ABSTRACT
Understanding the differences in serum cross-neutralizing responses against SARS-CoV-2 variants, including Omicron sub-lineages BA.5, BA.2.75, and BQ.1.1, elicited by exposure to distinct antigens is essential for developing COVID-19 booster vaccines with enhanced cross-protection against antigenically distinct variants. However, fairly comparing the impact of breakthrough infection on serum neutralizing responses to several variants with distinct epidemic timing is challenging because responses after breakthrough infection are affected by the exposure interval between vaccination and infection. We assessed serum cross-neutralizing responses to SARS-CoV-2 variants, including Omicron sub-lineages, in individuals with breakthrough infections before or during the Omicron BA.1 epidemic. To understand the differences in serum cross-neutralizing responses after pre-Omicron or Omicron breakthrough infection, we used Bayesian hierarchical modeling to correct the cross-neutralizing responses for the exposure interval between vaccination and breakthrough infection. The exposure interval required to generate saturated cross-neutralizing potency against each variant differed by variant, with variants more antigenically distant from the ancestral strain requiring a longer interval. Additionally, Omicron breakthrough infection was estimated to have higher impact than booster vaccination and pre-Omicron breakthrough infection on inducing serum neutralizing responses to the ancestral strain and Omicron sub-lineages. However, the breadth of cross-neutralizing responses to Omicron sub-lineages, including BQ.1.1, after Omicron or pre-Omicron breakthrough infection with the ideal exposure interval were estimated to be comparable. Our results highlight the importance of optimizing the interval between vaccine doses for maximizing the breadth of cross-neutralizing activity elicited by booster vaccines with or without Omicron antigen.
Subject(s)
Breakthrough Pain , COVID-19ABSTRACT
The diversity of SARS-CoV-2 mutations raises the possibility of reinfection of individuals previously infected with earlier variants, and this risk is further increased by the emergence of the B.1.1.529 Omicron variant. In this study, we used an in vivo, hamster infection model to assess the potential for individuals previously infected with SARS-CoV-2 to be reinfected with Omicron variant and we also investigated the pathology associated with such infections. Initially, Syrian hamsters were inoculated with a lineage A, B.1.1.7, B.1.351, B.1.617.2 or a subvariant of Omicron, BA.1 strain and then reinfected with the BA.1 strain 5 weeks later. Subsequently, the impact of reinfection with Omicron subvariants (BA.1 and BA.2) in individuals previously infected with the BA.1 strain was examined. Although viral infection and replication were suppressed in both the upper and lower airways, following reinfection, virus-associated RNA was detected in the airways of most hamsters. Viral replication was more strongly suppressed in the lower respiratory tract than in the upper respiratory tract. Consistent amino acid substitutions were observed in the upper respiratory tract of infected hamsters after primary infection with variant BA.1, whereas diverse mutations appeared in hamsters reinfected with the same variant. Histopathology showed no acute pneumonia or disease enhancement in any of the reinfection groups and, in addition, the expression of inflammatory cytokines and chemokines in the airways of reinfected animals was only mildly elevated. These findings are important for understanding the risk of reinfection with new variants of SARS-CoV-2.
Subject(s)
Pneumonia , Virus DiseasesABSTRACT
The prevalence of the Omicron subvariant BA.2.75 is rapidly increasing in India and Nepal. In addition, BA.2.75 has been detected in at least 34 other countries and is spreading globally. However, the virological features of BA.2.75 are largely unknown. Here, we evaluated the replicative ability and pathogenicity of BA.2.75 clinical isolates in Syrian hamsters. Although we found no substantial differences in weight change among hamsters infected with BA.2, BA.5, or BA.2.75, the replicative ability of BA.2.75 in the lungs was higher than that of BA.2 and BA.5. Of note, BA.2.75 caused focal viral pneumonia in hamsters, characterized by patchy inflammation interspersed in alveolar regions, which was not observed in BA.5-infected hamsters. Moreover, in competition assays, BA.2.75 replicated better than BA.5 in the lungs of hamsters. These results suggest that BA.2.75 can cause more severe respiratory disease than BA.5 and BA.2 and should be closely monitored.
