Interaction and antiviral treatment of coinfection between SARS-CoV-2 and influenza in vitro

BACKGROUND

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has lasted for three years. Coinfection with seasonal influenza may occur resulting in more severe diseases. The interaction between these two viruses for infection and the effect of antiviral treatment remains unclear.

METHODS

A SARS-CoV-2 and influenza H1N1 coinfection model on Calu-3 cell line was established, upon which the simultaneous and sequential coinfection was evaluated by comparing the viral load. The efficacy of molnupiravir and baloxavir against individual virus and coinfection were also studied.

RESULTS

The replication of SARS-CoV-2 was significantly interfered when the influenza virus was infected simultaneously or in advance (p < 0.05). On the contrary, the replication of the influenza virus was not affected by the SARS-CoV-2. Molnupiravir monotherapy had significant inhibitory effect on SARS-CoV-2 when the concentration reached to 6.25 μM but did not show any significant anti-influenza activity. Baloxavir was effective against influenza within the dosage range and showed significant effect of anti-SARS-CoV-2 at 16 μM. In the treatment of coinfection, molnupiravir had significant effect for SARS-CoV-2 from 6.25 μM to 100 μM and inhibited H1N1 at 100 μM (p < 0.05). The tested dosage range of baloxavir can inhibit H1N1 significantly (p < 0.05), while at the highest concentration of baloxavir did not further inhibit SARS-CoV-2, and the replication of SARS-CoV-2 significantly increased in lower concentrations. Combination treatment can effectively inhibit influenza H1N1 and SARS-CoV-2 replication during coinfection. Compared with molnupiravir or baloxavir monotherapy, combination therapy was more effective in less dosage to inhibit the replication of both viruses.

CONCLUSIONS

In coinfection, the replication of SARS-CoV-2 would be interfered by influenza H1N1. Compared with molnupiravir or baloxavir monotherapy, treatment with a combination of molnupiravir and baloxavir should be considered for early treatment in patients with SARS-CoV-2 and influenza coinfection.

Virological and clinical outcomes in outpatients treated with baloxavir or neuraminidase inhibitors for A(H3N2) influenza: A multicenter study of the 2022-2023 season

While clinical trials have illuminated both the virological and clinical efficacy of baloxavir for influenza and post-treatment viral resistance, these aspects warrant further study in real-world settings. In response, we executed a prospective, observational study of the Japanese 2022-2023 influenza season. A cohort of 73 A(H3N2)-diagnosed outpatients-36 treated with baloxavir, 20 with oseltamivir, and 17 with other neuraminidase inhibitors (NAIs)-were analyzed. Viral samples were collected before and after administering an antiviral on days 1, 5, and 10, respectively. Cultured viruses were amplified using RT-PCR and sequenced to detect mutations. Fever and other symptoms were tracked via self-reporting diaries. In the baloxavir cohort, viral detection was 11.1% (4/36) and 0% (0/36) on day 5 and day 10, respectively. Two isolates from day 5 (5.6%, 2/36) manifested I38T/M-substitutions in the polymerase acidic protein (PA). For oseltamivir and other NAIs, viral detection rates were 60.0% (12/20) and 52.9% (9/17) on day 5, and 16.7% (3/18) and 6.3% (1/16) on day 10, respectively. No oseltamivir-resistant neuraminidase mutations were identified after treatment. Median fever durations for the baloxavir, oseltamivir, and other NAI cohorts were 27.0, 38.0, and 36.0 h, respectively, with no significant difference. Two patients harboring PA I38T/M-substitutions did not exhibit prolonged fever or other symptoms. These findings affirm baloxavir's virological and clinical effectiveness against A(H3N2) in the 2022-2023 season and suggest limited clinical influence of post-treatment resistance emergence.

