Received: 13 October 2020
Accepted: 18 January 2021
First Online: 19 February 2021
Ethics approval and consent to participate
: The study was approved by Ethics Committee of Sichuan CDC (SCCDCIRB-2020-021) and was conducted in agreement with the Declaration of Helsinki. <i>Informed consent</i> was obtained from all individual participants including the underage permitted by their parents/guardians.
: Not applicable.
: All authors declare no conflicts of interests.