Funding for this research was provided by:
Nanjing Medical Science and Technique Development Foundation (QRX11038)
Nanjing Municipal Science and Technique Development Foundation (201715058)
Received: 17 October 2020
Accepted: 21 December 2020
First Online: 6 January 2021
Ethical approval and consent to participate
: Written informed consent was obtained from both schools and parents/guardians prior to the on-site survey. Academic and Ethics Committee of Nanjing Municipal Center for Disease Control and Prevention, China, reviewed and approved this study (2017006).
: The authors declare that they have no competing interests.