Antiviral susceptibility of clade 2.3.4.4b highly pathogenic avian influenza A(H5N1) viruses isolated from birds and mammals in the United States, 2022

Clade 2.3.4.4b highly pathogenic avian influenza (HPAI) A(H5N1) viruses that are responsible for devastating outbreaks in birds and mammals pose a potential threat to public health. Here, we evaluated their susceptibility to influenza antivirals. Of 1,015 sequences of HPAI A(H5N1) viruses collected in the United States during 2022, eight viruses (∼0.8%) had a molecular marker of drug resistance to an FDA-approved antiviral: three adamantane-resistant (M2-V27A), four oseltamivir-resistant (NA-H275Y), and one baloxavir-resistant (PA-I38T). Additionally, 31 viruses contained mutations that may reduce susceptibility to inhibitors of neuraminidase (NA) (n = 20) or cap-dependent endonuclease (CEN) (n = 11). A panel of 22 representative viruses was tested phenotypically. Overall, clade 2.3.4.4b A(H5N1) viruses lacking recognized resistance mutations were susceptible to FDA-approved antivirals. Oseltamivir was least potent at inhibiting NA activity, while the investigational NA inhibitor AV5080 was most potent, including against NA mutants. A novel NA substitution T438N conferred 12-fold reduced inhibition by zanamivir, and in combination with the known marker N295S, synergistically affected susceptibility to all five NA inhibitors. In cell culture-based assays HINT and IRINA, the PA-I38T virus displayed 75- to 108-fold and 37- to 78-fold reduced susceptibility to CEN inhibitors, baloxavir and the investigational AV5116, respectively. Viruses with PA-I38M or PA-A37T showed 5- to 10-fold reduced susceptibilities. As HPAI A(H5N1) viruses continue to circulate and evolve, close monitoring of drug susceptibility is needed for risk assessment and to inform decisions regarding antiviral stockpiling.

Influenza antivirals and their role in pandemic preparedness

Effective antivirals provide crucial benefits during the early phase of an influenza pandemic, when vaccines are still being developed and manufactured. Currently, two classes of viral protein-targeting drugs, neuraminidase inhibitors and polymerase inhibitors, are approved for influenza treatment and post-exposure prophylaxis. Resistance to both classes has been documented, highlighting the need to develop novel antiviral options that may include both viral and host-targeted inhibitors. Such efforts will form the basis of management of seasonal influenza infections and of strategic planning for future influenza pandemics. This review focuses on the two classes of approved antivirals, their drawbacks, and ongoing work to characterize novel agents or combination therapy approaches to address these shortcomings. The importance of these topics in the ongoing process of influenza pandemic planning is also discussed.

Prescription factors influencing baloxavir prescription during the 2018/2019 and 2019/2020 seasons: a administrative database study in Japan

BACKGROUND

We aimed to evaluate the factors associated with baloxavir prescription in Japanese hospitals using a health insurance claim-based database (MDV analyzer), during the 2018/2019 and 2019/2020 influenza seasons. The MDV analyzer contains anonymized claims data from approximately 420 Diagnosis Procedure Combination hospitals, and does not contain data from clinics.

METHODS

Data were collected for influenza patients treated with anti-influenza drugs during the 2018/2019 and 2019/2020 influenza seasons. Multivariate analysis was used to identify factors associated with baloxavir prescription.

RESULTS

During the study period, 322,063 influenza patients were included for analyses. In multivariate analysis, children, female sex, inpatient, hospital bed capacity, and private hospitals were negatively associated with baloxavir prescription. Compared to elderly patients, the adjusted odds ratio (OR) for baloxavir prescription was 0.612 (95% confidence interval (CI), 0.587-0.637) in children aged 6-11 years, and 0.119 (95% CI, 0.111-0.128) in children aged 0-5 years. Compared to small hospitals (bed capacity, 20-299), the adjusted OR for baloxavir prescription was 0.559 (95% CI, 0.540-0.578) in large hospitals (bed capacity, ≥ 500).

CONCLUSION

Children, female sex, inpatient, hospital bed capacity, and private hospitals were negatively associated with baloxavir prescription.

Influenza A virus polymerase acidic protein E23R substitution is a marker of reduced susceptibility to baloxavir

In our ongoing efforts to identify baloxavir resistance markers, we demonstrated that the influenza A polymerase acidic (PA) protein E23R substitution is genetically stable, increases baloxavir EC₅₀ values (13- to 19-fold vs. wild-type), synergizes with PA I38T, and only modestly decreases viral fitness. E23R is, therefore, a potential threat to baloxavir treatment efficacy.