Subject(s)
Respiratory Tract Diseases , Adenocarcinoma, Bronchiolo-Alveolar , PneumoniaABSTRACT
The BA.2 sublineage of the SARS-CoV-2 Omicron variant has become dominant in most countries around the world; however, the prevalence of BA.4 and BA.5 is increasing rapidly in several regions. BA.2 is less pathogenic in animal models than previously circulating variants of concern (VOC). Compared with BA.2, however, BA.4 and BA.5 possess additional substitutions in the spike protein, which play a key role in viral infectivity, raising concerns that the infectivity and pathogenicity of BA.4 and BA.5 are higher than those of BA.2. Here, we evaluated the replicative ability and pathogenicity of authentic BA.4 and BA.5 isolates in wild-type Syrian hamsters and human ACE2 (hACE2) transgenic hamsters. In contrast to recent data with a recombinant chimeric virus possessing the spike protein of BA.4/BA.5 in the background of a BA.2 strain, we observed no obvious differences among BA.2, BA.4, and BA.5 isolates in growth ability or pathogenicity in hamsters, and less pathogenicity compared to a previously circulating Delta (B.1.617.2 lineage) isolate. In addition, in vivo competition experiments revealed that BA.5 outcompeted BA.2 in hamsters, whereas BA.4 and BA.2 exhibited similar fitness. These findings suggest that BA.4 and BA.5 have similar pathogenicity to BA.2 in rodents and that BA.5 possesses viral fitness superior to that of BA.2. Our study highlights the importance of using authentic isolates when evaluating virological features.
ABSTRACT
AbstractImmunity to SARS-CoV-2 in COVID-19 cases has diversified due to complex combinations of exposure to vaccination and infection. Elucidating the drivers for upgrading neutralizing activity to SARS-CoV-2 in COVID-19 cases with pre-existing immunity will aid in understanding immunity to SARS-CoV-2 and improving COVID-19 booster vaccines with enhanced cross-protection against antigenically distinct variants. This study revealed that the magnitude and breadth of neutralization responses to SARS-CoV-2 infection in breakthrough infections are determined by upper respiratory viral load and vaccination-infection time interval, but not by the lineage of infecting viruses. Notably, the time interval, but not the viral load, may play a critical role in expanding the breadth of neutralization to SARS-CoV-2. This illustrates the importance of dosing interval optimization in addition to antigen design in the development of variant-proof booster vaccines. One-Sentence SummaryViral load and infection timing define the magnitude and breadth of SARS-CoV-2 neutralization after breakthrough infection.
Subject(s)
COVID-19 , Breakthrough Pain , Encephalomyelitis, Acute DisseminatedABSTRACT
The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron subvariant BA.2 has spread in many countries, replacing the earlier Omicron subvariant BA.1 and other variants. Here, using a cell culture infection assay, we quantified the intrinsic sensitivity of BA.2 and BA.1 compared with other variants of concern, Alpha, Gamma, and Delta, to five approved-neutralizing antibodies and antiviral drugs. Our assay revealed the diverse sensitivities of these variants to antibodies, including the loss of response of both BA.1 and BA.2 to casirivimab and of BA.1 to imdevimab. In contrast, EIDD-1931 and nirmatrelvir showed a more conserved activities to these variants. The viral response profile combined with mathematical analysis estimated differences in antiviral effects among variants in the clinical concentrations. These analyses provide essential evidence that gives insight into the impact of variant emergence on choosing optimal drug treatment.
Subject(s)
Coronavirus InfectionsABSTRACT
Background: The Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was identified in Japan in November 2021. This variant contains up to 36 mutations in the spike protein, the target of neutralizing antibodies, and can escape vaccine-induced immunity. The third booster vaccination campaign began with healthcare workers and high-risk groups. The safety and immunogenicity of third booster vaccination against Omicrons remain unknown. Methods: In total, 272 healthcare workers were evaluated for their long-term safety and immunogenicity. Here, we established vaccine panels to evaluate the safety and immunogenicity against variants of concern (VOCs), including the Omicron variant, using a live virus microneutralization assay. Findings: Two-dose vaccination induced robust anti-spike antibodies and neutralization titers (NTs) against the ancestral strain WK-521, whereas NTs in VOCs were significantly decreased. Within 93-247 days of the second vaccine dose, NTs against Omicron were completely abolished in up to 80% of individuals among the vaccine panels. The third booster vaccination induced a robust increase in anti-spike antibodies and NTs against the WK-521, Delta, and Omicron variants. The breadth of humoral immunity and cross-reactivity with Omicron increased. The cytokine signature and adverse event rate remained unchanged after three dose vaccination. Conclusions: The third vaccination dose is safe and effective against Omicron infection.
