Indian Journal of Ophthalmology

: 2020  |  Volume : 68  |  Issue : 5  |  Page : 693--702

Therapeutic opportunities to manage COVID-19/SARS-CoV-2 infection: Present and future

Rohit Shetty1, Arkasubhra Ghosh2, Santosh G Honavar3, Pooja Khamar1, Swaminathan Sethu2,  
1 Narayana Nethralaya, Bangalore, Karnataka, India
2 GROW Research Laboratory, Narayana Nethralaya Foundation, Bangalore, Karnataka, India
3 Centre for Sight, Hyderabad, Telangana, India

Correspondence Address:
Dr. Swaminathan Sethu
GROW Research Laboratory, Narayana Nethralaya Foundation, Narayana Nethralaya, #258/A Hosur Road, Narayana Health City, Bommasandra, Bengaluru - 560 099, Karnataka


A severe form of respiratory disease – COVID-19, caused by SARS-CoV-2 infection, has evolved into a pandemic resulting in significant morbidity and mortality. The unabated spread of the disease is due to lack of vaccine and effective therapeutic agents against this novel virus. Hence, the situation demands an immediate need to explore all the plausible therapeutic and prophylactic strategies that can be made available to stem the spread of the disease. Towards this effort, the current review outlines the key aspects of the pathobiology associated with the morbidity and mortality in COVID-19 patients, which includes a viral response phase and an exaggerated host response phase. The review also summarizes therapeutic agents that are currently being explored along with those with potential for consideration. The broad groups of therapeutic agents discussed include those that: (i) block viral entry to host cells, (ii) block viral replication and survival in host cells, and (iii) dampen exaggerated host immune response. The various kinds of pharmaceutical prophylactic options that may be followed to prevent COVID-19 have also been discussed.

How to cite this article:
Shetty R, Ghosh A, Honavar SG, Khamar P, Sethu S. Therapeutic opportunities to manage COVID-19/SARS-CoV-2 infection: Present and future.Indian J Ophthalmol 2020;68:693-702

How to cite this URL:
Shetty R, Ghosh A, Honavar SG, Khamar P, Sethu S. Therapeutic opportunities to manage COVID-19/SARS-CoV-2 infection: Present and future. Indian J Ophthalmol [serial online] 2020 [cited 2023 May 29 ];68:693-702
Available from:

Full Text

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection associated respiratory disease – COVID-19 (2019-nCoV) evolved into a pandemic in about three months, from a cluster of pneumonia cases in China in mid-December 2019 to 267,013 cases in 184 countries with a mortality rate of 4.2% (11,201) as on March 22nd 2020.[1] The situation clearly indicates the urgent and immediate need to explore all the therapeutic and prophylactic strategies that can be made available to stem the spread of the disease.[2] Briefly, SARS-CoV-2 (family Coronaviridae; genus Betacoronavirus; subgenus Sarbecovirus) is an enveloped virus with a positive sense single-stranded RNA genome. It is suspected to have been transmitted from bats or through unknown intermediates to humans.[3] Effective human-to-human transmission even by asymptomatic and/or pre-symptomatic carriers has been a major reason underlying the rapid worldwide spread of the disease.[4],[5] It is known to be transmissible via direct contact, respiratory secretions and droplets, and could remain stable on surfaces for days.[6],[7] The presence of the virus in faecal swab, blood and tears or conjunctival secretions indicates that other modes of transmission are also plausible.[8],[9] High morbidity have been observed among the elderly, those with additional co-morbidities and those under immunosuppression.[10] Though the incubation period was reported to between 1 to 14 days, it has been found to be contagious even during the latency period.[11]

Current confirmatory diagnosis for SARS-CoV-2 infection is by the detection of its genome by real-time PCR in samples collected from nasal, throat swabs and/or blood.[3],[12] The results are sometimes validated by next-generation sequencing. Very recently, serological assays to determine the presence of virus by measuring antibody titres and seroconversion of SARS-CoV-2 have been developed and proposed for use.[13] The potential of such tests would be manifold, from prognosticating, identifying suitable convalescent serum and redeployment of health care personnel based on sero status. Another important aspect in risk stratification can also be based on HLA (Human Leukocyte Antigen) types, as earlier reports have shown association between specific HLA types and susceptibility or protection to SARS-CoV and MERS-CoV disease.[14],[15],[16],[17] Laboratory findings in COVID-19 shows lymphocytopenia, but high numbers of neutrophils, increased blood urea, creatinine and inflammatory factors were also observed.[18],[19],[20],[21]

Mechanisms underlying COVID-19 associated morbidity and mortality

SARS-CoV-2 causes COVID-19, which manifests as flu-like illness with fever, cough, sore throat, fatigue, dyspnoea, occasional diarrhoea and vomiting. In a select group of patients such as the elderlies and immunocompromised individuals, the condition deteriorates to acute respiratory distress syndrome (ARDS), septic shock and multi-organ failure resulting in mortality. As shown in [Figure 1], earlier and milder symptoms are due to viral infection and proportionate immune response to it (viral response phase). This phase can be managed by pharmaceutical agents directed against the various aspects of the viral life cycle. Most often, the grave morbidity and mortality associated with SAR-CoV-2 infection is due to the collateral damage caused by exaggerated and unabated immune response mounted by the host to protect against the infection (exaggerated host response phase).[22] This stage would require profound immune dampening along with anti-viral strategies.{Figure 1}

The milder symptoms that present during the viral response phase is due to the action of virus invading the respiratory mucosa and infecting the cells, which is sensed by the immune system that mounts a proportionate response against it. The envelope spike glycoprotein (S protein) of SARS-CoV-2 binds to its host cellular receptor Angiotensin-converting enzyme 2 (ACE2) on the cell surface to gain entry via both clathrin-dependent and -independent endocytosis.[23] The S protein then needs to be cleaved by cellular protease (serine protease, TMPRSS2), termed S protein priming, such that the viral and host cell membranes can fuse. After the nucleoprotein genome is released into the cytoplasm, the viral RNA directs a program of viral protein production and genome synthesis that results in subsequent viral replication and final release of virus from the cell.[24],[25] However, the presence of viral RNA genome triggers an anti-viral response through the activation of pattern recognition receptors such as toll-like receptors (TLR) -3, -7, -8 and 9. This protective response includes the induction of type 1 interferons and pro-inflammatory cytokines directed to stop viral propagation in the host cells.[25] Furthermore, presentation of the viral antigen by the infected cells also renders cellular and humoral immunity, in the form of virus-specific T cells and virus-specific antibody.[25] Pharmaceutical strategies that includes the blockade of viral entry to host cells and, blockade of viral replication and release would be effective in this phase to alleviate symptoms, reduce transmission and deterioration of the condition.

