1. Center for Health Research, Kaiser Permanente Northwest, Portland, OR, USA
2. RTI Health Solutions, Research Triangle Park, NC, USA
3. Oregon Health and Science University, Portland, OR, USA
4. Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA, USA
5. Battelle Memorial Institute, Brookhaven, GA, USA
6. Division of Research, Kaiser Permanente Northern California, Oakland, CA, USA
7. Abt Associates, Inc., Cambridge, MA, USA