Use of #baloxavir as adjunctive #antiviral #therapy to neuraminidase inhibitors in severely immunocompromised individuals infected with #influenza

 

ABSTRACT

Immunocompromised patients are at risk of developing severe influenza, with protracted viral shedding and development of resistance-associated mutations under antiviral treatment. We report a case series of severely immunocompromised hematology patients, including allogeneic hematopoietic cell transplantation (HCT) recipients, treated with both baloxavir and oseltamivir and describe clinical and virological outcomes and the safety profile of prolonged combination therapy. Allogeneic HCT recipients with influenza infection treated with baloxavir were retrieved via institutional databases. All hospitalized allogeneic HCT patients treated with a combination therapy of baloxavir and oseltamivir over five influenza seasons between October 2019 and May 2025 were included. Six influenza-infected hematology patients (5/6 allogeneic HCT recipients) were treated with combination therapy of oseltamivir and baloxavir. All patients presented with lower respiratory tract infections. Oseltamivir treatment duration ranged from 5 to 31 days, and the number of administered baloxavir doses ranged between one and five. Baloxavir administration was well tolerated, and no adverse events could be attributed to the administered antiviral treatment. All-cause mortality at 3 months post-infection was 66% (4/6), mainly driven by underlying disease. In two patients with protracted shedding, combination therapy did not prevent the development of resistance mutation(s). Combination treatment with prolonged courses of oseltamivir and repeated doses of baloxavir was well tolerated. No definitive conclusions on the efficacy of this approach could be drawn from this study. More data are required on the best treatment of hematology patients infected with influenza.

Source: 

Link: https://journals.asm.org/doi/10.1128/aac.01659-25

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#Oseltamivir aziridines are potent #influenza #neuraminidase #inhibitors and imaging agents

 

Significance

Influenza remains a major global health threat. We introduce oseltamivir-based aziridines that unite transition-state mimicry for tight binding with aziridine-enabled covalent capture of the catalytic tyrosine. This dual function yields potent, mechanism-based neuraminidase inhibition and enables activity-based quantification of active enzyme directly in complex samples. Across N1, N2, and influenza B enzymes, selected compounds show high potency against diverse viral neuraminidases and in live virus replication assays. By combining a clinically grounded scaffold with a reactivity handle, these molecules bridge therapeutic and diagnostic needs and offer a practical platform for neuraminidase imaging and antiviral development.

Abstract

Influenza neuraminidase (NA) is a critical target for seasonal and pandemic antivirals, including the strains of current concern. Current treatments, such as Zanamivir and Oseltamivir, are limited by noncovalent binding and emerging resistance. We hypothesized that Oseltamivir aziridines would unite transition-state mimicry for tight binding, with aziridine-enabled covalent capture of the catalytic tyrosine, thereby supporting both therapy and activity-based quantification. Here, we present oseltamivir-based aziridines, inspired by cyclophellitol chemistry, that act as covalent inhibitors and activity-based probes via an N-acylaziridine warhead. Free-energy calculations, and NMR observations, indicate a 4H5 half-chair preference consistent with the NA transition state, and selected analogues inhibit multiple NA subtypes with low nanomolar binding constants. Diverse evidence establishes covalency: time-dependent inactivation, inhibitor washout, intact-mass shifts, MS/MS identification of a tyrosine adduct, and QM/MM reaction profiles, while cryoEM of N1 aligns with the proposed binding mode, revealing an elimination product. The inhibitors demonstrate formidable activity against diverse viral neuraminidases, including H5N1, and further enable imaging and quantification of active NA. With their dual therapeutic and diagnostic potential, these first-in-class inhibitors indeed benefit from transition state mimicry and covalency, and thus offer a powerful platform for antiviral development and neuraminidase imaging, addressing urgent global health needs in influenza treatment and prevention.

Source: 

Link: https://www.pnas.org/doi/10.1073/pnas.2504045123

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14th Meeting of #WHO #Expert Working Group of the Global #Influenza #Surveillance and Response System (GISRS) for Surveillance of #Antiviral Susceptibility (March 20 '26)

Weekly epidemiological record 

20 MARCH 2026, 101th YEAR, No 12, 2026, 101, 53–56

http://www.who.int/wer 

Executive Summary 

The WHO Expert Working Group on Surveillance of Influenza Antiviral Susceptibility (AVWG) supports the WHO GISRS by providing practical guidance for monitoring antiviral susceptibility of seasonal and emerging influenza viruses through global surveillance efforts. 