Comparison of Inconvenience Costs Between Influenza Antivirals for Japanese Pediatric Patients: A Conjoint Analysis of Parental Responses

Introduction

Certain drug characteristics, including dosage and form, are associated with either convenience or inconvenience for the patients taking them, and any inconvenience can be considered as a “cost” in disease treatment. Multiple antivirals are available for influenza in Japan, with various dosages and forms. This study evaluated the inconvenience costs associated with influenza antivirals for pediatric patients by using conjoint analysis on responses from their parents.

Methods

An online survey (May 2021) was conducted for parents whose child took antivirals for influenza at 6–11 years during the 3 years until March 2021. Attributes of the conjoint analysis were administration routes and formulation (tablet, capsule, dry syrup, or inhalant), duration of administration, frequency of administration per day, and out-of-pocket expenses. We assumed the efficacy and safety to be equivalent among the antivirals. A logistic regression model was applied to the analysis. We also asked parents about their recent experiences with antiviral treatment for their child.

Results

We collected responses from 3161 eligible individuals. The mean age (standard deviation) of the children when taking the antivirals and percentage of female children were 8.27 (1.63) years old and 53.2%, respectively. The tablet was the most preferred formulation; the inconvenience costs for each administration route and formulation, relative to the tablet as zero, were Japanese yen (JPY) 515 (US dollar 4.61, as of October 2021) for the inhalant, JPY 775 for the capsule, and JPY 804 for the dry syrup. The inconvenience costs for 5 days relative to 1 day and for twice a day relative to once a day were JPY 2150 and JPY 399, respectively.

Conclusion

Based on the conjoint analysis, a single-dose tablet antiviral was suggested to have the lowest inconvenience cost for pediatric patients.

Trial Registration

UMIN000044243.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12325-022-02062-z.

Combination of Baloxavir and Oseltamivir for Treatment of Severe Influenza Infection in Hematopoietic Cell Transplant Recipients: A Novel Treatment Strategy for a High-risk Population

Baloxavir, a cap-dependent endonuclease inhibitor, was recently approved for treatment of severe influenza infections. Combining baloxavir with oseltamivir has been proposed to increase the response rate. We report 2 hematopoietic cell transplant recipients with severe influenza infections who were treated with this combination and discuss possible reasons for their different responses.

Clinical and virological outcomes with baloxavir compared with oseltamivir in pediatric patients aged 6 to < 12 years with influenza: an open-label, randomized, active-controlled trial protocol

Background

Children with influenza virus infections are prone to complications and are common sources of influenza transmission. Baloxavir marboxil inhibits cap-dependent endonuclease and was approved for influenza treatment in adolescent, adult, and pediatric patients in Japan. The miniSTONE-2 study included pediatric patients with influenza (1 to < 12 years) and demonstrated similar median times to alleviation of signs and symptoms of influenza with a single dose of baloxavir granules (weight < 20 kg: 2 mg/kg, ≥ 20 kg: 40 mg) and oseltamivir. Although the baloxavir dose in miniSTONE-2 was higher than the Japanese-approved dose, baloxavir exposure in miniSTONE-2 was similar to Japanese pediatric patients who receive the Japanese-approved dose. This study will be the first randomized active-controlled study in pediatric patients with influenza using the Japanese-approved dose of baloxavir.

Methods

This is a multicenter, open-label, randomized, active-controlled trial in which 200 Japanese subjects aged 6 to < 12 years with influenza virus infection are randomly allocated (2:1) to a single dose of baloxavir at the approved dose in Japan (weight ≥ 10 to < 20 kg: 10 mg, ≥ 20 to  < 40 kg: 20 mg, ≥ 40 kg: 40 mg) or oseltamivir twice daily for 5 days. The primary clinical endpoint is the time to illness alleviation of influenza, from administration of baloxavir or oseltamivir until the following criteria were met and sustained for at least 21.5 h (24 h—10%): cough and nasal discharge/nasal congestion rated as absent or mild axillary body temperature < 37.5 °C. The primary analysis population is the intention-to-treat infected population, which includes all pediatric subjects who receive at least one dose of study drug and have confirmed influenza virus infection by reverse transcription-polymerase chain reaction. The safety population includes all subjects who receive at least one dose of study drug.

