A review of the available evidence underscores the safety of the federal childhood immunization schedule, according to a report released today by the Institute of Medicine. University of Michigan population ecologist Pejman Rohani served on the 13-person committee that wrote the report.
Roughly 90 percent of American children receive most childhood vaccines advised by the federal immunization schedule by the time they enter kindergarten, the committee noted. However, some parents choose to spread out their children's immunizations over a different time frame than recommended by the schedule, and a small fraction object to having their children immunized at all.
Their concerns arise in part from the number of doses that children receive. The schedule entails 24 immunizations by age 2, given in amounts ranging from one to five injections during a pediatric visit.
"We reviewed the available data and concur with studies that have repeatedly shown the health benefits associated with the recommended schedule, including fewer illnesses, deaths and hospital stays," said Rohani, a professor of ecology and evolutionary biology, a professor of complex systems and a professor of epidemiology at the School of Public Health.
"Every new vaccine is tested for safety and evaluated in the context of the entire schedule before it is added. And the systems designed to detect possible harmful effects of immunization have worked well at discovering occasional problems with individual vaccines."
Until newer and bigger data collection systems can be harnessed, the Vaccine Safety Datalink (VSD) is the best available tool for exploring questions about the immunization schedule should the need arise, the committee concluded. This database contains information on the immunization histories of more than 9 million people covered by nine participating managed care organizations.
Researchers can identify individuals who were vaccinated according to alternative schedules as well as any diagnoses, medical procedures and outcomes they have experienced. VSD also contains data on race, age, gender and other factors that help researchers do better comparisons and account for factors that might affect participants' health. Already a research team has tapped VSD to explore patterns among children in the Kaiser Permanente Colorado system who are defined as under-vaccinated.
However, VSD tracks people from only eight states and looks at a smaller percentage of low-income and minority people than is in the U.S. population as a whole. Moreover, VSD's usefulness depends on the continuing involvement of participating health plans. The U.S. Department of Health and Human Services and its partners should maintain their commitment to funding VSD and consider bringing in additional health plan members to enhance the data and make it more representative of the full U.S. population, the report states.
Some critics of immunization policies have called for studies comparing health outcomes among vaccinated and unvaccinated children and for research to determine if subgroups exist that are predisposed to experiencing harmful health effects from the vaccines.