Subject(s)
Coronavirus InfectionsABSTRACT
Background The immune profile against SARS-CoV-2 has dramatically diversified due to a complex combination of exposure to vaccines and infection by various lineages/variants, likely generating a heterogeneity in protective immunity in a given population. To further complicate this, the Omicron variant, with numerous spike mutations, has emerged. These circumstances have created the need to assess the potential of immune evasion by the Omicron in individuals with various immune histories. Methods The neutralization susceptibility of the variants including the Omicron and their ancestor was comparably assessed using a panel of plasma/serum derived from individuals with divergent immune histories. Blood samples were collected from either mRNA vaccinees or from those who suffered from breakthrough infections by the Alpha/Delta with multiple time intervals following vaccination. Findings The Omicron was highly resistant to neutralization in fully vaccinated individuals without a history of breakthrough infections. In contrast, robust cross-neutralization against the Omicron were induced in vaccinees that experienced breakthrough infections. The time interval between vaccination and infection, rather than the variant types of infection, was significantly correlated with the magnitude and potency of Omicron-neutralizing antibodies. Conclusions Immune histories with breakthrough infections can overcome the resistance to infection by the Omicron, with the vaccination-infection interval being the key determinant of the magnitude and breadth of neutralization. The diverse exposure history in each individual warrants a tailored and cautious approach to understanding population immunity against the Omicron and future variants. Funding This study was supported by grants from the Japan Agency for Medical Research and Development (AMED).
Subject(s)
Breakthrough Pain , Death , Encephalomyelitis, Acute DisseminatedABSTRACT
SARS-CoV-2 Beta and Omicron variants have multiple mutations in the receptor-binding domain (RBD) allowing antibody evasion. Despite the resistance to circulating antibodies in those who received two doses of mRNA vaccine, the third dose prominently recalls cross-neutralizing antibodies with expanded breadth to these variants. Herein, we longitudinally profiled the cellular composition of persistent memory B-cell subsets and their antibody reactivity against these variants following the second vaccine dose. The vaccination elicited a memory B-cell subset with resting phenotype that dominated the other subsets at 4.9 months. Notably, most of the resting memory subset retained the ability to bind the Beta variant, and the memory-derived antibodies cross-neutralized the Beta and Omicron variants at frequencies of 59% and 29%, respectively. The preservation of cross-neutralizing antibody repertoires in the durable memory B-cell subset likely contributes to the prominent recall of cross-neutralizing antibodies following the third dose of the vaccine. One Sentence Summary Fully vaccinated individuals preserve cross-neutralizing memory B-cells against the SARS-CoV-2 Omicron variant.
ABSTRACT
Potently neutralizing SARS-CoV-2 antibodies often target the receptor binding site (RBS) of spike protein but the variability of RBS epitopes hampers broad neutralization of different clades of coronaviruses and emerging drifted viruses. Here, we identified a human RBS antibody that potently neutralizes SARS-CoV and SARS-CoV-2 variants that belong to clade 1 SARS-related coronavirus. X-ray crystallography revealed coordinated recognition by the heavy chain to conserved sites and the light chain to RBS, allowing for the mimicry of ACE2 binding mode. The minimum footprints in the hypervariable region of RBS contributed to the breadth of neutralization, and the activity was further enhanced by IgG3 switching. Eventually, the coordinated binding resulted in broad neutralization of SARS-CoV and emerging SARS-CoV-2 variants of concern. Furthermore, therapeutic treatment in a hamster model provided protection at low dosage. The structural basis for broadly neutralizing activity informs the design of broad spectrum of therapeutics and vaccines.Funding: This work was supported by Japan Agency for Medical Research and Development grant JP19fk0108111 (TH, YT), JP20fk0108298 (TK, TH, KM, YT), JP20am0101093 (KM), JP20ae0101047 (KM), JP20fk0108251 (HS), and JP20am0101124 (YK), by Ministry of Education, Culture, Sports, Science and Technology grant JPMXS0420100119 (KM) and 20H05773 (TH), by The Naito Foundation (TH), and by Joint Usage/Research Center program of Institute for Frontier Life and Medical Sciences, Kyoto University (KM).Conflict of Interest: AS is an employee of Shionogi & Co., Ltd. MO is a CEO, employee, and shareholder of Trans Chromosomics, Inc. These authors acknowledge a potential conflict of interest and attest that the work contained in this report is free of any bias that might be associated with the commercial goals of the company. TO, YA, MO, TH, KM, and YT declare that an intellectual property application has been filed using the data presented in this paper. The other authors declare that they have no competing interests.Ethical Approval: Animal procedures were approved by the Animal Ethics Committee of the National Institute of Infectious Diseases, Japan, and performed in accordance with the guidelines of the Institutional Animal Care and Use Committee. In vitro escape mutation screening experiments for SARSCoV-2 were performed at the Biosafety Level-3 facility of the Research Center for ZoonosisControl, Hokkaido University, and the National Institute of Infectious Diseases following the institutional guidelines.
