1. Center for Health Studies, Group Health Cooperative, Seattle, Washington
2. Departments of Pediatrics and Epidemiology, University of Washington Schools of Medicine and Public Health, Seattle, Washington
3. Kaiser Foundation Hospital, Panorama City, California
4. Division of Epidemiology, Office of Biostatistics and Epidemiology, Center for Biologics Evaluation and Research, Food and Drug Administration, Rockville, Maryland
5. National Immunization Program, Centers for Disease Control and Prevention, Atlanta, Georgia
6. Pediatric Vaccine Study Center, Northern California Kaiser Permanente, Oakland, California
7. Center for Health Research, Northwest Kaiser Permanente, Portland, Oregon
8. Department of Preventive Care, Group Health Cooperative, Seattle, Washington