1. National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, State Key Laboratory for Infectious Disease Prevention and Control, Beijing 102206, China
2. Jiangsu Provincial Centre for Disease Control and Prevention, Nanjing 210009, China
3. National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing 100052, China
4. Xuzhou Municipal Centre for Disease Control and Prevention, Xuzhou 221006, China
5. Sichuan Provincial Centre for Disease Control and Prevention, Chengdu 610041, China
6. Nantong Municipal Centre for Disease Control and Prevention, Nantong 226006, China