Funding for this research was provided by:
National Natural Science Foundation of China (81772154)
Received: 10 November 2018
Accepted: 9 January 2019
First Online: 24 January 2019
Ethics approval and consent to participate
: This study was approved by the Research Ethics Committee of the National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, the Research Ethics Committee of the Beijing Centers for Disease Control and Prevention, and the Research Ethics Committee of the Beijing Children’s Hospital.
: Not applicable.
: The authors declare that they have no competing interests.
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