Funding for this research was provided by:
Sichuan Science and Technology Program (2020YFS0001, 2021YJ0140)
Received: 8 March 2021
Accepted: 24 September 2021
First Online: 3 October 2021
: Because this study constituted public health surveillance rather than research in human beings, ethics approval was not available after consulted to the ethics committees of Sichuan Center for Disease Control and Prevention. And data collected from participants in this study are required following the Law of the People’s Republic of China on the Prevention and Treatment of Infectious Diseases. We also did not include any data of patients’ personal information and therefore written informed consent was not required [CitationRef removed]. The access to raw data was granted by Changhong Yang.
: Not applicable.
: The authors declare that they have no competing interests.