1. Department of Epidemiology and Health Statistics, School of Public Health, Anhui Medical University, Hefei, Anhui, China
2. Department of Expanded Program on Immunization, Lu’an Municipal Center for Disease Control and Prevention, Lu’an, Anhui, China
3. Department of Health Inspection and Quarantine, School of Public Health, Anhui Medical University, Hefei, Anhui, China
4. Marketing Center, China Biotechnology Corporation, Beijing, China