1. Department of Laboratorial Science and Technology & Vaccine Research Center, School of Public Health, Peking University, Beijing 100191, China
2. Center for Infectious Diseases and Policy Research & Global Health and Infectious Diseases Group, Peking University, Beijing 100191, China
3. Key Laboratory of Epidemiology of Major Diseases (Peking University), Ministry of Education, Beijing 100191, China
4. Department of Epidemiology, School of Public Health, University of Pittsburgh, Pittsburgh, PA 15260, USA
5. Jiuzhaigou Center for Disease Control and Prevention, Ngawa 623099, China
6. Yilan Center for Disease Control and Prevention, Harbin 154899, China
7. Longxi Center for Disease Control and Prevention, Longxi 748199, China
8. Chengguan Center for Disease Control and Prevention, Lanzhou 730030, China
9. Suzhou Center for Disease Control and Prevention, Suzhou 234099, China