The next section focuses on research questions that directly address the individual health benefits and risks of the recommended immunization schedule for the vaccinated child and describes a number of research approaches that could be pursued. The chapter then highlights the critical point that the consequences of individual vaccination choices can be considered only in light of the level of immunization in the larger population, to which the individual is invariably linked.

The committee recognized the vital importance of considering the population health impacts of any studies of the childhood immunization schedule. As the immunization schedule exists within a complex system consisting of individual-level protection and community immunity, studies that require any variations to the immunization schedule may have a profound impact on broader population health. After the discussion of methods to study individual health outcomes, the committee describes methods to monitor and maintain community immunity.


Each of the primary research questions of interest to stakeholders concerned about the safety of the immunization schedule described in Box 6-1 could be investigated by a range of study methods that vary considerably according to their cost, feasibility, and ethical propriety. At the one end are secondary analyses of existing data sets that could be initiated immediately; at the other end are primary research efforts involving the collection of new data, most notably, large, new RCTs.

This section describes the range of research approaches that could be pursued to investigate the leading questions of interest, with attention given to each approach’s potential according to cost, feasibility, and anticipated scientific yield and utility. The research strategies broadly include

  • initiation of new RCTs,
  • initiation of new observational studies, and
  • secondary analyses of data from current vaccine safety surveillance systems in the United States (such as VSD) and comparable international systems.

Each of these approaches has some potential to advance knowledge of the four primary research questions identified. The following sections discuss the strengths, limitations, cost, and feasibility of each approach.

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