ARDS has been reported as the major cause of death among COVID-19 patients [18] and was the case with SARS-CoV and MERS-CoV infections.[26] Cytokine release syndrome (CRS), is characterized by large scale production and release of pro-inflammatory cytokines and chemokines due to hyper activation of the immune system causing damage to tissues and multi-organ failure.[27] This stage comprises of widespread injury to the vascular endothelium by the circulating inflammatory cytokines such as IL-6, IL-1 etc., followed by enhanced expression and presence of these inflammatory factors in the interstitial space resulting in injury to the tissue parenchyma. More recently, a report illustrated the absence of wound-healing macrophages, faster neutralizing antibody responses along with increased pro-inflammatory factors in patients who succumbed to SARS-CoV.[28] The immediate effort during ARDS is normally focussed on dampening the exaggerated immune response to prevent further damage to the tissues. A more effective approach is to prevent the progression of the disease by close monitoring and evidence based use of prophylactic immune modulation along with anti-viral agents.

Immunophenotyping efforts have indicated systemic and tissue specific immune profile in COVID-19 patients.[29],[30],[31],[32],[33] Along with the levels of inflammatory factors, the proportion of immune cells, its subsets, its activation status, its response and kinetics have been associated with disease state and prognosis.[29],[30],[31],[32],[33] Such information could be used to prognosticate or modulate specific immune cell subtypes to improve anti-viral immunity. However, as more data is reported on the disease progression and outcomes of therapy, a more consolidated profile will emerge with reference the status of immune cell and their role in COVID-19 pathobiology and disease resolution.

Strategies to mitigate COVID-19 associated morbidity and mortality

This section enumerates the various therapeutic agents along with their mechanism of action to target various aspects of the viral life cycle and exaggerated host immune response. The current and possible therapeutic strategies for the management of COVID-19/SARS-CoV-2 infection are summarized in [Figure 2] and [Table 1].{Figure 2}{Table 1}

Prevention of virus entry into host cells

Prevention of attachment

Since SARS-CoV-2 utilises the host cell surface receptor ACE2 to attach itself via its Spike protein (S) and gain entry,[34] it is an attractive target for preventing viral uptake. The options to block viral entry include the use of natural neutralizing antibodies from convalescent sera (discussed elsewhere in the manuscript) and engineered antibodies. Engineered antibodies or neutralizing fragments can be in various formats, such as soluble receptor-binding domain (based on SAR-S protein) that would occupy ACE2 and prevent access to SARS-CoV-2; antibodies or single chain variable fragment that would bind to ACE2 and prevent access to SARS-CoV-2, and soluble version of ACE2, which will bind to SAR-CoV-2, thus competitively sequestering it away from cell surface bound ACE2 in host cells.[35] The presence of Fc portion in natural and engineered antibodies or fragments would enable the elimination of the virus via phagocytosis and immune activation. It should be noted that due to the functional complexity that underlies renin angiotensin aldosterone system and the lack of robust information on the status of ACE2 expression in various tissue following the use of ACE inhibitors and angiotensin receptor blockers, it is difficult to speculate on the relevance of these ACE modulators in COVID-19.[36],[37] However, ACE inhibitors and angiotensin receptor blockers have been shown to decrease severe lung injury in certain virus mediated respiratory conditions.[36] Emodin (a naturally occurring anthraquinone) and promazine (phenothiazine class of anti-psychotics) have been shown to interrupt the binding of S protein with ACE2.[38] Further, drug-repurposing strategies have suggested possible small molecule drugs that may bind to S-protein to disrupt S protein-ACE2 interaction.[39],[40]

Prevention of fusion

The next critical stage in viral entry into the host cell is S protein priming, where the S protein needs to be cleaved by cellular proteases such as transmembrane protease serine 2 (TMPRSS2), furin and cathepsins for the viral and cellular membranes to fuse. Specifically, S protein priming by the serine protease TMPRSS2 is crucial for SARS-CoV infection of host target cells.[34],[41] Hence, targeting CoV entry by using protease inhibitors would be beneficial.[42],[43] TMPRSS2 is shown to be blocked by serine protease inhibitors such as camostat [34],[43] and nafamostat.[44]

Chloroquine, a 9-aminoquinoline is well-known for its effective use in the management and prevention of malaria. It evolved as an anti-viral agent by having more than one mechanism in inhibiting the viral life cycle. Firstly, as it is a weak base, it increases the pH of acidic vesicles such as endosomes and lysosomes, thereby preventing the viral envelope from uncoating and releasing the RNA into the host cell cytoplasm.[45],[46],[47] It is also known that chloroquine impairs virus replication, assembly and release.[45],[47] Chloroquine was also reported to impair glycosylation of ACE2 which could possibly interrupt the interaction between S protein and ACE2.[48],[49] Interestingly, anti-viral effects of chloroquine were observed in both pre- and post-infection conditions, opening up the possibility of its use as both prophylactic and therapeutic agent.[48] It has been proven to be effective against SARS-CoV-2 infection in vitro, particularly, hydroxychloroquine was observed to be more effective than chloroquine.[50],[51],[52] More importantly, the chloroquine (chloroquine phosphate or hydroxychloroquine) was also observed to beneficial in the management of COVID-19 patients by reducing deterioration of disease and virus load.[53],[54] It is considered that chloroquine's anti-viral and anti-inflammatory activities could have contributed to the therapeutic effects observed in COVID-19 patients.[53],[55] Since, identification of the SARS-CoV-2 virus in tears or conjunctival secretions [9] opened the possibility of additional modes of transmission, the use of chloroquine on the ocular surface [56],[57] can also be explored by studying the anti-viral effect using tolerable dose that can be used in eye drops.

