1. From the Division of Research and the Vaccine Study Center, Kaiser Permanente, Oakland, California;
2. Department of Ambulatory Care and Prevention, Harvard Pilgrim Health Care and Harvard Medical School, Boston, Massachusetts, Pediatric Clinical Effectiveness Program, Children's Hospital, Boston, Massachusetts, and Department of Health Policy and Management, Harvard School of Public Health, Boston, Massachusetts; and the
3. Center for Health Studies, Group Health Cooperative, Seattle, Washington;
4. National Immunization Program, Centers for Disease Control and Prevention, Atlanta, Georgia.