Received: 6 July 2018
Accepted: 1 March 2019
First Online: 11 March 2019
Ethics approval and consent to participate
: This research was carried out according to the principles of the Declaration of Helsinki and was approved by the Ethics Committees of the National Institute for Communicable Disease Control and Prevention and the Chinese Center for Disease Control and Prevention (No.ICDC-2014005). The subjects consented to participate and no animal work was carried out as part of this study.
: Parental written informed consent to publish this information was obtained from study participants.
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