1. Center for Infectious Disease Dynamics, Pennsylvania State University, State College, PA 16801, USA.
2. Fogarty International Center, National Institutes of Health, Bethesda, MD 20892, USA.
3. School of Public Health and Health Services, George Washington University, Washington, DC 20052, USA.
4. Healthcare Cost and Utilization Project, Center for Delivery, Organization and Markets, Agency for Healthcare Research and Quality, U.S. Department of Health and Human Services, Rockville, MD 20850, USA.
5. Epidemiology Branch, Division of Viral Diseases, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA.
6. Department of Ecology and Evolutionary Biology and Woodrow Wilson School, Princeton University, Princeton, NJ 08544, USA.