Кверцитин in silico показал антивирусный эффект:
https://www.preprints.org/manuscript/202003.0226/v1/
Potential Inhibitor of COVID-19 Main Protease (Mpro)

The docking analysis in the present study showed the inhibition potential of several compounds, ranked by affinity:

nelfinavir > lopinavir > kaempferol > quercetin > luteolin-7-glucoside > demethoxycurcumin > naringenin > apigenine-7-glucoside > oleuropein > curcumin > catechin > epigallocatechin > zingerol > gingerol > allicin.

Возможно, кверцитин имеет противовоспалительный эффект:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4808895/

Но у кверцитина низкая bioavailability при оральном применении.