News & Views: IOM Reviews Safety of Childhood Vaccine Schedule

Historically, the Institute of Medicine (IOM) has convened groups to review a variety of vaccine-related issues, including vaccine safety concerns. In each case a committee of experts was charged with offering “independent, objective, evidence-based advice” meant to inform the direction of policy and provide a viewpoint based on the compendium of existing information for the public and private sectors. Most recently, the IOM turned its attention to concerns about the safety of the childhood immunization schedule. The resulting report, “The Childhood Immunization Schedule and Safety: Stakeholder Concerns, Scientific Evidence, and Future Studies,” was released on January 16, 2013.

The committee and its charge

The 14-member committee was charged with:

• Reviewing existing literature and stakeholder’s concerns related to the safety of the recommended immunization schedule
• Identifying appropriate methodological approaches for determining the safety of said schedule
• Issuing a summary report

To compile the report, committee members participated in three information-gathering sessions and five committee meetings, completed an extensive literature review, commissioned a paper about study designs, and reviewed approximately 900 public comments.

The resulting approximately 200-page report provides background information about both the study and the immunization schedule (chapters 1 and 2), reviews existing systems for data collection and existing literature (chapters 3 and 5), discusses stakeholder concerns (chapter 4), and reviews methodological approach options as well as feasibility, ethical issues, and priorities as they relate to questions about the current schedule (chapter 6). The final chapter (chapter 7), a report summary and an abstract outline the conclusions of the committee.

Stakeholder concerns

Conclusions were based on three primary sources of information including the current scientific literature, online comments and public testimony. A subset of parents was found to be the stakeholder group with the most concerns about the safety of the immunization schedule. Their concerns focused on overloading the child’s immune system, lack of data in the literature, specifically regarding individual susceptibilities that may make a child more likely to experience negative outcomes, and communication of existing data in response to these fears. Outside influences were also identified, particularly in the online comments and the public testimony, suggesting that parental decisions are also affected by skepticism relating to the quality of research and untoward influence by pharmaceutical companies and governmental groups that oversee research.

Concerns related to effectively communicating vaccine safety among stakeholders were indicated by a larger subgroup that included not only parents, but also providers and public health officials. In addition, while the latter groups did not indicate concerns about the safety of the immunization schedule, providers did indicate a need for more information related to vaccine delivery and communication surrounding the schedule.

Existing literature related to the schedule

The committee determined the scientific literature to be lacking in three areas:

• Elements of the immunization schedule, such as number, frequency, timing, order and age at receipt
• Health outcomes related to vaccine safety (i.e., the “completeness” of the list of conditions studied)
• Outcomes specific to particular subpopulations

The committee felt that standardizing definitions related to these areas would improve the quality of future studies.

Methodological approaches

Four broad research questions relating to concerns about the safety of the immunization schedule were defined:

• “How do child health outcomes compare between those who receive no vaccinations and those who receive the full currently recommended immunization schedule?”
• “How do child health outcomes compare between (a) those who receive the full currently recommended immunization schedule and (b) those who omit specific vaccines?”
• “For children who receive the currently recommended immunization schedule, do short- or long-term health outcomes differ for those who receive fewer immunizations per visit (e.g., when immunizations are spread out over multiple occasions)?”
• “Do potentially susceptible subpopulations (for example, children from families with a history of allergies or autoimmune diseases) who may experience adverse health consequences in association with immunization with the currently recommended immunization schedule exist?”

A variety of methodological approaches were reviewed for the appropriateness of answering these questions including randomized controlled trials, observational studies, secondary analysis of existing databases, and animal models. While randomized controlled trials were considered the gold standard, the report discussed reasons they were not an appropriate approach for the aforementioned questions. The Vaccine Safety Datalink (VSD) was described as one of the current best systems for gathering information via a secondary analysis, and enhancements were suggested to make this a more robust option.

After review of presentations, sources of data, the commissioned report and the literature, the committee suggested an approach in which concerns of stakeholders are identified and decisions to begin studies are then based upon the following:

• Epidemiological evidence for an association of the concern with elements of the immunization schedule
• Biological plausibility of the concern

The committee also commented on the oft-suggested “vaccinated versus unvaccinated” study recommending against such a study based on factors that included:

• The large study size needed to aptly power the findings of such rare events would be difficult to obtain.
• Any study based on naturally occurring unimmunized populations (e.g., religious groups) would be fraught with confounding variables.
• Randomly assigning children to be members of the “unimmunized” group would be unethical.

Conclusions of the committee

The conclusions of the report described a lack of evidence to support the safety concerns purported by stakeholders, but a realization that perceptions must also be addressed. In this light, the committee called for future studies to address the full scope of the schedule as well as the commencement of studies to better understand perceptions and how they are formed. Further, while concerns of stakeholders should be acknowledged and serve as a potential source for scientific questions, existing evidence and biological plausibility should inform the decision to begin scientific studies. The committee further concluded that evidence does not suggest that the current immunization schedule is unsafe.

Potential for applications in practice

The IOM report can serve as evidence that parents’ concerns related to the immunization schedule are being addressed, and that when an extensive review was completed, the conclusion was that the current schedule is safe. Further, while the committee pointed to the fact that evidence looking at the elements of the schedule is not as plentiful as we may wish, the reality is that this indicates even less knowledge about the effects of altering the schedule.

The framework suggested by the committee can also provide a basis for discussions about how the scientific community addresses parental concerns about vaccine safety. That is to say, if a concern is brought about, the existing evidence and biological plausibility should be assessed and if appropriate, sound scientific studies should follow.

Finally, the discussion of the “vaccinated versus unvaccinated” study provided in this report should provide support when discussing this notion with parents who deem such a study plausible.

More information

• Access the report in its entirety (free)
• Dr. Offit’s Medscape Video about the IOM report
• Recommended Immunization Schedule: What you should know
  • English [PDF, 611KB]
  • Spanish [PDF, 741KB]
• Additional information about the immunization schedule