1. State Key Laboratory of Infectious Disease Prevention and Control, National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Changping, Beijing, China
2. Department of Epidemiology, School of Public Health, Shanxi Medical University, Taiyuan, Shanxi Province, China
3. Institute of Public Health, Nankai University, Tianjin, China
4. Department of Laboratorial Science and Technology & Vaccine Research Center, School of Public Health, Peking University, Beijing, China