Newer systems, including the National Children's Study and the Post-Licensure Rapid Immunization Safety Monitoring (PRISM) program, could also provide useful information, according to the IOM authors.
The committee concluded that the best tool out of that group is the Vaccine Safety Datalink, which collects information on demographics, vaccination history, diagnoses, medical procedures, and outcomes from more than 9 million children and adults treated within nine managed care organizations.
Potential limitations of that data source, however, include a lower level of diversity in the study population when compared with the U.S. general population and potential difficulty in accounting for differences between children who adhere to the federal vaccine schedule and those who use an alternate schedule.
"Future federal research approaches should continue to fund and support the Vaccine Safety Datalink project to study the safety of the recommended immunization schedule," the authors wrote.
They ruled out randomized trials as a way to evaluate the safety of the vaccine schedule because, "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."
Also, because fewer than 1 percent of all Americans refuse all vaccines, an observational study to compare vaccinated and unvaccinated children would have to very large -- prohibitively so -- to find meaningful differences in health outcomes, according to the report.