Subject(s)
Communicable DiseasesABSTRACT
Coronavirus disease 2019 (COVID-19) has caused serious public health, social, and economic damage worldwide and effective drugs that prevent or cure COVID-19 are urgently needed. Approved drugs including Hydroxychloroquine, Remdesivir or Interferon were reported to inhibit the infection or propagation of severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2), however, their clinical efficacies have not yet been well demonstrated. To identify drugs with higher antiviral potency, we screened approved anti-parasitic/anti-protozoal drugs and identified an anti-malarial drug, Mefloquine, which showed the highest anti-SARS-CoV-2 activity among the tested compounds. Mefloquine showed higher anti-SARS-CoV-2 activity than Hydroxychloroquine in VeroE6/TMPRSS2 and Calu-3 cells, with IC50 = 1.28 M, IC90 = 2.31 M, and IC99 = 4.39 M in VeroE6/TMPRSS2 cells. Mefloquine inhibited viral entry after viral attachment to the target cell. Combined treatment with Mefloquine and Nelfinavir, a replication inhibitor, showed synergistic antiviral activity. Our mathematical modeling based on the drug concentration in the lung predicted that Mefloquine administration at a standard treatment dosage could decline viral dynamics in patients, reduce cumulative viral load to 7% and shorten the time until virus elimination by 6.1 days. These data cumulatively underscore Mefloquine as an anti-SARS-CoV-2 entry inhibitor.
Subject(s)
COVID-19ABSTRACT
Background:SARS-CoV-2 is a novel coronavirus that emerged in 2019 and is now classified in the genus Coronavirus with closely related SARS-CoV. SARS-CoV-2 is highly pathogenic in humans and is classified as a biosafety level (BSL)-3 pathogen, which makes manipulating it relatively difficult due to its infectious nature. Methods:To circumvent the need for BSL-3 laboratories, an alternative assay was developed that avoids live virus and instead uses a recombinant VSV expressing luciferase and possesses the full length or truncated spike proteins of SARS-CoV-2. Furthermore, to measure SARS-CoV-2 neutralizing antibodies under BSL2 conditions, a chemiluminescence reduction neutralization test (CRNT) for SARS-CoV-2 was developed. The neutralization values of the serum samples collected from hospitalized patients with COVID-19 or SARS-CoV-2 PCR-negative donors against the pseudotyped virus infection evaluated by the CRNT were compared with antibody titers determined from an immunofluorescence assay (IFA). Results:The CRNT, which used whole blood collected from hospitalized patients with COVID-19, was also examined. As a result, the inhibition of pseudotyped virus infection was specifically observed in both serum and whole blood and was also correlated with the results of the IFA. Conclusions:In conclusion, the CRNT for COVID-19 is a convenient assay system that can be performed in a BSL-2 laboratory with high specificity and sensitivity for evaluating the occurrence of neutralizing antibodies against SARS-CoV-2.
