Selenium has important roles including in the glutathione antioxidant pathways, and has roles in immune function.
Selenium, Selenoproteins, and Immunity
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6163284/
It is low in some Chinese populations and high enough to be toxic in others
Wuhan is not listed in the high risk areas
The Changing Selenium Nutritional Status of Chinese Residents
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3967180/