In addition to antiviral therapy, immunomodulatory drugs are also being used as treatment strategies to suppress hyperinflammation and to reduce death among COVID-19 patients (Mehta et al., 2020) . Corticosteroids have a long history of use in severe cases of coronavirus disease, including SARS, MERS, and COVID-19, as immunomodulatory drugs (Arabi et al., 2018; Huang et al., 2020; So et al., 2003) . Recently, dexamethasone (a synthetic adrenal corticosteroid), whose demand has surged suddenly after publication of the preprint paper of the RECOVERY trial (https://www.medrxiv.org/content/10.1101/2020. 06.22.20137273v1.full.pdf) , was found to be the first drug, which successfully reduced deaths in approximately one-third of critically ill F I G U R E 1 Schematic representation of possible antiinflammatory effects of quercetin against SARS-CoV-1/2. Quercetin has been demonstrated to inhibit SARS-CoV-1/2 entry inside cell by interfering with the expression of ACE2. Further, quercetin initiates IFN-γ production by T lymphocytes, which enhances anti-viral activity and antigen presentation by phagocytocytosis, and expression of MHC-I and MHC-II molecules. Decrement of inflammation and blood clotting in lungs is achieved by inhibition of IL-8 production by quercetin. Importantly, quercetin also inhibits the production of IL-4 and TNF-α, which helps in ameliorating inflammation. ACE2, Angiotensinconverting enzyme 2; IL, Interleukin; IFN-γ, Interferon-gamma; TNF-α, Tumor necrosis factor-alpha; SARS-CoV, Severe acute respiratory syndrome coronavirus [Colour figure can be viewed at wileyonlinelibrary.com] COVID-19 patients, who were on invasive mechanical ventilation support and by one-fifth in noninvasive ventilated patients. Interestingly, no positive outcome was reported from less severe COVID-19 patients, who were without any oxygen support. Likewise, in another randomized controlled trial (RCT), dexamethasone reduced mortality in ARDS patients (Villar et al., 2020) . The findings of Selvaraj, Dapaah-Afriyie, Finn, and Flanigan (2020) also support the use of dexamethasone in COVID-19 treatment, where the short-term course of dexamethasone prevented disease severity and in turn reduced the length of ICU stay of patients with hypoxic respiratory failure.
Dexamethasone, by suppressing the immune response, helps to overcome serious manifestations caused by the hyperactive immune response in COVID-19 patients. However, in the absence of adequate RCTs, there has always been controversy regarding the use of corticosteroids. The limiting element is the lack of standardization of various aspects, such as drug dose, route of administration, bioavailability, side effects and exact therapeutic impacts in patients. It has been observed that corticosteroid treatment prolonged the viral presence in SARS-CoV-1 patients (Lee et al., 2004) , and their administration in low doses had no impact on virus clearance in COVID-19 patients (Fang et al., 2020) . Because of several contradictory outcomes, it seems difficult to support the routine use of corticosteroids in COVID-19 disease management. Even existing guidelines of the World Health Organization (WHO) are not in favor of the routine use of corticoseroides in SARS-CoV-2 patients. In such a scenario, we searched for a suitable alternate option that can either augment or substitute dexamethasone action in dexamethasone-nonresponsive severely ill Covid-19 patients and for mild and moderate Covid-19 cases. At this point, it is imperative to discuss an interesting fact that Bhutto et al. (2018) identified molecular as well as functional similarity between dexamethasone and quercetin, [permeability-glycoprotein (P-gp) inducers]. P-gp, a membrane transporter, helps in the retention of various drugs, but pro-inflammatory cytokines released during infections have been observed to inhibit its expression and activity (Iqbal et al., 2012) . As P-gp inducers, both dexamethasone and quercetin, by interfering with p-gp expression, can inhibit the "cytokine Due to pleiotropic properties and capability to synergize with conventional drugs, it is assumed that flavonoids can reduce both transmembrane peptidase serine 2 (TMPRSS2) and Furin, which F I G U R E 2 Schematic representation of different stages of SARS-CoV-1 replication cycle inhibited by quercetin and zinc. Viral attachment (1), viral entry (2), preparation for viral uncoating (3), viral uncoating, and release of viral genome and viral protein (4), viral transcription (5), viral protein translation (6), viral replication (5), virus assembly and maturation (7) and, finally mature viral particles release (8). Quercetin has been demonstrated to inhibit SARS-CoV-1 entry (2) step, whereas, zinc inhibits SARS-CoV-1 genome transcription by inhibiting viral RdRp in a dose dependent manner(Step 5). ACE2, Angiotensin-converting enzyme 2; RdRp, RNA-dependent RNA polymerase; SARS-CoV, Severe acute respiratory syndrome coronavirus; Zn, zinc [Colour figure can be viewed at wileyonlinelibrary.com] cleave the SARS-CoV-2 Spike protein enabling SARS-CoV-2 infection (Russo, Moccia, Spagnuolo, Tedesco, & Russo, 2020) . Yi et al. (2004) specifically revealed that quercetin and another related flavonoid, luteolin, can inhibit the entry of SARS virus inside the host cell. Quercetin seems to impede the entry of SARS virus by targeting angiotensin-converting enzyme 2 (ACE2) expression (ACE2 gene expression is required for SARS-CoV-2 entry into human cells) ( Figure 1) (Glinsky, 2020) . Quercetin modulates the cellular unfolded protein response, which is utilized by viruses to complete its life cycle (Nabirotchkin, Peluffo, Bouaziz, & Cohen, 2020) . Study of Abian et al. (2020) is a direct evidence of quercetin's efficacy to target SARS-CoV-2 3C-like protease (3CLpro) on solid experimental bases.
In vitro studies have revealed the immunomodulatory effects of quercetin, which prevents the production of tumor necrosis factor-α in macrophages (Manjeet & Ghosh, 1999) and interleukin (IL)-8 production in lung cells (Geraets et al., 2007) . It is pertinent here to note that production of interferon-gamma (Th-1-derived cytokine) and the inhibition of IL-4 (Th-2-derived cytokine) may be responsible for the beneficial immunostimulatory effects of quercetin (Figure 1) (Nair et al., 2002) . Moreover, it is tempting to speculate that due to quercetin's zinc ionophore property, it along with zinc can be a potential 