The 14th WHO-AVWG meeting was held in virtual format on 10-12 June 2025. 

Update on susceptibility of seasonal influenza viruses to approved antiviral agents 

From approximately May 2024 to May 2025, five WHO Collaborating Centres (CCs) and two National Influenza Centres (NICs) reported co-circulation of influenza A(H1N1) pdm09, A(H3N2), and B/Victoria viruses. 

A(H1N1)pdm09 dominated in Eastern Asia{1}. Elevated frequency of influenza neuraminidase (NA) inhibitor (NAI) reduced inhibition/ highly reduced inhibition (RI/HRI) was identified among A(H1N1)pdm09 viruses, largely conferred by the NA-H275Y substitution. 

Reporting frequency was 3.8% in China, lower (≤1%) in other reporting regions, but still measurable and were in some cases a result of prior antiviral use or specific local outbreaks (e.g., a hospital in Iceland with a NA-H275Y+S247N cluster, a primary school classroom outbreak in Japan{2}. The NA-S247N substitution (≤3.3%) was also noted by three centres, but these viruses exhibited normal inhibition (NI) by NAIs when available isolates were tested. 

Incidence of RI/HRI or NA-associated markers were less frequently reported for A(H3N2) and B/Victoria viruses than A(H1N1)pdm09 viruses. 

Markers and incidence of reduced susceptibility to baloxavir was detected at low frequencies of 0.07 to 2.2%, where the latter value represented a small sample set of only 2 of 89 viruses in Japan. 

Reduced susceptibility or amino acid markers indicative of reduced susceptibility were observed only in influenza A viruses and not influenza B. 

Update on susceptibility of zoonotic and animal influenza viruses  to approved antiviral agents 

From approximately May 2024 to May 2025, global surveillance data from WHO CCs, NICs, and associated partners including WHO Essential Regulatory Laboratories and the OFFLU (WOAH/FAO Network of Expertise on Animal Influenza) network reported that most zoonotic and avian influenza viruses, particularly circulating A(H5N1/x) HA clade 2.3.4.4b and 2.3.2.1a/e viruses, were broadly susceptible to NAIs and baloxavir. 

A(H5N1) 2.3.4.4b virus oseltamivir inhibitory concentrations remain elevated vs. seasonal N1 viruses. 

Small and isolated incidence of NAI associated RI/HRI or markers included: NA-D199G mediated oseltamivir/zanamivir RI detected in A(H5N1) 2.3.4.4b poultry in the Russian Federation (February 2024, reported June 2025), NA-N295S in poultry in India A(H5N1) 2.3.2.1a isolates, and 8 poultry farms in British Columbia, Canada exhibiting A(H5N1) 2.3.4.4b with NA-H275Y. 

Only two viruses with reduced baloxavir susceptibility were identified, 1 human virus with PA-I38M (California, USA) and 1 environmental virus isolate with PA-V100I (China, Hong Kong Special Administrative Region). 

Beyond A(H5N1/x), nearly 30 avian influenza subtypes including A(H9N2), A(H7N2), A(H7N7), and A(H7N9), and A(H10N7) were analysed across surveillance sites in the Bangladesh, Egypt, the Netherlands and the United States of America (USA). 

They generally lacked NA or PA genotypic markers of reduced drug susceptibility and when available for phenotypic testing, were susceptible to both NAIs and baloxavir. 

A(H7N2) and A(H7N7) viruses from the Netherlands displayed oseltamivir RI compared to human seasonal references, but this may be due to foldchange comparison to a mismatched NA subtype. 

Swine-origin variant viruses (A(H1N1)v, A(H1N2)v, A(H3N2)v) tested across the USA and Europe were largely free of genotypic or phenotypic indicators of reduced susceptibility/inhibition to NAIs or baloxavir. 

Some viruses (the  Netherlands) showed slightly higher NAI median inhibitory concentrations to historical or human seasonal baselines, but all remained below NAI RI thresholds. 

Update of protocols and guidance for GISRS laboratories 

Both genotypic and phenotypic assays may be used as tools to monitor susceptibility of influenza viruses to NAIs and baloxavir. 

The WHO-AVWG routinely reviews and updates influenza NA and PA amino acid substitutions associated with reduced susceptibility to NAIs and baloxavir; updated tables for the previous reporting period were included on the WHO website{3–5}. 