Prevention of viral replication and survival in host cells

Viral protease inhibitor

Blocking key proteases such as coronavirus main protease (3CLpro) and papain-like protease (PLpro) are considered to be critical in blocking viral life cycle because they are necessary for the proteolysis of viral polyprotein into functional units.[58] Hence, Lopinavir-Ritonavir protease inhibitors were explored in the management of COVID-19. Unfortunately, no therapeutic benefit was observed with Lopinavir–Ritonavir treatment beyond the standard care.[59] However, this could be related to various factors such as the stage of the disease when it was administered, co-medications and adverse events that led to discontinuation of the regimen.[59] Cinanserin, flavonoids and diarylheptanoids have been reported to be inhibit 3CLpro or PLpro, hence, can be considered to be used to block SARS-CoV-2 replication.[60],[61] Another protease inhibitor, Nelfinavir, shown to inhibit SARS-CoV replication,[62] also has the potential to block SAR-CoV-2 replication.

Viral nucleic acid and protein synthesis inhibitors

Remdesivir, a nucleoside analog that blocks the RNA-dependent RNA polymerase, is showing great promise in the management of COVID-19 patient.[63] Interestingly, preclinical report suggests that the anti-viral activity of Remdesivir and type 1 interferon (IFNβ) was observed to be greater than

Lopinavir–Ritonavir–IFNβ against MERS-CoV.[64] Hence, a randomized, controlled clinical trial to evaluate the safety and efficacy of Remdesivir in COVID-19 has been initiated [65] and outcome of similar trials in China is awaited. Ribavirin, which is also a nucleoside analog, is used to inhibit viral RNA synthesis and viral mRNA capping. Interestingly, ribavirin and IFNβ synergistically inhibited the replication of SARS-associated coronavirus in animal and human cell lines.[66] Sofosbuvir, a nucleotide analog inhibitor, have been reported to exhibit potent anti-viral effects when used with ribavirin. More importantly, a report based on molecular docking showed tight binding of sofosbuvir and ribavirin to SARS-CoV-2 RNA-dependent RNA polymerase, thus suggesting its relevance in the management of COVID-19 patients.[67] Type 1 interferons such IFNα and IFNβ are endogenous anti-viral proteins produced by the host cells in response to viral infection, which degrade viral RNA and block viral protein synthesis and assembly.[68] Type 1 interferons have been available for clinical use for decades for the management of viral infection, tumours and auto-immune diseases.[69] The use of neuraminidase inhibitors such as oseltamivir and zanamivir have shown prevention of viral replication, budding and infectivity.[70],[71]

Combination treatments

Despite the favourable response observed with the use of Lopinavir-Ritonavir in the treatment of SARS,[72] the more recent effort against SARS-CoV-2 did not turn out to be effective.[59] Currently, Lopinavir-Ritonavir is being explored in combination with ribavirin and interferon-alpha [73] or interferon beta for MERS-CoV.[74] More recently, decrease in the viral load in COVID-19 patients by the use of hydroxychloroquine was observed to be enhanced in all the cases in the study arm when combined with azithromycin.[54] This beneficial effect was observed to be particularly higher in cases with concomitant upper or lower respiratory tract infections compared to asymptomatic patients.[54] Azithromycin was administered as a measure to prevent bacterial super-infection, it has been shown to have anti-viral effects as well.[75],[76] However, mechanism underlying the synergistic effect of hydroxychloroquine and azithromycin in decreasing the viral load is yet to be determined. Another combination of chloroquine with remdesivir was reported to be effective against SARS-CoV-2, albeit in vitro.[50] These studies open up the rational use of potentially effective combinatorial treatment in future for the management of COVID-19.

Active immunity

It is evident that vaccination is the ideal strategy to provide long lasting immunity to a large proportion of the at risk population. Unfortunately, there isn't any SAR-CoV-2 vaccine available at the moment. However, it is very encouraging that a total of 41 candidate vaccines are being developed against SAR-CoV-2 according to WHO's draft landscape of COVID-19 candidate vaccines as of 13 March 2020.[77] Different types of strategies such as DNA vaccine, RNA vaccine, live attenuated, formaldehyde inactivated, adenovirus-vector based, oral vaccine based, protein based and peptide based, are being employed against different components of SAR-CoV-2. Currently, one of the candidates is in Phase 1 clinical trial,[78] while the others are in various stages of preclinical development. The one in clinical trial, RNA-1273 is based on a RNA vaccine platform technology and is delivered via a novel lipid nanoparticle (LNP)-encapsulated mRNA against the stabilized spike protein.[78]

Passive immunity

The principle underlying this strategy is to neutralize the virus from infecting the host cells using antibodies (also called as neutralizing antibodies, NAb) against them that can be administered safely to individuals in need.[79],[80],[81],[82] NAbs can be obtained from the sera of patients from who have recovered from disease (convalescent sera) or can be engineered. Infected patients that recover completely, develop immunity against the virus that is likely mediated by either specific anti-viral antibodies or cell mediated immunity or both. This aspect has been harnessed by the use of convalescent sera/plasma therapy in the prevention and treatment of a variety of infections over decades, right from a century old Spanish flu to the more recent SARS and Ebola virus disease.[79],[80] World Health Organization (WHO) guidelines for the use of convalescent plasma in the management of Ebola virus disease [83] can be adapted for immediate need in case of COVID-19. This provides instant immunity to susceptible or high-risk individuals and is typically more effective when used prophylactically or soon after the onset of early symptoms. The effectiveness of this strategy can be achieved by following identification of sera containing high-titer of NAbs and also by mitigating the risk associated with transfer of blood substances (such as other infections, serum sickness) or possible antibody-dependent enhancement of infection.[84] Another aspect in providing passive immunity is by administering engineered neutralizing antibodies.[81] This is being evaluated to combat MERS-CoV in phase 1 trials.[82],[85] Very recently, an engineered human monoclonal antibody with the potential to block SARS-CoV-2 from infecting the cells has been developed.[86] Though it was shown that the mAb binds to the spike receptor binding region, it did not compete with ACE2 binding and is thought to neutralize the virus in a receptor independent fashion.[86] This approach emphasizes on engineering antibodies specific to the virus to prevent infection, reduce viral load or to be used in diagnostic systems.