Discussion

No comparative studies have been conducted to confirm the efficacy and safety of baloxavir versus a comparator in pediatric patients with influenza infection in Japan. The outcomes from this trial will provide evidence on the efficacy and safety of baloxavir as an antiviral treatment option for Japanese pediatric patients with influenza infection. Trial registration Japan Registry of Clinical Trials: jRCTs011200011. Registered November 2020. (https://rctportal.niph.go.jp/en/).

Influenza polymerase inhibitor resistance: Assessment of the current state of the art - A report of the isirv Antiviral group

It is more than 20 years since the neuraminidase inhibitors, oseltamivir and zanamivir were approved for the treatment and prevention of influenza. Guidelines for global surveillance and methods for evaluating resistance were established initially by the Neuraminidase Inhibitor Susceptibility Network (NISN), which merged 10 years ago with the International Society for influenza and other Respiratory Virus Diseases (isirv) to become the isirv-Antiviral Group (isirv-AVG). With the ongoing development of new influenza polymerase inhibitors and recent approval of baloxavir marboxil, the isirv-AVG held a closed meeting in August 2019 to discuss the impact of resistance to these inhibitors. Following this meeting and review of the current literature, this article is intended to summarize current knowledge regarding the clinical impact of resistance to polymerase inhibitors and approaches for surveillance and methods for laboratory evaluation of resistance, both in vitro and in animal models. We highlight limitations and gaps in current knowledge and suggest some strategies for addressing these gaps, including the need for additional clinical studies of influenza antiviral drug combinations. Lessons learned from influenza resistance monitoring may also be helpful for establishing future drug susceptibility surveillance and testing for SARS-CoV-2.

Baloxavir-oseltamivir combination therapy inhibits the emergence of resistant substitutions in influenza A virus PA gene in a mouse model

Baloxavir marboxil (BXM) treatment-emergent polymerase acid (PA) I38X amino acid substitution (AAS) in the resistant variants of influenza viruses raise concerns regarding their emergence and spread. This study investigated the impact of 1 or 5 mg/kg BXM and 25 mg/kg oseltamivir phosphate (OS) (single or combination therapy) on the occurrence of resistance-related substitutions during the sequential lung-to-lung passages of AH1N1)pdm09 virus in mice. Deep sequencing analysis revealed that 67% (n = 4/6) of the population treated with BXM single therapy (1 or 5 mg/kg) possessed the treatment-emergent PA-I38X AAS variants (I38T, I38S, and I38V). Notably, BXM-OS combination therapy impeded PA-I38X AAS emergence. Although the doses utilized in the mouse model may not be directly translated into the clinically equivalent doses of each drugs, these findings offer insights toward alternative therapies to mitigate the emergence of influenza antiviral resistance.

Open-label study of the safety, pharmacokinetics, and effectiveness of a 2 mg/kg dose of baloxavir marboxil 2% granules in children <20 kg with influenza

INTRODUCTION

Baloxavir marboxil is an oral anti-influenza drug with demonstrated safety and efficacy in pediatric patients when a 2% granules formulation is administered at 1 mg/kg. This study assessed safety, effectiveness, and pharmacokinetics of a higher dose (2 mg/kg) of baloxavir marboxil 2% granules in pediatric patients weighing <20 kg.

METHODS

This multicenter, open-label, noncontrolled study was conducted at 15 sites in Japan (January 2019-March 2020; JapicCTI-194577). Patients aged <12 years with confirmed influenza received a single oral dose of baloxavir marboxil at 2 mg/kg if body weight was <10 kg or 20 mg if ≥ 10 to <20 kg. Safety, pharmacokinetics, effectiveness (time to illness alleviation [TTIA] of influenza; time to resolution of fever; virus titer), and polymerase acidic protein (PA) substituted viruses were assessed over 22 days.

