Funding for this research was provided by:
National Natural Science Foundation of China (71573095)
Bill and Melinda Gates Foundation (51914)
Text and Data Mining valid from 2019-08-02
Received: 8 September 2018
Accepted: 9 July 2019
First Online: 2 August 2019
Ethics approval and consent to participate
: Ethical permission was obtained from the Institutional Ethics Committee, Chinese Center for Disease Control and Prevention, China (No. 201626).
: Not applicable.
: The authors declare that they have no competing interests.