of the immunization schedule, certain enhancements to the research infrastructure will be needed, as detailed in Chapter 6.

The committee recognizes that the establishment of priorities for research will be a challenge. Thus, the committee proposes a process for setting priorities that recognizes stakeholder concerns and establishes these priorities on the basis of epidemiological and other evidence (based on formal systematic reviews), biological plausibility, and feasibility.

Before the U.S. Department of Health and Human Services (HHS) initiates further research on the entire immunization schedule through its agencies—most notably CDC, FDA, the National Institutes of Health, and NVPO—the biological plausibility of the association of a particular outcome with an aspect of the immunization schedule must be thoroughly reviewed. Along these lines, previous IOM vaccine safety committees have assessed the mechanisms by which vaccines potentially cause adverse events by identifying and evaluating the clinical and biological evidence (from human, animal, and in vitro studies) for individual vaccines. Furthermore, the recent IOM Committee to Review Adverse Effects of Vaccines developed categories for a mechanistic assessment of the weight of the evidence. Each assessment considers clinical information from case reports and clinical and experimental evidence from other sources (IOM, 2012).

Recommendation 6-1: The committee recommends that the Department of Health and Human Services incorporate study of the safety of the overall childhood immunization schedule into its processes for setting priorities for research, recognizing stakeholder concerns, and establishing the priorities on the basis of epidemiological evidence, biological plausibility, and feasibility.

The decision to initiate further studies should be based on an evaluation of three considerations that the committee identified through its review of stakeholder concerns and scientific findings:

  1. epidemiological evidence of potential adverse health outcomes associated with elements of the immunization schedule (such as postmarketing signals or indications of elevated risk from observational studies);
  2. biological plausibility supporting hypotheses linking specific aspects of the immunization schedule with particular adverse health outcomes; and
  3. concern about the immunization schedule’s safety expressed by stakeholders, which should initiate efforts to explore the two previous considerations.


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