Text and Data Mining valid from 2019-12-01
Received: 21 January 2019
Accepted: 14 November 2019
First Online: 10 December 2019
Ethics approval and consent to participate
: The study protocol was reviewed and approved by the Ethical Review Commit-tee of China Center for disease control and prevention (Unique ID Number: 201821). Informed consent was waived as this was an analysis of anonymized routine surveillance data.
: Not applicable.
: The authors declare that they have no competing interests.