A review of the available evidence underscores the safety of the federal childhood immunization schedule, says a new report from the Institute of Medicine. However, the report offers a framework for conducting safety research using existing or new data collection systems. should signals indicate the need for investigation of the schedule.

Roughly 90 percent of American children receive most childhood vaccines advised by the federal immunization schedule by the time they enter kindergarten. However, some parents choose to spread out their children's immunizations over a different time frame than recommended by the schedule.

Studies have repeatedly shown the health benefits associated with the recommended schedule, including fewer illnesses, deaths, and hospital stays, the report notes. 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, such as a rare intestinal disorder linked to a now-discontinued rotavirus vaccine. However, the elements of the schedule—the number, frequency, timing, order, and age at which vaccines are given—are not well-defined in existing research and should be improved.

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, according to the report. 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 (HHS) 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 says.

Newer data collection and surveillance systems offer great potential to monitor rare adverse events that may be associated with the childhood immunization schedule, the report said. When fully implemented, the Sentinel Initiative program being developed by the U.S. Food and Drug Administration (FDA) to monitor the safety of approved drugs and other medical products will complement existing passive vaccine surveillance systems, the report says. FDA's new Post-License Rapid Immunization Safety Monitoring Program is amassing a large amount of health data, offering the potential to analyze vaccine exposures and adverse events with a greater degree of statistical power.

The report was sponsored by HHS.