1. Department of Expanded Program on Immunization, Lu’an Municipal Center for Disease Control and Prevention, Lu’an, Anhui, China
2. Department of Expanded Program on Immunization, Huoshan County Center for Disease Control and Prevention, Lu’an, Anhui, China
3. Department of Expanded Program on Immunization, Huoqiu County Center for Disease Control and Prevention, Lu’an, Anhui, China
4. Department of Epidemiology and Health Statistics, School of Public Health, Anhui Medical University, Hefei, Anhui, China