1. Department of Epidemiology, School of Public Health, Fudan University, Key Laboratory of Public Health Safety, Ministry of Education, Shanghai, China
2. Department of Infectious Diseases Prevention, Suzhou Center for Disease Prevention and Control, Suzhou, China
3. Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA, USA
4. Administrating office, Suzhou Center for Disease Control and Prevention, Suzhou, China