The complexity of the current immunization schedule, which includes variables such as the number of doses, the age of administration, and the time between doses, permits the examination of a large number of potential research questions. Nevertheless, the committee noted a general lack of consistent and integrated theories of biological mechanisms or pathways that link specific elements of the immunization schedule to specific health conditions in the vaccinated child.

Perhaps the most compelling hypothesis is that introduction of an excess of immune-stimulating agents into an immature or dysregulated immune system might result in a cascade of adverse immunological processes culminating in asthma, allergies, autoimmune disorders, and the like. Nevertheless, the biological evidence to support this line of reasoning was examined by an Institute of Medicine committee in 2002 as part of the Immunization Safety Review series, and that examination found no more than weak justification for such a hypothesis (IOM, 2002).

Likewise, the committee’s review of existing epidemiological studies of the immunization schedule was complicated by the effectively infinite number of variations for delivery of the recommended childhood immunization schedule that could be investigated. The literature summarized in Chapter 5 reflects the range of approaches that have been used to characterize departures from the recommended schedule, and no single approach prevailed across multiple investigations.

The committee struggled in its efforts to identify research questions that could be posed to evaluate the health outcomes after immunization with the recommended childhood immunization schedule because of a lack of well-defined exposures and biologically plausible outcomes. Thus, the primary research questions of interest that the committee identified and that are listed below are broad and most likely too general to be readily translated into new research studies, unless biologically plausible hypotheses emerge.

Among the many questions about the current immunization schedule that could be posed, the committee identified what it viewed to be the leading research questions of interest on the basis of a review of stakeholder concerns. The committee parsed the phrase “this question” in Part 2 of the statement of task into four broad research questions. These questions are listed in Box 6-1.

The committee identified other potential gaps in research on the larger health care delivery system and policy-setting procedures that influence parents’ knowledge of and decisions about their immunization choices for their children. For example, several stakeholders identified the need for additional research on effective provider-patient communications on the risks and benefits of vaccinations. Others suggested the value of additional re-search

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