1. Department of Epidemiology, Ministry of Education Key Laboratory of Public Health Safety, Fudan University School of Public Health, Shanghai, China
2. Department of Immunization Planning, Minhang District Center for Disease Control and Prevention, Shanghai, China
3. Minhang Branch, Fudan University School of Public Health, Shanghai, China
4. Department of Epidemiology, University of Michigan, Ann Arbor, MI, USA