.

Table 3–1. Impact of Vaccines in the Twentieth Century

Figure 3–1 graphically depicts what may occur if the public loses faith in the immunization system. Disease incidence begins to decline when a new vaccine is introduced. If there is loss of confidence in the vaccine among a critical proportion of the population, outbreaks may occur. Continued decrease in disease incidence with potential disease eradication can only occur if public confidence in the vaccine program is restored.

Figure 3–1.

Life cycle of an immunization program.

There are several historical examples of what may occur when immunization practices suddenly shift. For instance, the incidence of pertussis was found to be 10–100 times lower in countries that maintained high levels of whole-cell diphtheria–tetanus–pertussis (DTP) vaccination in the 1980s as compared to countries with prominent anti-DTP movements.1 In Japan during the mid-1990s, immunizations were made optional after the occurrence of rare case reports of aseptic meningitis associated with measles–mumps–rubella (MMR) receipt. Consequently, measles made a recurrence, resulting in more than 100,000 cases and 50–100 deaths per year.2

Even in the United States, where many parents feel that there is no risk for infectious diseases, outbreaks have occurred when individuals are unvaccinated. These outbreaks are more likely to occur in clusters of vaccine-resistant communities.3 For example, in Colorado there were 14 measles outbreaks between 1987 and 1998.4 Children who were exempted from vaccination were 22 times more likely to acquire measles as children who were vaccinated. Another outbreak occurred in Indiana in the summer of 2005 when 34 members of a church acquired measles after an unvaccinated member returned from a missionary trip to Romania. 32 of the 34 affected individuals were unvaccinated, primarily due to concerns of vaccine safety.5 As the number of unvaccinated individuals increases, the potential for a large-scale outbreak in the United States becomes greater. ...

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