Dampening hyper-immune activation and harnessing immune response

Corticosteroids, intravenous immunoglobulin (IVIg), monoclonal antibody based blockade of IL-6 (tocilizumab), interleukin 1 receptor antagonist protein (Anakinra) and JAK inhibition are the few strategies that have been proven to be effective in dampening exaggerated immune activation in a variety of diseases and treatment schedules.[27],[87],[88],[89] Hence, these will continue to be in the mainstream use in the management of cytokine release syndrome and associated pathologies in COVID-19 patients. In addition, to exaggerated response in later stages of the disease, dysregulated immune response was also observed in COVID-19 patients such as functionally exhausted cytotoxic T lymphocytes and natural killer cells due to increased expression of an inhibitory receptor, NKG2A that resulted in reduced anti-viral response.[32] These receptors can be blocked using monoclonal antibodies to yield therapeutic benefits.[90],[91] Hence, such selective modulation of activatory and inhibitory receptors on anti-viral responsive lymphocytes at different stages would enable us to harness the immune response to drive infection control and disease resolution.

Potential role of natural products from Indian traditional medicine

Due to the rapid spread of the disease, it is of general interest to also consider alternative remedies. There have been descriptions of anti-viral treatments, even targeted to the coronavirus family in Chinese Traditional Medicine.[92] Other natural products of Indian origin and Ayurvedic formulations have also been studied and used for their potential utility in various kinds of viral infections.[93] However, it should be noted that none of such natural products are actually tested to treat COVID-19. Typically, the presence of a variety of phytochemicals such as flavonoids, tannins, triterpenes, phenolic acids, alkaloids, saponins, lignins, proteins and peptides provide a plethora of functions to such natural products and extracts which have been demonstrated to modulate various aspects of viral infection including virus entry, viral gene expression and replication.[94] Although there is no direct evidence of the effect of such extracts, etc., on the SARS-CoV-2, common natural products such as curcumin and terpenoids can inhibit the CoV family member SARS [95] while Withania somnifera (Ashwagandha) have been demonstrated to inhibit other RNA virus.[96] Indeed several terpenoids and cannabinoids are being studied for their chemical action through docking studies on the viral protease are considered as possible prophylactic or therapeutic agents against SARS-CoV-2.[97] Various natural products and their combinations as enumerated in the Indian traditional health systems have been shown to have potent immunomodulatory and immune boosting effects [98] that may be helpful during the infection course. ARDS is a key pathological feature of COVID-19. Terpenoids (such as from neem plant, Azadirachta indica)[99] and curcumin [100] are effective in regulating the ARDS in animal models through the inhibition of the NFκB and associated pathways. Therefore, combinations of such natural products may have the potential to be used for prophylaxis and adjunct therapy to treat infected individuals.

Perspective on possible prophylactic measures

Since the spread of COVID-19, a large number of healthcare workers and doctors are directly exposed to the virus and hence susceptible to infection. To prevent spread of the virus in the general population as well, the currently available prophylactic measures are limited to reduction of contact with infected individuals, sanitisation and quarantine measures. However, there is a case to be made for drug prophylaxis. Such prophylactic treatments and vaccinations are commonplace during travel to areas where certain diseases are endemic. For example, chloroquine treatment is started prophylactically a week (500 mcg/week) before travel to areas where malaria is common. Nafamostat [101] and camostat [102] are used prophylactically to prevent pancreatitis. Anti-retroviral therapies are used prophylactically [103] to treat individuals at risk of contracting HIV. Therefore, we discuss here the various kinds of prophylactic options that may be followed in case of COVID-19.

The first group of prophylactic agents may consist of drugs that can inhibit the viral entry and genome release processes required for a successful infection. These include viral uptake receptor antibodies (ACE2 blocking antibodies, ARBs), competitive blockers of viral uptake (such as soluble ACE2), inhibitors of endocytosis and viral genome release (such as chloroquine – [Table 1]) and replication (such as Ribavirin) etc., It is interesting to note that Curcumin has been shownin vitro to inhibit the enveloped RNA viruses such as Zika and Chikungunya viruses [104] which may also be applicable to its mode of action against the SARS coronavirus family.[95] The second group of prophylactic agents may constitute of factors that enhances the anti-viral host immune response such as Imiquimod (imidazoquinolinamines) that enhance the secretion of type 1 interferon response.[105],[106],[107],[108] The potential prophylactic strategies to prevent SARS-CoV-2 infection is summarized in [Figure 3] and [Table 1].{Figure 3}

In conclusion, we illustrate the variety of potential therapeutic options currently available to us in the face of this incredible threat to human life. Most of the therapeutic options outlined have not undergone intensive pre-clinical and clinical testing, since, SARS-CoV-2 has not allowed scientists and clinicians that luxury. Yet, each of these various discussed modalities have merit in part due to their known activities, and in part due to the known mechanism of the viral infection course. Hence, all these modalities should be carefully considered in the right context at the time and duration of application.

Financial support and sponsorship

This work was supported by Narayana Nethralaya Foundation, Bangalore, India.

Conflicts of interest

There are no conflicts of interest.