The US CDC continues to update and ship reference virus panels that can be used for NAI and baloxavir susceptibility testing, available via the International Reagent Resource{6} 

Further guidance on baloxavir and other PA inhibitor testing included the Influenza Replication Inhibition Neuraminidase-based Assay (IRINA), published by the Centers for Disease Control and Prevention, USA{7} and included on the WHO website{8}. 

The WHO AVWG continues to develop algorithms for NICs to aid in influenza response planning (zoonotic, pandemic, and antiviral resistance-specific events), guidance to aid in decisions making for testing strategies (genotypic vs. phenotypic), and guidance for consideration of baloxavir and PA inhibitor specific amino acid substitutions associated with reduced drug susceptibility{9}. 

Additionally, the WHO-AVWG has worked with GISAID to continue to refine and implement modifications to existing tools to facilitate identification of NA and PA substitutions upon sequence submission. 

Outbreak and pandemic preparedness with clinicians’ perspectives 

Two physicians, Profs. Prof. David Hui and Bin Cao, were invited to present recently updated WHO guidance on clinical practice guidelines for influenza{10}. 

Significant updates and discussion surrounded inclusion of baloxavir, which was conditionally recommended for non-severe disease high-risk patients and post-virus exposure prophylaxis (PEP) including influenza viruses associated with high mortality. 

Conditional recommendation against any NAI or baloxavir intervention remains for non-severe disease low-risk patients or seasonal virus PEP. 

Data was presented on multiple PA inhibitors rapidly moving through late-stage clinical trials in China which may have implications on expanded usage of this newer class of influenza drugs. 

Review of External Quality Assessment Programme (EQAP) panels 

EQAP was initiated in 2007 to monitor the quality of GISRS, NICs, other national influenza reference laboratories’ capacity for influenza diagnosis and detection. 

An optional antiviral phenotypic NAI panel was introduced in 2013, and genotypic baloxavir susceptibility was introduced in 2020. 

Results for the 2024 Global EQAP panel were reported during the 14th WHO-AVWG meeting. 

Of the 194 participating laboratories, 26.3% participated in NAI susceptibility testing. 

Results and subsequent discussion from this year’s panel were used by members of WHO-AVWG to assess the training needs of NICs. 

Way forward 

The 2020–2023 Annual Global Update on the Susceptibility of Influenza Viruses (Global AVS) manuscript was published{11} and drafting of a 2023–2025 publication is underway. The next WHO-AVWG meeting will be held in June 2026.

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{1} World Health Organization. Influenza Transmission Zones. 2026. https://cdn.who.int/media/docs/ default-source/influenza/influenzaupdates/2025_09_24_influenza-transmission-zones. pdf?sfvrsn=22361408_3&download=true. 

{2} Takashita E, Shimizu K, Usuku S, Senda R, Okubo I, Morita H, et al. An outbreak of influenza A(H1N1) pdm09 antigenic variants exhibiting cross-resistance to oseltamivir and peramivir in an elementary school in Japan, September 2024. Euro Surveill. 2024;29(50).

{3} World Health Organization. Summary of neuraminidase (NA) amino acid substitutions assessed for their effects on inhibition by neuraminidase inhibitors (NAIs). 2025. https://cdn.who.int/media/docs/default-source/ influenza/laboratory---network/quality-assurance/human-nai-marker-table_ for-publication_final_20240918.pdf. 

{4} World Health Organization. Summary of neuraminidase (NA) amino acid substitutions assessed for their effects on inhibition by NA inhibitors (NAIs) among avian influenza viruses of Group 1 (N1, N4, N5, N8 subtypes) and Group 2 (N2, N3, N6, N7, N9 subtypes) NAs. 2025. https://cdn.who.int/media/ docs/default-source/influenza/avwg/avian-nai-marker-whotable__10-10-2025.pdf?sfvrsn=bc0d1e9a_10 

{5} World Health Organization. Summary of polymerase acidic protein (PA) amino acid substitutions assessed for their effects on PA inhibitor (PAI) baloxavir susceptibility. 2025. https://cdn.who.int/media/docs/default-source/influenza/ laboratory---network/quality-assurance/antiviral-susceptibility-influenza/ pa-marker-who-table_28-11-2025_updated.pdf?sfvrsn=5307d6fe_4. 

{6} International Reagent Resource. 2026. https://www. internationalreagentresource.org/. 