RESULTS

45 patients, all aged ≤6 years, were enrolled. Adverse events were reported in 24 (53.3%) patients, most commonly nasopharyngitis, diarrhea, and upper respiratory tract infection. Median (95% confidence interval [CI]) TTIA was 37.8 (27.5-46.7) hours; median (95% CI) time to resolution of fever was 22.0 (20.2-28.6) hours. A >4 log decrease in mean viral titer occurred at day 2 and a subsequent temporary 1-2 log increase in patients with influenza A(H3N2) and B. Treatment-emergent PA/I38X-substituted virus was detected in 16/39 (41.0%) patients, but no prolonged TTIA or time to resolution of fever was associated with its presence.

CONCLUSIONS

Baloxavir granules administered at 2 mg/kg in children <20 kg were well tolerated, with symptom alleviation similar to 1 mg/kg.

Virological and clinical outcomes in outpatients treated with baloxavir or oseltamivir: A Japanese multicenter study in the 2019-2020 influenza season

Although the virological and clinical efficacies of baloxavir for influenza and the post-treatment emergence of variant viruses have been reported in clinical trials, its efficacies have not been fully investigated in clinical settings. This prospective, observational investigator-initiated study was conducted during the 2019-2020 Japanese influenza season. In outpatients receiving baloxavir or oseltamivir, nasopharyngeal samples were obtained on day 1 before treatment and on the scheduled days 5 and 10 after treatment. RT-PCR and sequencing were performed to detect polymerase acidic protein (PA) E23X/I38X and neuraminidase (NA) H275Y variants in clinical and cultivated samples. Fever and illness-related symptoms were recorded using self-reporting diaries. Overall, 116 outpatients, 76 treated with baloxavir (34 under 12 years) and 40 with oseltamivir (32 under 12 years), were eligible. Of these, 91 were infected with A (H1N1)pdm09 (78.4%), of which 58 received baloxavir and 33 received oseltamivir. PA variants were detected in clinical (1.7%, 1/58; 3.8%, 1/26 for children under 12 years) and isolated (3.4%, 2/58; 3.8%, 1/26 for children under 12 years) samples obtained on day 5 after baloxavir treatment, but not on day 10. The isolation frequencies of A (H1N1)pdm09 on days 5 and 10 after baloxavir treatment were 5.2% (3/58) and 0.0% (0/58), respectively. Of the three viruses isolated on day 5, two (66.7%, 2/3) were PA I38 T/F variants with reduced baloxavir susceptibility. The isolation frequencies of A (H1N1)pdm09 on days 5 and 10 after oseltamivir treatment were 30.3% (10/33) and 6.1% (2/33), respectively. Only the two viruses isolated on day 10 were NA H275Y variants. The median duration of fever in baloxavir and oseltamivir recipients was 22.3 and 27.5 h, respectively. No patients with PA or NA variants showed prolonged durations of fever. Baloxavir was virologically effective for influenza in the clinical setting of the 2019-2020 Japanese season. Variant emergence after baloxavir treatment was limited to the early post-treatment stage.

Clinical efficacy and safety of baloxavir marboxil in the treatment of influenza: A systematic review and meta-analysis of randomized controlled trials

PURPOSE

The aim of this meta-analysis is to compare the clinical efficacy and safety of baloxavir with other anti-influenza agents or placebo in the treatment of influenza.

METHODS

PubMed, Embase, Web of Science, Google Scholar, Scopus, CINAHL, Cochrane databases and clinical registration were searched from inception until February 15 2021 for relevant randomized controlled trials (RCTs). Only phase 3 RCTs evaluating the usefulness of baloxavir in the treatment of influenza were included.