1WHO, Coronavirus disease (COVID-2019) situation report 61. 2020.
2Baden LR, Rubin EJ. COVID-19-The search for effective therapy. N Engl J Med 2020. doi: 10.1056/NEJMe2005477
3Guo YR, Cao QD, Hong ZS, Tan YY, Chen SD, Jin HJ, et al. The origin, transmission and clinical therapies on coronavirus disease 2019 (COVID-19) outbreak – An update on the status. Mil Med Res 2020;7:11.
4Mizumoto K, Kagaya K, Zarebski A, Chowell G. Estimating the asymptomatic proportion of coronavirus disease 2019 (COVID-19) cases on board the Diamond Princess cruise ship, Yokohama, Japan, 2020. Eurosurveillance 2020;25. doi: 10.2807/1560-7917.ES.2020.25.10.2000180.
5Ganyani T, Kremer C, Chen D, Torneri A, Faes C, Wallinga J, et al. Estimating the generation interval for COVID-19 based on symptom onset data. 2020. Available from: DOI: 10.1101/2020.03.05.20031815 [Last accessed on 2020 Mar 21].
6Li Q, Guan X, Wu P, Wang X, Zhou L, Tong Y, et al. Early transmission dynamics in Wuhan, China, of novel coronavirus-infected pneumonia. N Engl J Med 2020. doi: 10.1056/NEJMoa2001316.
7van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, et al. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N Engl J Med 2020. doi: 10.1056/NEJMc2004973.
8Zhang W, Du RH, Li B, Zheng XS, Yang XL, Hu B, et al. Molecular and serological investigation of 2019-nCoV infected patients: Implication of multiple shedding routes. Emerg Microbes Infect 2020;9:386-9.
9Xia J, Tong J, Liu M, Shen Y, Guo D. Evaluation of coronavirus in tears and conjunctival secretions of patients with SARS-CoV-2 infection. J Med Virol 2020. doi: 10.1002/jmv. 25725.
10Yang X, Yu Y, Xu J, Shu H, Xia J, Liu H, et al. Clinical course and outcomes of critically ill patients with SARS-CoV-2 pneumonia in Wuhan, China: A single-centered, retrospective, observational study. Lancet Respir Med 2020. doi: 10.1016/S2213-2600(20) 30079-5.
11Jin YH, Cai L, Cheng ZS, Cheng H, Deng T, Fan YP, et al. A rapid advice guideline for the diagnosis and treatment of 2019 novel coronavirus (2019-nCoV) infected pneumonia (standard version). Mil Med Res 2020;7:4.
12Li X, Geng M, Peng Y, Meng L, Lu S. Molecular immune pathogenesis and diagnosis of COVID-19. J Pharm Anal 2020. doi: 10.1016/j.jpha. 2020.03.001.
13Amanat F, Nguyen T, Chromikova V, Strohmeier S, Stadlbauer D, Javier A, et al. A serological assay to detect SARS-CoV-2 seroconversion in humans. 2020. doi: 10.1101/2020.03.17.20037713.
14Keicho N, Itoyama S, Kashiwase K, Phi NC, Long HT, Ha LD, et al. Association of human leukocyte antigen class II alleles with severe acute respiratory syndrome in the Vietnamese population. Hum Immunol 2009;70:527-31.
15Chen YM, Liang SY, Shih YP, Chen CY, Lee YM, Chang L, et al. Epidemiological and genetic correlates of severe acute respiratory syndrome coronavirus infection in the hospital with the highest nosocomial infection rate in Taiwan in 2003. J Clin Microbiol 2006;44:359-65.
16Wang SF, Chen KH, Chen M, Li WY, Chen YJ, Tsao CH, et al. Human-leukocyte antigen class I Cw 1502 and class II DR 0301 genotypes are associated with resistance to severe acute respiratory syndrome (SARS) infection. Viral Immunol 2011;24:421-6.
17Hajeer AH, Balkhy H, Johani S, Yousef MZ, Arabi Y. Association of human leukocyte antigen class II alleles with severe Middle East respiratory syndrome-coronavirus infection. Ann Thorac Med 2016;11:211-3.
18Huang C, Wang Y, Li X, Ren L, Zhao J, Hu Y, et al. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet 2020;395:497-506.
19Yang W, Cao Q, Qin L, Wang X, Cheng Z, Pan A, et al. Clinical characteristics and imaging manifestations of the 2019 novel coronavirus disease (COVID-19):A multi-center study in Wenzhou city, Zhejiang, China. J Infect 2020;80:388-93.
20Guan WJ, Ni ZY, Hu Y, Liang WH, Ou CQ, He JX, et al. Clinical Characteristics of Coronavirus Disease 2019 in China. N Engl J Med 2020. doi: 10.1056/NEJMoa2002032.
21Liu K, Fang YY, Deng Y, Liu W, Wang MF, Ma JP, et al. Clinical characteristics of novel coronavirus cases in tertiary hospitals in Hubei Province. Chin Med J (Engl) 2020. doi: 10.1097/CM9.0000000000000744.
22Mehta P, McAuley DF, Brown M, Sanchez E, Tattersall RS, Manson JJ, et al. COVID-19: Consider cytokine storm syndromes and immunosuppression. Lancet 2020. doi: 10.1016/S0140-6736 (20) 30628-0.
23Wang H, Yang P, Liu K, Guo F, Zhang Y, Zhang G, et al. SARS coronavirus entry into host cells through a novel clathrin- and caveolae-independent endocytic pathway. Cell Res 2008;18:290-301.
24Perlman S, Netland J. Coronaviruses post-SARS: Update on replication and pathogenesis. Nat Rev Microbiol 2009;7:439-50.
25Perlman S, Dandekar AA. Immunopathogenesis of coronavirus infections: Implications for SARS. Nat Rev Immunol 2005;5:917-27.
26Park M, Thwaites RS, Openshaw PJM. COVID-19: Lessons from SARS and MERS. Eur J Immunol 2020;DOI: 10.1002/eji.202070035.
27Cron RQ, Behrens EM, editors. Cytokine Storm Syndrome. Switzerland AG, Springer Nature; 2019.