{7} Patel MC, Flanigan D, Feng C, Chesnokov A, Nguyen HT, Elal AA, et al. An optimized cell-based assay to assess influenza virus replication by measuring neuraminidase activity and its applications for virological surveillance. Antiviral Res. 2022;208:105457. 

{8} World Health Organization. Baloxavir Susceptibility Assessment using Influenza Replication Inhibition Neuraminidase-based Assay (IRINA). https:// cdn.who.int/media/docs/default-source/influenza/avwg/cdc-phenotypic-lp492rev01d---baloxavir-susceptibility-assessment-using-irina.pdf? 

{9} Patel MC, Nguyen HT, Mishin VP, Pascua PNQ, Champion C, Lopez-Esteva M, et al. Antiviral susceptibility monitoring: testing algorithm, methods, and f indings for influenza season, 2023-2024. Antiviral Res. 2025;244:106299. 

{10} World Health Organization. Clinical practice guidelines for influenza 2024. https://www.who.int/publications/i/item/9789240097759.

{11} Hussain S, Meijer A, Govorkova EA, Dapat C, Gubareva LV, Barr I, et al. Global update on the susceptibilities of influenza viruses to neuraminidase inhibitors and the cap-dependent endonuclease inhibitor baloxavir, 2020-2023. Antiviral Res. 2025:106217.

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Source: 

Link: https://iris.who.int/server/api/core/bitstreams/1ea408da-cd90-438b-b80c-b00aaf4e7315/content

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Optimal Dose and #Safety of Intravenous #Favipiravir in Hospitalized Patients With #COVID19: A Dose-Escalating, Randomized Controlled Phase Ib Study

 

Abstract

AGILE (NCT04746183) is a Phase Ib/IIa platform, evaluating candidates to treat COVID-19. Candidate Specific Trial 6 evaluated the safety and optimal dose of a novel intravenous formulation of favipiravir in a dose-escalating, open-label, randomized, controlled, Bayesian adaptive Phase Ib trial. Hospitalized adults with PCR-confirmed SARS-CoV-2 infection, within 14 days of symptomatic COVID-19 were randomized 2:1 in groups of 6 (n = 4 favipiravir, n = 2 standard of care) to ascending doses of intravenous favipiravir twice daily (b.i.d.) for 7 days or standard of care. Clinical data, safety evaluations, virology and pharmacokinetic samples were collected. The primary outcome was safety. Secondary outcomes included clinical, pharmacokinetic and virological endpoints. Twenty-four participants enrolled between September 10, 2022 and November 1, 2023 [10/24 female; median age 74 years (range 52–93)]. Favipiravir was well tolerated despite a high background rate of unrelated adverse events. No dose limiting toxicities were observed, with a model-predicted dose limiting toxicity risk of 16.8% and probability of unacceptable toxicity of 2.7% at the highest dose level. No serious adverse events were deemed related to favipiravir but an expected association with asymptomatic, transient hyperuricemia was observed. Favipiravir exposures increased disproportionally to dose with significant accumulation in plasma, but with marked variability between participants within each cohort. This novel formulation of favipiravir was safe at sustained high doses that reached pre-specified pharmacokinetic targets in a study group with frailty and complex health profiles. We consider doses up to 2,400 mg b.i.d. to be safe for further evaluation.

Study Highlights

-- WHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC?

- Pre-clinical studies of favipiravir describe broad spectrum antiviral activity, positioning it as a therapeutic candidate for many RNA viruses. An oral formulation of favipiravir has been widely studied as a treatment for COVID-19 in clinical trials. Pharmacokinetic modeling suggests the doses used in many of these trials may not have reached effective plasma concentrations.

-- WHAT QUESTION DID THIS STUDY ADDRESS?

- Was a novel intravenous formulation of favipiravir safe and well tolerated in patients hospitalized with COVID-19? Were pre-specified pharmacokinetic parameters met at doses modeled to be effective for the treatment of COVID-19?

-- WHAT DOES THIS STUDY ADD TO OUR KNOWLEDGE?

- We demonstrate that high doses of intravenous favipiravir are safe and well tolerated in a frail and co-morbid population who are likely to be eligible for antiviral treatment but are often excluded from early phase clinical trials. We characterize the pharmacokinetic profile of intravenous favipiravir at high doses and recommend an optimal dose to be used in future Phase II studies.

-- HOW MIGHT THIS CHANGE CLINICAL PHARMACOLOGY OR TRANSLATIONAL SCIENCE?

