Funding for this research was provided by:
National Major S & T Research Projects for the Control and Prevention of Major Infectious Diseases in China (2017ZX10103004-004, 2018ZX10003006-001-004, 2018ZX10305409-001-004)
Received: 28 October 2019
Accepted: 11 June 2020
First Online: 16 June 2020
Ethics approval and consent to participate
: This study was performed in strict accordance with the human subject protection guidance of Ministry of Science and Technology of China, and the study protocol was approved by the Ethical Review Committee of Beijing Children’s Hospital with judgment’s reference number 2015–47. Written consent was obtained from the parents or guardians of all participants before data collection.
: Not applicable.
: The authors have no potential conflicts of interest.