1. U.S. Science Envoy Program, Department of State and White House, Washington, DC 20520, USA; Sabin Vaccine Institute and Texas Children's Hospital Center for Vaccine Development, National School of Tropical Medicine, Baylor College of Medicine, Houston, TX 77030, USA; Department of Biology, Baylor University, Waco, TX 76706, USA; James A. Baker III Institute of Public Policy, Rice University, Houston, TX 77005, USA.