28Liu L, Wei Q, Lin Q, Fang J, Wang H, Kwok H, et al. Anti-spike IgG causes severe acute lung injury by skewing macrophage responses during acute SARS-CoV infection. JCI Insight 2019;4. doi: 10.1172/jci.insight. 123158.
29Thevarajan I, Nguyen THO, Koutsakos M, Druce J, Caly L, van de Sandt CE, et al. Breadth of concomitant immune responses prior to patient recovery: A case report of non-severe COVID-19. Nat Med 2020; DOI: 10.1038/s41591-020-0819-2.
30Zheng M, Gao Y, Wang G, Song G, Liu S, Sun D, et al. Functional exhaustion of antiviral lymphocytes in COVID-19 patients. Cell Mol Immunol 2020. doi: 10.1038/s41423-020-0402-2.
31Qin C, Zhou L, Hu Z, Zhang S, Yang S, Tao Y, et al. Dysregulation of immune response in patients with COVID-19 in Wuhan, China. Clin Infect Dis 2020. doi: 10.1093/cid/ciaa248.
32Liao M, Liu Y, Yuan J, Wen Y, Xu G, Zhao J, et al. The landscape of lung bronchoalveolar immune cells in COVID-19 revealed by single cell RNA sequencing. 2020: Available from: DOI: 10.1101/2020.02.23.20026690v1. [Last accessed on 2020 Mar 21].
33Cossarizza A, De Biasi S, Guaraldi G, Girardis M, Mussini C; Modena COVID-19 Working Group (MoCo19). SARS-CoV-2, the Virus that Causes COVID-19: Cytometry and the New Challenge for Global Health. Cytometry A 2020. doi: 10.1002/cyto.a. 24002.
34Hoffmann M, Kleine-Weber H, Schroeder S, Krüger N, Herrler T, Erichsen S, et al. SARS-CoV-2 cell entry depends on ACE2 and TMPRSS2 and is blocked by a clinically proven protease inhibitor. Cell 2020. doi: 10.1016/j.cell. 2020.02.052.
35Kruse RL. Therapeutic strategies in an outbreak scenario to treat the novel coronavirus originating in Wuhan, China. F1000Res 2020;9:72.
36Bozkurt B, Kovacs R, Harrington B. HFSA/ACC/AHA statement addresses concerns re: Using RAAS antagonists in COVID-19. 2020. Available from: [Last accessed on 2020 Mar 21].
37Fang L, Karakiulakis G, Roth M. Are patients with hypertension and diabetes mellitus at increased risk for COVID-19 infection? Lancet Respir Med 2020. doi: 10.1016/S2213-2600(20)30116-8.
38Ho TY, Wu SL, Chen JC, Li CC, Hsiang CY. Emodin blocks the SARS coronavirus spike protein and angiotensin-converting enzyme 2 interaction. Antiviral Res 2007;74:92-101.
39Smith M, Smith JC. Repurposing therapeutics for COVID-19: Supercomputer-based docking to the SARS-CoV-2 viral spike protein and viral spike protein-human ACE2 interface. Antiviral Res 2007;74:92-101.
40Liu C, Zhou Q, Li Y, Garner LV, Watkins SP, Carter LJ, et al. Research and development on therapeutic agents and vaccines for COVID-19 and related human coronavirus diseases. ACS Central Sci 2020. doi: 10.1021/acscentsci. 0c00272.
41Matsuyama S, Nao N, Shirato K, Kawase M, Saito S, Takayama I, et al. Enhanced isolation of SARS-CoV-2 by TMPRSS2-expressing cells. Proc Natl Acad Sci U S A, 2020. doi: 10.1073/pnas. 2002589117.
42Zhou Y, Vedantham P, Lu K, Agudelo J, Carrion R Jr, Nunneley JW, et al. Protease inhibitors targeting coronavirus and filovirus entry. Antiviral Res 2015;116:76-84.
43Shirato K, Kawase M, Matsuyama S. Middle East respiratory syndrome coronavirus infection mediated by the transmembrane serine protease TMPRSS2. J Virol 2013;87:12552-61.
44Yamamoto M, Matsuyama S, Li X, Takeda M, Kawaguchi Y, Inoue JI, et al. Identification of nafamostat as a potent inhibitor of Middle East respiratory syndrome coronavirus s protein-mediated membrane fusion using the split-protein-based cell-cell fusion assay. Antimicrob Agents Chemother 2016;60:6532-9.
45Savarino A, Boelaert JR, Cassone A, Majori G, Cauda R. Effects of chloroquine on viral infections: An old drug against today's diseases? Lancet Infect Dis 2003;3:722-7.
46Fauci A, Braunwald E, Kasper D, Hauser S, Longo D, Jameson JL,et al. Harrison's Principles of Internal Medicine. 17 ed. McGraw Hill Education; 2008.
47Al-Bari MAA. Targeting endosomal acidification by chloroquine analogs as a promising strategy for the treatment of emerging viral diseases. Pharmacol Res Perspect 2017;5:e00293.
48Vincent MJ, Bergeron E, Benjannet S, Erickson BR, Rollin PE, Ksiazek TG, et al. Chloroquine is a potent inhibitor of SARS coronavirus infection and spread. Virol J 2005;2:69.
49Savarino A, Di Trani L, Donatelli I, Cauda R, Cassone A. New insights into the antiviral effects of chloroquine. Lancet Infect Dis 2006;6:67-9.
50Wang M, Cao R, Zhang L, Yang X, Liu J, Xu M, et al. Remdesivir and chloroquine effectively inhibit the recently emerged novel coronavirus (2019-nCoV) in vitro. Cell Res 2020;30:269-71.
51Yao X, Ye F, Zhang M, Cui C, Huang B, Niu P, et al. In vitro antiviral activity and projection of optimized dosing design of hydroxychloroquine for the treatment of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Clin Infect Dis 2020. doi: 10.1093/cid/ciaa237.
52Liu J, Cao R, Xu M, Wang X, Zhang H, Hu H, et al. Hydroxychloroquine, a less toxic derivative of chloroquine, is effective in inhibiting SARS-CoV-2 infection in vitro. Cell Discov 2020;6:16. doi: 10.1038/s41421-020-0156-0.
