1. National Institute for Viral Disease Control and Prevention, China CDC, Beijing 100052, China
2. School of Basic Medical Sciences of Jilin University, Changchun 130021, China
3. Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
4. Centers for Disease Control and Prevention, Atlanta, Georgia
5. World Health Organization, Geneva, Switzerland
6. Hebei Province Center for Disease Control and Prevention, Lulong County, China