1. Sten H. Vermund is at the Vanderbilt Institute for Global Health and Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, TN 37203, USA.
2. K.M. Venkat Narayan is in the Departments of Global Health and Epidemiology, Rollins School of Public Health, Emory University, Atlanta, GA 30322, USA.
3. Roger I. Glass is in the Fogarty International Center, National Institutes of Health, Bethesda, MD 20892, USA.