53Gao J, Tian Z, Yang X. Chloroquine phosphate has shown apparent efficacy in treatment of COVID-19 associated pneumonia in clinical studies. BioSci Trends 2020;14:72-3.
54Gautret P, Lagier J, Parola P, Hoang VT, Meddeb L, Mailhe M, et al. Hydroxychloroquine and azithromycin as a treatment of COVID-19: Results of an open-label non-randomized clinical trial. Int J Antimicrobial Agents 2020; DOI: 10.1016/j.ijantimicag.2020.105949.
55Zhou D, Dai SM, Tong Q. COVID-19: A recommendation to examine the effect of hydroxychloroquine in preventing infection and progression. J Antimicrob Chemother 2020. doi: 10.1093/jac/dkaa114.
56Shivakumar S, Panigrahi T, Shetty R, Subramani M, Ghosh A, Jeyabalan N. Chloroquine protects human corneal epithelial cells from desiccation stress induced inflammation without altering the autophagy flux. Biomed Res Int 2018;2018:7627329.
57Bhavsar AS, Bhavsar SG, Jain SM. Evaluation of the effects of chloroquine phosphate eye drops in patients with dry eye syndrome. Int J Biomed Adv Res 2011;2(6).
58Chen Y, Liu Q, Guo D. Emerging coronaviruses: Genome structure, replication, and pathogenesis. J Med Virol 2020;92:418-23.
59Cao B, Wang Y, Wen D, Liu W, Wang J, Fan G. A trial of lopinavir–ritonavir in adults hospitalized with severe COVID-19. N Engl J Med 2020. doi: 10.1056/NEJMoa2001282.
60Jo S, Kim S, Shin DH, Kim MS. Inhibition of SARS-CoV 3CL protease by flavonoids. J Enzyme Inhib Med Chem 2020;35:145-51.
61Park JY, Jeong HJ, Kim JH, Kim YM, Park SJ, Kim D, et al. Diarylheptanoids from Alnus japonica inhibit papain-like protease of severe acute respiratory syndrome coronavirus. Biol Pharm Bull 2012;35:2036-42.
62Yamamoto N, Yang R, Yoshinaka Y, Amari S, Nakano T, Cinatl J, et al. HIV protease inhibitor nelfinavir inhibits replication of SARS-associated coronavirus. Biochem Biophys Res Commun 2004;318:719-25.
63Holshue ML, DeBolt C, Lindquist S, Lofy KH, Wiesman J, Bruce H, et al. First Case of 2019 Novel Coronavirus in the United States. N Engl J Med 2020;382:929-36.
64Sheahan TP, Sims AC, Leist SR, Schäfer A, Won J, Brown AJ, et al. Comparative therapeutic efficacy of remdesivir and combination lopinavir, ritonavir, and interferon beta against MERS-CoV. Nat Commun 2020;11:222.
65(NIAID), N.I.o.A.a.I.D., Adaptive COVID-19 Treatment Trial. 2020: Available from: [Last accessed on 2020 Mar 22].
66Morgenstern B, Michaelis M, Baer PC, Doerr HW, Cinatl J Jr. Ribavirin and interferon-beta synergistically inhibit SARS-associated coronavirus replication in animal and human cell lines. Biochem Biophys Res Commun 2005;326:905-8.
67Elfiky AA. Anti-HCV, nucleotide inhibitors, repurposing against COVID-19. Life Sci 2020;248:117477.
68Teijaro JR. Type I interferons in viral control and immune regulation. Curr Opin Virol 2016;16:31-40.
69Sathish JG, Sethu S, Bielsky MC, de Haan L, French NS, Govindappa K, et al. Challenges and approaches for the development of safer immunomodulatory biologics. Nat Rev Drug Discov 2013;12:306-24.
70McAuley JL, Gilbertson BP, Trifkovic S, Brown LE, McKimm-Breschkin JL. Influenza virus neuraminidase structure and functions. Front Microbiol 2019;10:39.
71Gong J, Xu W, Zhang J. Structure and functions of influenza virus neuraminidase. Curr Med Chem 2007;14:113-22.
72Chu CM, Cheng VC, Hung IF, Wong MM, Chan KH, Chan KS, et al. Role of lopinavir/ritonavir in the treatment of SARS: Initial virological and clinical findings. Thorax 2004;59:252-6.
73Kim UJ, Won EJ, Kee SJ, Jung SI, Jang HC. Combination therapy with lopinavir/ritonavir, ribavirin and interferon-alpha for Middle East respiratory syndrome. Antivir Ther 2016;21:455-9.
74Center, K.A.I.M.R., MERS-CoV Infection tReated With A Combination of lopinavir/ritonavir and interferon beta-1b (MIRACLE). 2019: Available from: [Last accessed on 2020 Mar 22].
75Bosseboeuf E, Aubry M, Nhan T, de Pina JJ, Rolain JM, Raoult D,et al. Azithromycin inhibits the replication of Zika virus. J Antivirals Antiretrovirals 2018;10:6-11.
76Madrid PB, Panchal RG, Warren TK, Shurtleff AC, Endsley AN, Green CE, et al. Evaluation of ebola virus inhibitors for drug repurposing. ACS Infect Dis 2015;1:317-26.
77WHO, DRAFT landscape of COVID-19 candidate vaccines – 20 March 2020. 2020: Available from: [Last accessed on 2020 Mar 21].
78(NIAID), N.I.o.A.a.I.D., Safety and Immunogenicity Study of 2019-nCoV Vaccine (mRNA-1273) to Prevent SARS-CoV-2 Infection. 2020: Available from: [Last accessed on 2020 Mar 22].
79Casadevall A, Pirofski LA. The convalescent sera option for containing COVID-19. J Clin Invest 2020. doi: 10.1172/JCI138003.
80Chen L, Xiong J, Bao L, Shi Y. Convalescent plasma as a potential therapy for COVID-19. Lancet Infect Dis 2020. Lancet Infect Dis 2020. doi: 10.1016/S1473-3099(20)30141-9.
81Lu RM, Hwang Y, Liu I, Lee Chi, Tsai H, Li H, et al. Development of therapeutic antibodies for the treatment of diseases. J Biomed Sci 2020;27:1.
82Beigel JH, Voell J, Kumar P, Raviprakash K, Wu H, Jiao JA, et al. Safety and tolerability of a novel, polyclonal human anti-MERS coronavirus antibody produced from transchromosomic cattle: A phase 1 randomised, double-blind, single-dose-escalation study. Lancet Infect Dis 2018;18:410-8.