- There is an ongoing unmet need for antivirals to effectively treat COVID-19; however, the significance of these safety and pharmacokinetic data go beyond COVID-19. High doses of favipiravir have a use case against RNA viruses with pandemic potential including viral hemorrhagic fevers and pandemic influenza. The intravenous formulation may be particularly relevant in severely unwell patients for whom oral dosing is not possible or in whom GI absorption is affected. The pharmacokinetic characterization from this study will be used to inform doses for use against a range of significant pathogens. Early phase clinical trials of IV favipiravir in Crimean-Congo Haemorrhagic Fever are ongoing.

Source: 

Link: https://ascpt.onlinelibrary.wiley.com/doi/10.1002/cpt.70261

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A #clinical #SARS-CoV-2 #Mpro #inhibitor blocks replication of multiple #enteroviruses and confers oral in vivo protection in animal models

 

Abstract

Enteroviruses, which belong to the family Picornaviridae, cause hand, foot, and mouth disease (HFMD), respiratory symptoms, and severe neurological complications in children. Since vaccines cannot provide cross-protection against different serotypes of enteroviruses, the development of broad-spectrum anti-enteroviral drugs is imperative. The viral 3C protease (3Cpro), which is essential for polyprotein processing represents a validated target for therapeutic intervention. Importantly, enterovirus 3Cpro shares conserved structural and catalytic features with coronavirus main protease (Mpro, also known as 3C-like protease, 3CLpro), providing a rationale for cross-target inhibitor repurposing. Through targeted screening of peptidomimetic protease inhibitors, a clinical-stage SARS-CoV-2 Mpro inhibitor was identified as a potent inhibitor of enterovirus A71 (EV71) 3Cpro. Bofutrelvir displayed nanomolar antiviral activity in multiple cell lines and demonstrated broad-spectrum efficacy against several enteroviruses including coxsackievirus B5, coxsackievirus A16 (CA16) and echovirus 11. In EV71 infected neonatal mice, intraperitoneal administration of bofutrelvir markedly reduced viral loads in brain, spinal cord, and muscle, alleviated clinical symptoms, and suppressed tissue inflammation. Oral administration of bofutrelvir also provided therapeutic benefits in neonatal mice models of both EV71 and CA16. Crystallographic analysis revealed that bofutrelvir binds in the conserved substrate-binding cleft of EV71 3Cpro, elucidating its molecular mechanism of inhibition. These findings identify bofutrelvir as a broad-spectrum peptidomimetic 3Cpro inhibitor with strong antiviral efficacy against enteroviruses and highlight its potential for repurposing as a promising antiviral candidate for the treatment of enteroviral infections.

Source: 

Link: https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1014051

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#Zanamivir - #Amantadine Conjugate: A Dual-Action Agent with Broad-Spectrum Synergistic #Antiviral Efficacy

 

Abstract

Influenza A virus is a highly contagious respiratory pathogen, and its rapid and continuous adaptive mutations for immune escape have limited the efficacy of existing vaccines and antiviral drugs. Here, we report a multimechanism anti-influenza platform based on the conjugation of zanamivir (ZMV) with amantadine (Aman). Aman acts as a hydrophobic tag that promotes the degradation of neuraminidase and concurrently enhances the physicochemical properties of ZMV, leading to improved membrane permeability and a significantly prolonged half-life. Meanwhile, the ZMV moiety counteracts Aman-induced cytotoxic autophagy. The resulting conjugate, compound 7j, exhibits potent activity against a wide range of neuraminidase and M2 ion channel mutations. Notably, a single intravenous dose of 7j fully protected mice from a lethal H1N1 challenge. Our work demonstrates that the rational fusion of ZMV and Aman achieves synergistic multimechanistic antiviral activity with enhanced efficacy and safety, offering a new strategy for the development of next-generation anti-influenza drugs.

Source: 

Link: https://pubs.acs.org/doi/10.1021/acs.jmedchem.5c03547

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#Tecovirimat for the Treatment of #Mpox

 

Abstract

Background

Tecovirimat is approved for smallpox treatment under the Food and Drug Administration Animal Rule on the basis of efficacy in nonhuman primate models of mpox (previously known as monkeypox). However, the clinical efficacy of tecovirimat against human clade II mpox is unclear.

