1. Department of Population Medicine, Harvard Medical School and Harvard Pilgrim Health Care Institute, Boston, Massachusetts;
2. Division of Research, Kaiser Permanente, Oakland, California;
3. Kaiser Permanente Vaccine Study Center, Oakland, California;
4. Immunization Safety Office, Centers for Disease Control and Prevention, Atlanta, Georgia;
5. Marshfield Clinic Research Foundation, Marshfield, Wisconsin; and
6. Kaiser Permanente Center for Health Research, Portland, Oregon