families, children, and so forth that are affected by the immunization schedule cannot be ignored.


On June 2, 2009, the National Vaccine Advisory Committee (NVAC) reviewed the nation’s vaccine safety system and endorsed the recommendation of the NVAC Safety Working Group for an external expert committee, such as a committee convened by the Institute of Medicine (IOM), “with broad expertise in research methodologies, study design, and the ethical conduct of research to consider the strengths and weaknesses, ethical issues and feasibility including timelines and cost of various study designs to examine outcomes in unvaccinated, vaccine-delayed and vaccinated children and report back to the NVAC” (CDC, 2011b, p. 72).

The recommendation by the NVAC Safety Working Group was based on a series of meetings and discussions on the U.S. childhood immunization schedule in which individuals raised concerns that the schedule could potentially harm children because of immunological or neurodevelopmental adverse effects. Furthermore, in the minds of some parents, concerns about potential harms outweigh the well-documented benefits of immunization for the prevention of morbidity and mortality, with the result being that their children are less than fully immunized (NVAC, 2009).

After years of debate, some people continue to advocate for a study to compare health outcomes among vaccinated and unvaccinated children. The NVAC report stated that “the strongest study design, a randomized clinical trial that includes a study arm receiving no vaccine or vaccine not given in accord with the current recommended schedule, is not ethical, would not pass Institutional Review Board (IRB) review, and cannot be done” (NVAC, 2009, p. 38). (Chapter 6 discusses some of the ethical considerations in detail.) Furthermore, it may be impossible to draw unbiased results from an observational study of this issue because of potential differences in baseline health and social characteristics of populations and subgroups.


The National Vaccine Program Office of HHS asked the IOM to convene a diverse committee of experts in pediatrics, neurology, medical ethics, immunology, statistics, epidemiology, and public health to identify study designs feasible to address questions about the safety of the United States’ childhood immunization schedule. A 14-member committee was selected to

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