Methods

In a phase 3, international, double-blind, randomized, placebo-controlled trial, we evaluated the efficacy of oral tecovirimat in adults with laboratory-confirmed clade II mpox. Participants were randomly assigned in a 2:1 ratio to receive tecovirimat or placebo for 14 days. The primary outcome was clinical resolution, assessed in a time-to-event analysis in participants with active skin or mucosal lesions. Secondary outcomes included reduction in pain, assessed in all participants with laboratory-confirmed mpox and in those with severe pain at baseline (pain score, 7 to 10; scale, 0 [no pain] to 10 [worst pain imaginable]); complete lesion healing (assessed in a time-to-event analysis); viral DNA clearance; and safety.

Results

Of 412 participants who underwent randomization (275 to tecovirimat and 137 to placebo), 344 had laboratory-confirmed mpox, and 336 had active skin or mucosal lesions and were included in the primary analysis. By day 29, the estimated cumulative incidence of clinical resolution was 83% with tecovirimat and 84% with placebo; the competing-risks hazard ratio for clinical resolution was 0.98 (95% confidence interval [CI], 0.74 to 1.31; P=0.89). No substantial between-group differences were seen in pain reduction among participants with severe pain (difference, 0.1 point; 95% CI, −0.8 to 1.0), in complete lesion healing (competing-risks hazard ratio, 0.97; 95% CI, 0.75 to 1.26), or in viral DNA clearance. The incidence of adverse events of grade 3 or higher was similar in the two groups (4% with tecovirimat and 3% with placebo).

Conclusions

This trial showed no evidence that tecovirimat therapy shortened the time to clinical resolution, reduced pain, or increased viral clearance among adults with clade II mpox. (Funded by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health; STOMP/A5418 ClinicalTrials.gov number, NCT05534984.)

Source: 

Link: https://www.nejm.org/doi/full/10.1056/NEJMoa2506495?af=R&rss=currentIssue

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#Report on #influenza viruses received and tested by the #Melbourne #WHO CC for #Reference and Research on #Influenza during 2024

 

Abstract

As part of its role in the World Health Organization (WHO) Global Influenza Surveillance and Response System (GISRS), the WHO Collaborating Centre for Reference and Research on Influenza in Melbourne received 12,180 human influenza-positive samples during 2024. Viruses were analysed for their antigenic, genetic, and antiviral susceptibility properties. Selected viruses were propagated in qualified cells or embryonated hens’ eggs for potential use in seasonal influenza virus vaccines. During 2024, influenza A(H1N1)pdm09 and A(H3N2) viruses predominated, accounting for 33% and 42%, respectively, of all viruses received, compared to 5% for influenza B/Victoria. Of note, one influenza A(H5N1) virus was also received in 2024. The majority of A(H1N1)pdm09 (98%), A(H3N2) (88%) and influenza B (100%) viruses analysed at the Centre were found to be antigenically and genetically similar to the respective WHO recommended vaccine strains for the Southern Hemisphere in 2024. Of 4,007 samples tested for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir, twelve A(H1N1)pdm09 viruses and one B/Victoria virus showed highly reduced inhibition against oseltamivir or zanamivir. Of 3,294 total samples sequenced for baloxavir susceptibility, 18 of the 1,825 A(H3N2) samples were identified with genetic evidence of reduced susceptibility to baloxavir marboxil in the PA gene.

Source: 

Link: https://ojs.cdi.cdc.gov.au/index.php/cdi/article/view/3449

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#SARS-CoV-2 Error Catastrophe Under #Molnupiravir: #Mutagenic Enhancement Enables Viral #Persistence with Impaired Fitness

 

Abstract

Molnupiravir induces mutations that render severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication-competent through error catastrophe mechanisms. Previous studies showed no resistant virus emergence during prolonged molnupiravir treatment, with no resistant variants reported. However, these approaches were limited by genetic uniformity at passage initiation. To investigate viral population dynamics under enhanced genetic diversity, we employed mutagenic pre-treatment using 5-fluorouracil (5-FU) and favipiravir to generate diverse quasi-species populations before molnupiravir selection pressure. Viral populations were treated with stepwise increasing molnupiravir concentrations (10 μM ⟶ 25 μM ⟶ 40 μM) over ten serial passages. Viral detectability, plaque morphology, and mutation accumulation were analyzed using molecular and sequencing approaches. Only high-concentration favipiravir (1000 μM) pre-treatment maintained detectable viral RNA through ten passages under 40 μM molnupiravir, while favipiravir (500 μM) and 5-FU groups became undetectable after passage 6. Surviving populations formed extremely small plaques with markedly reduced replication capacity. Next-generation sequencing revealed extensive mutation accumulation across viral proteins, including polymerase proteins. Individual viable virus isolation was unsuccessful, and large-scale propagation could not be achieved. These findings demonstrate apparent survival rather than true resistance to molnupiravir, characterized by severely compromised viral fitness.