Subject(s)
Tumor Virus Infections , Severe Acute Respiratory Syndrome , COVID-19ABSTRACT
The major challenge of the COVID-19 health crisis is to identify the factors of susceptibility to SARS-Cov2 in order to adapt the recommendations to the populations and to reduce the risk of getting COVID-19 to the most vulnerable people especially those having chronic respiratory diseases (CRD) including cystic fibrosis (CF) and chronic pulmonary respiratory diseases (COPD). Airway epithelial cells (AEC) are playing a critical role in the immune response and in COVID-19 severity. SARS-CoV-2 infects the airways through ACE2 receptor and the host protease TMPRSS2 was shown to play a major role in SARS-CoV-2 infectivity. In this report we showed that Pseudomonas aeruginosa and its virulence factor flagellin (Fla-PA), a ligand of Toll-Like receptor 5 are able to increase TMPRSS2 expression in control and CF AEC. In contrast, no effect was observed with recombinant Salmonella typhimurium flagellin, used as an adjuvant in the clinical development of new vaccines against respiratory viruses. Considering the urgency of the health situation, this result is of major significance for patients with CRD (COPD, CF) which are frequently infected and colonized by P. aeruginosa during the course of the disease. In the general population, a P. aeruginosa ventilator-associated pneumonia in SARS-CoV-2 patients under intubation in intensive care units could be also deleterious and should be monitored with care.
Subject(s)
Respiratory Tract Diseases , Lung Diseases , Severe Acute Respiratory Syndrome , Cystic Fibrosis , Chronic Disease , COVID-19ABSTRACT
SARS-CoV-2 has rapidly transmitted worldwide and results in the COVID-19 pandemic. Spike glycoprotein on surface is a key factor of viral transmission, and has appeared a lot of variants due to gene mutations, which may influence the viral antigenicity and vaccine efficacy. Here, we used bioinformatic tools to analyze B-cell epitopes of prototype S protein and its 9 common variants. 12 potential linear and 53 discontinuous epitopes of B-cells were predicted from the S protein prototype. Importantly, by comparing the epitope alterations between prototype and variants, we demonstrate that B-cell epitopes and antigenicity of 9 variants appear significantly different alterations. The dominant D614G variant impacts the potential epitope least, only with moderately elevated antigenicity, while the epitopes and antigenicity of some mutants(V483A, V367F, etc.) with small incidence in the population change greatly. These results suggest that the currently developed vaccines should be valid for a majority of SARS-CoV-2 infectors. This study provides a scientific basis for large-scale application of SARS-CoV-2 vaccines and for taking precautions against the probable appearance of antigen escape induced by genetic variation after vaccination. Author SummaryThe global pandemic of SARS-CoV-2 has lasted for more than half a year and has not yet been contained. Until now there is no effective treatment for SARS-CoV-2 caused disease (COVID-19). Successful vaccine development seems to be the only hope. However, this novel coronavirus belongs to the RNA virus, there is a high mutation rate in the genome, and these mutations often locate on the Spike proteins of virus, the gripper of the virus entering the cells. Vaccination induce the generation of antibodies, which block Spike protein. However, the Spike protein variants may change the recognition and binding of antibodies and make the vaccine ineffective. In this study, we predict neutralizing antibody recognition sites (B cell epitopes) of the prototype S protein of SARS-COV2, along with several common variants using bioinformatics tools. We discovered the variability in antigenicity among the mutants, for instance, in the more widespread D614G variant the change of epitope was least affected, only with slight increase of antigenicity. However, the antigenic epitopes of some mutants change greatly. These results could be of potential importance for future vaccine design and application against SARS-CoV2 variants.
Subject(s)
Severe Acute Respiratory Syndrome , COVID-19ABSTRACT
We screened steroid compounds to obtain a drug expected to block host inflammatory responses and MERS-CoV replication. Ciclesonide, an inhaled corticosteroid, suppressed replication of MERS-CoV and other coronaviruses, including SARS-CoV-2, the cause of COVID-19, in cultured cells. The effective concentration (EC90) of ciclesonide for SARS-CoV-2 in differentiated human bronchial tracheal epithelial cells was 0.55 M. Ciclesonide inhibited formation of double membrane vesicles, which anchor the viral replication-transcription complex in cells. Eight consecutive passages of 43 SARS-CoV-2 isolates in the presence of ciclesonide generated 15 resistant mutants harboring single amino acid substitutions in non-structural protein 3 (nsp3) or nsp4. Of note, ciclesonide still suppressed replication of all these mutants by 90% or more, suggesting that these mutants cannot completely overcome ciclesonide blockade. These observations indicate that the suppressive effect of ciclesonide on viral replication is specific to coronaviruses, highlighting it as a candidate drug for the treatment of COVID-19 patients. ImportanceThe outbreak of SARS-CoV-2, the cause of COVID-19, is ongoing. To identify the effective antiviral agents to combat the disease is urgently needed. In the present study, we found that an inhaled corticosteroid, ciclesonide suppresses replication of coronaviruses, including beta-coronaviruses (MHV-2, MERS-CoV, SARS-CoV, and SARS-CoV-2) and an alpha-coronavirus (HCoV-229E) in cultured cells. The inhaled ciclesonide is safe; indeed, it can be administered to infants at high concentrations. Thus, ciclesonide is expected to be a broad-spectrum antiviral drug that is effective against many members of the coronavirus family. It could be prescribed for the treatment of MERS, and COVID-19.
