Iron. There is research going on about iron chelation being an effective part of Covid treatment. That is because iron feeds any infection. They are using medication (which can have side effects).
Other ways to reduce iron I have found effective include avoiding beef and eating Bragg ACV, cabbage, lactoferrin, turmeric, green tea, IP6, and blood donation. Try to avoid iron supplements or iron fortified foods.
Copper also regulates iron and is antimicrobial, so consider eating copper rich foods (eg oysters, org beef liver), colloidal copper, although copper supplements are not necessarily good. Good old org chicken soup also great for viruses.