Upon reviewing stakeholder concerns and scientific literature regarding the entire childhood immunization schedule, the IOM committee finds no evidence that the schedule is unsafe. The committee’s review did not reveal an evidence base suggesting that the U.S. childhood immunization schedule is linked to autoimmune diseases, asthma, hypersensitivity, seizures, child developmental disorders, learning or developmental disorders, or attention deficit or disruptive disorders.
Existing mechanisms to detect safety signals — including three major surveillance systems of FDA-approved products maintained by the CDC and a supplemental vaccine safety monitoring initiative by the FDA—provide further confidence that the current childhood immunization schedule is safe.
Despite the reassuring available evidence, the committee calls for continued study of the immunization schedule using existing data systems.
Answering research questions of the most importance to stakeholders could be done through a variety of methods. The committee does not endorse conducting a new randomized controlled clinical trial that would compare the health outcomes of unvaccinated children with their fully immunized peers. Although this is the strongest study design type, ethical concerns prohibit this study, as unvaccinated individuals and communities intentionally would be left vulnerable to morbidity and mortality. While stakeholder concerns should be one, but not the only, element that drives continued searches for scientific evidence, the committee writes that these concerns alone, absent epidemiological or biological plausibility of potential safety problems, do not warrant further study.
A new observational study, a complex undertaking that also would require a considerable investment, would be less likely than a randomized controlled clinical trial to conclusively reveal differences in health outcomes between children who are fully immunized and unimmunized children. Fewer than 1 percent of Americans refuse all immunizations. Enrolling sufficient numbers of unvaccinated children and matching them with vaccinated children of the same age, gender, ethnicity, and geographic location — a necessary step to rule out chance findings — would be prohibitively difficult and time-consuming.