and editorials. The committee used medical subject heading searches to identify references, using the terms “immunization” (which includes “immunization schedule”), “vaccines,” “attitude to health,” and “attitude of health personnel.”

The initial literature search yielded 421 articles. To further refine the search, the committee reviewed the titles and abstracts (when available) and removed articles that met any of following three exclusionary criteria. First, from the beginning of the study period, the committee noted that the childhood immunization schedule spans the entire period of childhood (birth to age 18 years). The committee found that the most prominent safety concerns about the immunization schedule are related to vaccinations received during infancy and early childhood. Thus, the committee focused its review on the body of literature that addressed concerns about the short- and long-term effects of the schedule of vaccinations given to young children (birth to age 6 years) and excluded studies that focused on the immunization schedule for older children and adolescents (age >6 years). Second, the committee excluded studies that focused on individual vaccines or combination immunizations rather than the entire childhood immunization schedule. Finally, the committee excluded studies of non-U.S. populations, unless the study focused on the U.S. Advisory Committee on Immunization Practices (ACIP)–recommended immunization schedule for young children.

After the committee applied these criteria, it retained 85 published articles for comprehensive review. Two-thirds of these articles were categorized as studies of parental concerns about either safety (n = 26) or communication between providers, public health authorities, and parents (n = 31). Several articles that the committee reviewed did not meet the study criteria (largely owing to having an older publication date) but were frequently cited in the literature and added to the committee’s knowledge base.

An iterative review of the literature as well as oral and written public comments revealed that among the primary stakeholders (parents, health care providers, public health officials), a subset of parents were the group with the most concerns about the safety of the immunization schedule. The review also revealed that parents, providers, and public health officials all believe that effective communication about these safety concerns remains a challenge.


Parental concerns about the safety of vaccines and the immunization schedule have been well publicized but are not well understood by all health care professionals. A number of recent studies have described the challenges associated with research into the safety of the immunization schedule and defined the methods that can be used to elicit and quantify parental concerns

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