1. Centers for Disease Control & Prevention; Atlanta GA USA
2. Marshfield Clinic Research Foundation; Marshfield WI USA
3. Kaiser Permanente Vaccine Study Center; Oakland CA USA
4. Department of Research and Evaluation; Kaiser Permanente Southern California; Pasadena CA USA
5. Group Health Research Institute; Seattle WA USA
6. Institute for Health Research; Kaiser Permanente; Denver CO USA
7. Center for Health Research; Kaiser Permanente Northwest; Portland OR USA