RESULTS

Three RCTs enrolling 3771 patients (baloxavir group, n = 1451; oseltamivir group, n = 1288; placebo group, n = 1032) were included. Compared with oseltamivir, baloxavir had an insignificantly shorter time to the alleviation of symptoms (mean difference [MD], -1.29 h; 95% CI, -6.80 to 4.21; I² = 0%). In contrast, baloxavir had a significantly shorter time to the alleviation of symptoms than placebo (MD, -26.32 h; 95% CI, -33.78 to -18.86; I² = 0%). Baloxavir was associated with a significant decline in influenza virus titers and viral RNA load compared to oseltamivir and placebo. Baloxavir was associated with a lower risk of any adverse events than oseltamivir (OR, 0.82; 95% CI, 0.69-0.98; I² = 0%) and placebo (OR, 0.79; 95% CI, 0.66-0.96; I² = 0%).

CONCLUSIONS

The findings of this meta-analysis suggested that baloxavir is superior to placebo in the treatment of influenza in both clinical outcome and virological response. Moreover, baloxavir was found to have a better virological response than oseltamivir and to be as effective as oseltamivir clinically. Compared with oseltamivir and placebo, baloxavir appears to be a relatively safe anti-influenza agent.

Burden of influenza B virus infection and considerations for clinical management

Influenza B viruses cause significant morbidity and mortality, particularly in children, but the awareness of their impact is often less than influenza A viruses partly due to their lack of pandemic potential. Here, we summarise the biology, epidemiology and disease burden of influenza B, and review existing data on available antivirals for its management. There has long been uncertainty surrounding the clinical efficacy of neuraminidase inhibitors (NAIs) for influenza B treatment. In this article, we bring together the existing data on NAIs and discuss these alongside recent large randomised controlled trial data for the new polymerase inhibitor baloxavir in high-risk influenza B patients. Finally, we offer considerations for the clinical management of influenza B, with a focus on children and high-risk patients where disease burden is highest.

Influenza A(H1N1)pdm09 virus exhibiting reduced susceptibility to baloxavir due to a PA E23K substitution detected from a child without baloxavir treatment

Human-to-human transmission of PA I38 mutant influenza A(H3N2) viruses with reduced baloxavir susceptibility has been reported in Japan. In December 2019, we detected a PA E23K mutant A(H1N1)pdm09 virus from a child without baloxavir treatment. The PA E23K mutant virus exhibited reduced baloxavir susceptibility but remained susceptible to neuraminidase inhibitors. Epidemiological data suggest possible transmission of this PA E23K mutant virus among humans, although its growth capability relative to that of the wild-type virus was reduced. Therefore, baloxavir susceptibility monitoring of influenza viruses is essential.

Safety and effectiveness of baloxavir marboxil for the treatment of influenza in Japanese clinical practice: A postmarketing surveillance of more than 3000 patients

Baloxavir marboxil is an oral anti-influenza drug that inhibits the cap-dependent endonuclease of the virus polymerase acidic protein. In clinical trials, baloxavir reduced the time to alleviation of influenza symptoms and time to resolution of fever in adults, adolescents, and children. The purpose of this study is to collect data on the safety and effectiveness of baloxavir when used in clinical practice. This postmarketing surveillance (clinicaltrials.jp; JapicCTI-183882), conducted at 688 Japanese hospitals or clinics (March 2018 to March 2019), enrolled patients of any age with influenza A or B infection who received a single, weight-based dose of baloxavir. Adverse drug reactions (ADRs) were seen in 11.2% of 3094 patients during the 7-day observation period; the most common ADR was diarrhea (6.1%). ADRs were more common in children aged <12 years (14.1%) than in adults (10.0%). Almost all ADRs were non-serious (98.9%) and were recovered or recovering (96.7%). Median time to alleviation of symptoms (N = 2884) was 2.5 days (overall, influenza A, and influenza B groups). Median time to resolution of fever (N = 2946) was 1.5 days (overall, influenza A, and influenza B groups). Biphasic fever (increased temperature after previous fever resolution) was seen in 6.7% of patients overall and 28.6% of patients <6 years infected with influenza B, similar to rates published elsewhere with other influenza drugs and in untreated influenza. This postmarketing surveillance of >3000 patients suggests that baloxavir is well tolerated and effective regardless of patient age or influenza virus type.

