Mushrooms have evolved a variety of antimicrobial properties against bacteria and viruses that colonize them, some of which also infect humans. The MACH-19 investigators said they believe the combination of turkey tail and agarikon has the potential to impede COVID-19 by inhibiting viral replication, and they expect to test its antiviral effects in a phase 2 trial.
Source: https://jamanetwork.com/journals/jama/fullarticle/2786023