Table 3: Summary of the evidence for the use of Flavonoids and Polyphenols in COVID-19.

References Type of Study Results/ Conclusions
Deep et al. [69] Bench/Lab study They reported in conclusion that flavonoids: Hesperidine, Naringin, and Epigallocatechin Gallate (EGCG), were potent inhibitors of the nCoV-SP receptor-binding domain of S protein (RBD). At the same time, Quercetin showed affinity to human receptor human angiotensin-converting enzyme-2 (ACE-2) and found to be more efficient towards the viral spike glycoprotein. Quercetin effectively blocked the human ACE-2 receptor by binding to a substantial residue ASP38 and hindered the formation of the salt bridge with LYS353 and, ultimately, the well-recognized hotspot LYS353, which is well recognized by SARS-CoV-2.
Adem et al. [70] Bench/ Lab Study After Molecular docking, the study found that flavonoids like hesperidin and rutin may bind the main protease (Mpro) of COVID-19 better than Nelfinavir.
Bhatia et al. [71] Bench/ Lab Study They performed Virtual Screening by Molecular Docking approach, which established the top 6 docked polyphenols, which are primarily derivatives of Sanguiin, Theaflavin, Kaempferol, Punicalagin, and Protocatechuic acid. Sanguiin and Theaflavin were proposed to resolve breathing difficulties in patients with extreme COVID-19, as they already are established bronchodilators.
Ang et al. [72] Systematic review The team reviewed 12 pattern identifications, herbal compositions, and analyzed their herbal formulae, recommended by Chinese guidelines for the treatment of various pediatric COVID-19 stages. After thorough analysis, the herb Armeniacae semen was found to be most frequently used for the treatment of pediatric COVID-19 in the Chinese population. It reduced hyper-responsiveness in the airways and inhibited Th2 cells.