Early combination treatment with baloxavir and peramivir for hospitalized adults with influenza A in Yokohama, Japan

Baloxavir marboxil is a new anti-influenza drug, but data on the clinical efficacy of a combination treatment of baloxavir and peramivir is scarce. We conducted a single-center retrospective analysis comparing the mortality of a combination of baloxavir and peramivir (B & P, n = 10) and peramivir without baloxavir (P-mono, n = 132) in hospitalized adults with influenza A between 2011 and 2019 in Yokohama City, Japan. Sequencing analysis was conducted in the B & P group to check the I38 mutation in polymerase acidic protein which is associated with baloxavir resistance. The 30-day mortality rates were 0 (0%) in the B & P group and 6 (4.5%) in the P-mono group, respectively, which was not statistically significant. The I38 mutation was not detected before and after the combination treatment. A combination treatment of baloxavir and peramivir might be more effective than peramivir without baloxavir and prevent the emergence of baloxavir resistance in hospitalized adults with influenza A.

Global update on the susceptibilities of human influenza viruses to neuraminidase inhibitors and the cap-dependent endonuclease inhibitor baloxavir, 2017-2018

The global analysis of neuraminidase inhibitor (NAI) susceptibility of influenza viruses has been conducted since the 2012-13 period. In 2018 a novel cap-dependent endonuclease inhibitor, baloxavir, that targets polymerase acidic subunit (PA) was approved for the treatment of influenza virus infection in Japan and the United States. For this annual report, the susceptibilities of influenza viruses to NAIs and baloxavir were analyzed. A total of 15409 viruses, collected by World Health Organization (WHO) recognized National Influenza Centers and other laboratories between May 2017 and May 2018, were assessed for phenotypic NAI susceptibility by five WHO Collaborating Centers (CCs). The 50% inhibitory concentration (IC₅₀) was determined for oseltamivir, zanamivir, peramivir and laninamivir. Reduced inhibition (RI) or highly reduced inhibition (HRI) by one or more NAIs was exhibited by 0.8% of viruses tested (n = 122). The frequency of viruses with RI or HRI has remained low since this global analysis began (2012-13: 0.6%; 2013-14: 1.9%; 2014-15: 0.5%; 2015-16: 0.8%; 2016-17: 0.2%). PA gene sequence data, available from public databases (n = 13523), were screened for amino acid substitutions associated with reduced susceptibility to baloxavir (PA E23G/K/R, PA A36V, PA A37T, PA I38F/M/T/L, PA E119D, PA E199G): 11 (0.08%) viruses possessed such substitutions. Five of them were included in phenotypic baloxavir susceptibility analysis by two WHO CCs and IC₅₀ values were determined. The PA variant viruses showed 6-17-fold reduced susceptibility to baloxavir. Overall, in the 2017-18 period the frequency of circulating influenza viruses with reduced susceptibility to NAIs or baloxavir was low, but continued monitoring is important.

The Cap-Snatching SFTSV Endonuclease Domain Is an Antiviral Target

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne virus with 12%-30% case mortality rates and is related to the Heartland virus (HRTV) identified in the United States. Together, SFTSV and HRTV are emerging segmented, negative-sense RNA viral (sNSV) pathogens with potential global health impact. Here, we characterize the amino-terminal cap-snatching endonuclease domain of SFTSV polymerase (L) and solve a 2.4-Å X-ray crystal structure. While the overall structure is similar to those of other cap-snatching sNSV endonucleases, differences near the C terminus of the SFTSV endonuclease suggest divergence in regulation. Influenza virus endonuclease inhibitors, including the US Food and Drug Administration (FDA) approved Baloxavir (BXA), inhibit the endonuclease activity in in vitro enzymatic assays and in cell-based studies. BXA displays potent activity with a half maximal inhibitory concentration (IC50) of ∼100 nM in enzyme inhibition and an EC50 value of ∼250 nM against SFTSV and HRTV in plaque assays. Together, our data support sNSV endonucleases as an antiviral target.

