I researched articles that discussed the effects of vitamins and minerals on SARS-COV-2, coronavirus, Influenza as well as other viruses that cause upper respiratory infections. Here is my summery in the video below.
I researched some foods that can provide these vitamins. I think it is possible to build our immune system by nutrition and some supplementation.
If you cant find Zinc or Selenium pills get the food rich in it.
Ref for zinc: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3273967/
Ref for Selenium: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3723386/