TABLE 1.

Studies regarding quercetin

Author	Year	Duration	Botanical compound	Species	Parameters	Results
Chen et al.	2011	48 hr	Houttuynia cordata Thunb., a plant containing flavonoids like quercetin, quercitrin, and isoquercitrin	Vero cells	The effect on HSV‐2 infection was determined by measuring cell viability using MTT assay	Quercetin, quercitrin, or isoquercitrin at 10 μM showed significant activity against HSV‐2 infection through inhibition of NF‐κB activation, while naringenin, a dihydroflavonoid from grape fruit showed no effect against HSV‐2 infection, indicating that the flavonoids are responsible for anti‐HSV‐2 activity in hot water extract of Houttuynia cordata
Cheng et al.	2019		Quercetin at various concentrations (2.5–20 μM)	ARPE‐19 cells	Quercetin effects on interleukin‐1β (IL‐1β)‐induced production of inflammatory cytokines and chemokines in ARPE‐19 cells	Quercetin could dose‐dependently decrease the mRNA and protein levels of ICAM‐1, IL‐6, IL‐8, and monocyte chemoattractant protein‐1 (MCP‐1). It also attenuated the adherence of the human monocytic leukaemia cell line THP‐1 to IL‐1β‐stimulated ARPE‐19 cells
Fanunza et al.	2020		A small set of flavonoids including quercetin and wogonin			Quercetin and wogonin can suppress the VP24 effect on IFN‐I signalling inhibition. Quercetin showed a half‐maximal inhibitory concentration (IC50) of 7.4 μM, and it was characterised to significantly restore the IFN‐I signalling cascade, blocked by VP24, by directly interfering with the VP24 binding to karyopherin‐α and thus restoring P‐STAT1 nuclear transport and IFN gene transcription. Quercetin significantly blocked viral infection, specifically targeting EBOV VP24 anti‐IFN‐I function
Heinz et al.	2010	12 weeks	Two quercetin doses (500 and 1,000 mg/day)	1,002 subjects	Upper respiratory tract infection rates	For all subjects combined, quercetin supplementation over 12 weeks had no significant influence on upper respiratory tract infection rates or symptomatology compared to placebo. A reduction in upper respiratory tract infection total sick days and severity was noted in middle aged and older subjects ingesting 1,000 mg quercetin/day for 12 weeks who rated themselves as physically fit
Luo et al.	2020	8.96 days	Herbs with a high quercetin content	54 patients with novel coronavirus pneumonia	Hemogram, days of hospitalisation	The clinical results of our study showed that 54 patients with novel coronavirus pneumonia enhanced immune ability against COVID‐19 by detecting blood samples after traditional Chinese medicine treatment and category of invigorating spleen and removing dampness appears to shorten patients' hospitalisation day