83WHO, Use of convalescent whole blood or plasma collected from patients recovered from Ebola virus disease in WHO/HIS/SDS/2014.8, W.H. Organization, Editor. 2014.
84Wan Y, Shang J, Sun S, Tai W, Chen J, Geng Q, et al. Molecular mechanism for antibody-dependent enhancement of coronavirus entry. J Virol 2020;94. doi: 10.1128/JVI.02015-19.
85(NIAID), N.I.o.A.a.I.D., A Safety, Tolerability, Pharmacokinetics and Immunogenicity Trial of Co-administered MERS-CoV Antibodies REGN3048 and REGN3051. 2019: Available from: [Last accessed on 2020 Mar 22].
86Wang C, Li W, Drabek D, Okba NM, van Haperen R, Osterhaus ADME, et al. A human monoclonal antibody blocking SARS-CoV-2 infection. bioRxiv, 2020. doi: 10.1101/2020.03.11.987958. [Last accessed on 2020 Mar 21].
87Riegler LL, Jones GP, Lee DW. Current approaches in the grading and management of cytokine release syndrome after chimeric antigen receptor T-cell therapy. Ther Clin Risk Manag 2019;15:323-35.
88Gerlach H. Agents to reduce cytokine storm. F1000Res 2016;5:2909.
89Liu Q, Zhou YH, Yang ZQ. The cytokine storm of severe influenza and development of immunomodulatory therapy. Cell Mol Immunol 2016;13:3-10.
90André P, Denis C, Soulas C, Bourbon-Caillet C, Lopez J, Arnoux T, et al. Anti-NKG2A mAb Is a checkpoint inhibitor that promotes anti-tumor immunity by unleashing both T and NK cells. Cell 2018;175:1731-43.
91Creelan BC, Antonia SJ. The NKG2A immune checkpoint-A new direction in cancer immunotherapy. Nat Rev Clin Oncol 2019;16:277-8.
92Lin LT, Hsu WC, Lin CC. Antiviral natural products and herbal medicines. J Tradit Complement Med 2014;4:24-35.
93Dhama K, Karthik K, Khandia R, Munjal A, Tiwari R, Rana R, et al. Medicinal and therapeutic potential of herbs and plant metabolites/extracts countering viral pathogens-current knowledge and future prospects. Curr Drug Metab 2018;19:236-63.
94Ganjhu RK, Mudgal PP, Maity H, Dowarha D, Devadiga S, Nag S, et al. Herbal plants and plant preparations as remedial approach for viral diseases. Virusdisease 2015;26:225-36.
95Wen CC, Kuo YH, Jan JT, Liang PH, Wang SY, Liu HG, et al. Specific plant terpenoids and lignoids possess potent antiviral activities against severe acute respiratory syndrome coronavirus. J Med Chem 2007;50:4087-95.
96Ganguly B, Umapathi V, Rastogi SK. Nitric oxide induced by Indian ginseng root extract inhibits infectious bursal disease virus in chicken embryo fibroblasts in vitro. J Anim Sci Technol 2018;60:2.
97Shaghaghi N. Molecular Docking Study of Novel COVID-19 Protease with Low Risk Terpenoides Compounds of Plants. 2020: Available from: DOI: 10.26434/chemrxiv.11935722.v1. [Last accessed on 2020 Mar 21].
98Kumar D, Arya V, Kaur R, Bhat ZA, Gupta VK, Kumar V. A review of immunomodulators in the Indian traditional health care system. J Microbiol Immunol Infect 2012;45:165-84.
99Pooladanda V, Thatikonda S, Bale S, Pattnaik B, Sigalapalli DK, Bathini NB, et al. Nimbolide protects against endotoxin-induced acute respiratory distress syndrome by inhibiting TNF-alpha mediated NF-kappaB and HDAC-3 nuclear translocation. Cell Death Dis 2019;10:81.
100Avasarala S, Zhang F, Liu G, Wang R, London SD, London L. Curcumin modulates the inflammatory response and inhibits subsequent fibrosis in a mouse model of viral-induced acute respiratory distress syndrome. PLoS One 2013;8:e57285.
101Chang JH, Lee IS, Kim HK, Cho YK, Park JM, Kim SW, et al. Nafamostat for prophylaxis against post-endoscopic retrograde cholangiopancreatography pancreatitis compared with gabexate. Gut Liver 2009;3:205-10.
102Lankisch PG, Pohl U, Goke B, Otto J, Wereszczynska-Siemiatkowska U, Gröne H-J, et al. Effect of CAMOSTAT on acute pancreatitis. Biomed Res 1989;10(Suppl 1):51-6.
103Krakower DS, Jain S, Mayer KH. Antiretrovirals for primary HIV prevention: The current status of pre- and post-exposure prophylaxis. Curr HIV/AIDS Rep 2015;12:127-38.
104Mounce BC, Cesaro T, Carrau L, Vallet T, Vignuzzi M. Curcumin inhibits Zika and chikungunya virus infection by inhibiting cell binding. Antiviral Res 2017;142:148-57.
105Dockrell DH, Kinghorn GR. Imiquimod and resiquimod as novel immunomodulators. J Antimicrob Chemother 2001;48:751-5.
106Goldstein D, Hertzog P, Tomkinson E, Couldwell D, McCarville S, Parrish S, et al. Administration of imiquimod, an interferon inducer, in asymptomatic human immunodeficiency virus-infected persons to determine safety and biologic response modification. J Infect Dis 1998;178:858-61.
107Barbosa Ldo N, Souto R, Furtado AL, Gripp AC, Daxbacher E. Association of oral acyclovir and imiquimod for the treatment of hypertrophic genital herpes simplex in HIV positive patients: Report of two cases. An Bras Dermatol 2011;86:1043-5.
108Bryden SR, Pingen M, Lefteri DA, Miltenburg J, Delang L, Jacobs S, et al. Pan-viral protection against arboviruses by activating skin macrophages at the inoculation site. Sci Transl Med 2020;12. doi: 10.1126/scitranslmed.aax2421.