traditional public health model—in which each vaccine can confer long-lasting, often lifetime, protection against a specific physical disease. Currently, infants and children can and should be immunized against poliomyelitis, diphtheria, pertussis, tetanus, measles, mumps, rubella, Haemophilus influenzae type b (Hib) to protect children from meningitis, and hepatitis B. For example, when children are not immunized for Hib and meningitis occurs, there is the possibility of long-term negative effects on the brain, resulting in neurodevelopmental problems, mental retardation, learning disability, and psychological and behavioral disorders (Plotkin and Mortimer, 1988).

In the United States, widespread vaccination on appropriate schedules has produced a dramatic drop in the number of cases of the previously common childhood diseases, and their associated high mortality, morbidity, and sequelae. These declines are reported at 97 percent or more since the year the maximum number of cases for each disease was reported (Peter, 1992).

The cost-effectiveness of vaccination is well documented (Hinman, 1988). In 1983 the measles-mumps-rubella vaccine program had a cost-benefit ratio of 14:1, leading to a total saving of $1.4 billion (White, Koplan, and Orenstein, 1985). A study of pertussis vaccine showed that $2.10 is saved for each $1.00 spent on pertussis vaccination (Hinman and Koplan, 1985).

Currently, there is an immunization crisis in the United States, signaled by recurrent measles epidemics. Because measles is the most contagious of the vaccine-preventable diseases, its resurgence acts as a sentinel that warns of a breakdown in the overall immunization rates for other diseases. Epidemiological studies find that the source of the problem lies in the failure to achieve adequate immunization rates among children in the first two years of life. Rates are well below the 1990 national objective of 90 percent of children with completed immunizations by the second birthday (Cutts, Zell, Mason, Bernier, Dini, and Orestein, 1992; CDC, 1991). The failures of preschool immunization are most notable in inner-city and minority populations. In the inner-city areas, typically, fewer than 50 percent of the two-year-olds have been appropriately vaccinated, and African-American and Hispanic children are at highest risk (CDC, 1992, 1991, 1990).

In 1991 the National Vaccine Advisory Committee identified four major reasons for the low immunization rates among preschool children: (1) missed opportunities for vaccination, (2) deficiencies in the public health care delivery system, (3) lack of access to care, and (4) inadequate public awareness of the importance of immunizations. To ensure that immunizations reach all high-risk groups, specially de-



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