Effective Anti-SARS-CoV-2 RNA Dependent RNA Polymerase Drugs Based on Docking Methods: The Case of Milbemycin, Ivermectin, and Baloxavir Marboxil

BACKGROUND

Severe Acute Respiratory Syndrome-coronavirus 2 (SARS-CoV-2) is a new virus with a global pandemic. Yet, no vaccine or efficient treatments are found against the disease. The viral RNA dependent RNA Polymerase (RdRP) is a suitable target for developing antiviral agents. SARS-CoV-2 RdRP was employed to test its binding activity with some drugs.

METHODS

Using some docking methods, RdRP was targeted by Milbemycins (MMs), Ivermectin (IMT), Baloxavir Marboxil (BM), and Tadalafil (TF), a phosphodiesterase type 5 inhibitor.

RESULTS

MM-A3 5-oxime (MMA35O), MM-A3 (MMA3), MM-A4 5-oxime (MMA45O), IMT, BM, and TF showed the highest binding affinity to RdRp.

CONCLUSION

The drugs used in the present computational investigation are effective against the SARS-CoV-2 RdRP with high affinity values especially, milbemycins, ivermectin, and Baloxavir marboxil, which could further be studied in laboratory and clinical trials for saving millions of lives around the world.

Adult influenza A (H3N2) with reduced susceptibility to baloxavir or peramivir cured after switching anti-influenza agents

We describe two adults with A/H3N2 influenza with (patient 1), and without (patient 2) polymerase acidic (PA) subunit I38 T substitution during the same season. Patient 1 had a reduced clinical response to baloxavir, a cap-dependent endonuclease inhibitor (CEI), but was cured by peramivir, a neuraminidase inhibitor. Baloxavir was clinically effective for patient 2, for whom peramivir had been ineffective. Susceptibility to baloxavir can be decreased by a PA unit mutation, but response to treatment can be increased by switching and/or combination with a neuraminidase inhibitor, even though CEI are clinically effective against influenza in adults.

A network meta-analysis of the efficacy and safety of baloxavir marboxil versus neuraminidase inhibitors for the treatment of influenza in otherwise healthy patients

Objective: Baloxavir marboxil (baloxavir) is the first cap-dependent endonuclease inhibitor being studied for the treatment of influenza in single oral dosing regimen. This network meta-analysis (NMA) evaluated the efficacy and safety of baloxavir compared to other antivirals for influenza in otherwise healthy patients. Methods: A systematic literature review was performed on 14 November 2016 in Medline, Embase, CENTRAL, and ICHUSHI to identify randomized controlled trials assessing antivirals for influenza. A NMA including 22 trials was performed to compare the efficacy and safety of baloxavir with other antivirals. Results: The time to alleviation of all symptoms was significantly shorter for baloxavir compared to zanamivir (difference in median time 19.96 h; 95% CrI [3.23, 39.07]). The time to cessation of viral shedding was significantly shorter for baloxavir than zanamivir and oseltamivir (47.00 h; 95% CrI [28.18, 73.86] and 56.03 h [33.74, 87.86], respectively). The mean decline in virus titer from baseline to 24 h was significantly greater for baloxavir than for the other drugs. Other differences in efficacy outcomes were not significant. No significant differences were found between baloxavir and the other antivirals for safety, except total drug-related adverse events where baloxavir demonstrated a decrease compared to oseltamivir and laninamivir. Conclusions: The NMA suggests that baloxavir demonstrated better or similar efficacy results compared to other antivirals with a comparable safety profile. Baloxavir led to a significant decrease in viral titer versus zanamivir, oseltamivir and peramivir and decreased viral shedding versus zanamivir and oseltamivir.

Investigational antiviral therapies for the treatment of influenza

INTRODUCTION

Influenza viral ribonucleoprotein complexes (vRNPs) play a key role in viral transcription and replication; hence, the recent development of novel anti-influenza drugs targeting vRNPs has garnered widespread interest.

AREAS COVERED

We discuss the function of the constituents of vRNPs and summarize those vRNPs-targeted synthetic drugs that are in preclinical and early clinical development.

EXPERT OPINION

vRNPs contain high-value drug targets; such targets include the subunits PA, PB1, PB2, and NP. Developing a new generation of antiviral therapies with strategies that utilize existing drugs, natural compounds originated from new resources and novel drug combinations may open up new therapeutic approaches to influenza.