Subject(s)
Coronavirus Infections , COVID-19ABSTRACT
Given the aggressive spread of COVID-19-related deaths, there is an urgent public health need to support the development of vaccine candidates to rapidly improve the available control measures against SARS-CoV-2. To meet this need, we are leveraging our existing vaccine platform to target SARS-CoV-2. Here, we generated cellular heat shock chaperone protein, glycoprotein 96 (gp96), to deliver SARS-CoV-2 protein S (spike) to the immune system and to induce cell-mediated immune responses. We showed that our vaccine platform effectively stimulates a robust cellular immune response against protein S. Moreover, we confirmed that gp96-Ig, secreted from allogeneic cells expressing full-length protein S, generates powerful, protein S polyepitope-specific CD4+ and CD8+ T cell responses in both lung interstitium and airways. These findings were further strengthened by the observation that protein-S -specific CD8+ T cells were induced in human leukocyte antigen (HLA)-A2-02-01 transgenic mice thus providing encouraging translational data that the vaccine is likely to work in humans, in the context of SARS-CoV-2 antigen presentation.
Subject(s)
COVID-19ABSTRACT
SARS-CoV-2 is a novel coronavirus that emerged in 2019 and is now classified in the genus Coronavirus with closely related SARS-CoV. SARS-CoV-2 is highly pathogenic in humans and is classified as a biosafety level (BSL)-3 pathogen, which makes manipulating it relatively difficult due to its infectious nature. To circumvent the need for BSL-3 laboratories, an alternative assay was developed that avoids live virus and instead uses a recombinant VSV expressing luciferase and possesses the full length or truncated spike proteins of SARS-CoV-2. Furthermore, to measure SARS-CoV-2 neutralizing antibodies under BSL2 conditions, a chemiluminescence reduction neutralization test (CRNT) for SARS-CoV-2 was developed. The neutralization values of the serum samples collected from hospitalized patients with COVID-19 or SARS-CoV-2 PCR-negative donors against the pseudotyped virus infection evaluated by the CRNT were compared with antibody titers determined from an immunofluorescence assay (IFA). The CRNT, which used whole blood collected from hospitalized patients with COVID-19, was also examined. As a result, the inhibition of pseudotyped virus infection was specifically observed in both serum and whole blood and was also correlated with the results of the IFA. In conclusion, the CRNT for COVID-19 is a convenient assay system that can be performed in a BSL-2 laboratory with high specificity and sensitivity for evaluating the occurrence of neutralizing antibodies against SARS-CoV-2.
Subject(s)
COVID-19ABSTRACT
Steroid compounds, which are expected to have dual functions in blocking host inflammation and MERS-CoV replication, were screened from a chemical library. Within this library, ciclesonide, an inhaled corticosteroid, suppressed human coronavirus replication in cultured cells, but did not suppress replication of respiratory syncytial virus or influenza virus. The effective concentration of ciclesonide to block SARS-CoV-2 (the cause of COVID-19) replication (EC90) was 6.3 M. After the eleventh consecutive MERS-CoV passage in the presence of ciclesonide, a resistant mutation was generated, which resulted in an amino acid substitution (A25V) in nonstructural protein (NSP) 15, as identified using reverse genetics. A recombinant virus with the mutation was also resistant to ciclesonide suppression of viral replication. These observations suggest that the effect of ciclesonide was specific to coronavirus, suggesting this is a candidate drug for treatment of patients suffering MERS or COVID-19.