1 Institute of Infectious Disease and Vaccine, School of Public Health, Zhejiang Chinese Medical University, Hangzhou, China.
2 Yinzhou District Center for Disease Control and Prevention, Ningbo, Zhejiang, China.
3 Yichang Municipal Center for Disease Control and Prevention, Hubei, China.
4 Institute of Infectious Disease and Vaccine, School of Public Health, Zhejiang Chinese Medical University, Hangzhou, China. Electronic address: fuchuanxi@zcmu.edu.cn.