Source: 

Link: https://www.mdpi.com/1999-4915/18/2/273

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#Baloxavir outperforms #oseltamivir, #favipiravir, and #amantadine in treating lethal #influenza #H5N1 HA clade 2.3.4.4b #infection in #mice

 

Abstract

Intercontinental spread of highly pathogenic avian influenza A(H5N1) viruses poses significant pandemic risks and necessitates strong protective countermeasures. We evaluated the therapeutic efficacy of the neuraminidase inhibitor oseltamivir, the polymerase inhibitors baloxavir and favipiravir, and an ion-channel blocker amantadine, against severe influenza A(H5N1) virus infection in female BALB/c mice. Baloxavir (≥10 mg/kg, 1 dose) fully protected mice from death, significantly reduced virus respiratory replication, and prevented neuroinvasion. Oseltamivir (≥100 mg/kg/day for 5 days) provided limited survival benefits, reduced lung titers but failed to prevent viral neuroinvasion. Favipiravir (≥100 mg/kg/day for 5 days) provided partial protection, although did not reduce viral titers in lungs and brain. Amantadine provided no benefits. Although all drugs inhibited A(H5N1) viruses in vitro, in vivo correlations did not extend beyond baloxavir. Our results indicate that baloxavir is the most reliable treatment to address both respiratory replication and systemic spread of contemporary A(H5N1) viruses in mice and should be considered in pandemic planning.

Source: 

Link: https://www.nature.com/articles/s41467-026-69721-5

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#Prognostic factors in #H7N9 avian #influenza: a systematic review based on case reports

 

Abstract

Objective

The H7N9 avian influenza virus, identified in China in 2013, has posed a significant threat to public health due to its high mortality rate. This systematic review aims to evaluate the clinical characteristics and mortality risk factors of H7N9 patients.

Methods

English and Chinese databases (PubMed, Web of Science, Embase, CNKI, VIP, Wanfang) were searched for studies on laboratory-confirmed H7N9 cases with available data on symptom onset, diagnosis time, clinical features, oseltamivir administration, and outcomes. Univariate and multivariate analyses were performed on the pooled case data to assess the relationship between clinical factors and mortality risk.

Results

A total of 166 studies including 237 H7N9 cases were analyzed, with an overall mortality rate of 41.77%. Univariate analysis showed higher mortality in patients with advanced age ≥ 66 years (62.50%), those with underlying diseases (60.20%), those who received oseltamivir ≥ 8 days after symptom onset (54.17%), and those diagnosed ≥ 11 days after onset (62.75%), whereas patients treated with oseltamivir within 2 days of onset had the lowest mortality (17.39%). Multivariate analysis identified advanced age ≥ 66 years (OR = 3.10, 95% CI: 1.07–8.99, P = 0.037) and delayed oseltamivir administration after symptom onset (OR = 4.63, 95% CI: 1.12–19.18, P = 0.034) as independent predictors of mortality, while sex, underlying diseases, and onset-to-diagnosis time were not statistically significant.

Conclusion

Older age and delayed initiation of oseltamivir are key independent predictors of mortality in H7N9 infection. Prompt diagnosis is crucial to facilitate early antiviral treatment, which may improve survival. Future prospective studies are needed to validate these findings and optimize clinical management.

Clinical trial registration

Not applicable.

Source: 

Link: https://link.springer.com/article/10.1186/s12879-026-12908-4

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Impaired #host shutoff is a fitness cost associated with #baloxavir marboxil #resistance #mutations in #influenza A virus PA/PA-X nuclease domain

 

Abstract

The polymerase acidic (PA) protein is a subunit of the trimeric influenza A virus (IAV) RNA-dependent RNA polymerase and the target of the anti-influenza drug baloxavir marboxil (BXM). As with other direct-acting antivirals, treatment with BXM can lead to selection of viruses carrying resistance mutations. If these mutations have negligible fitness costs, resistant viruses can spread widely and render existing treatments obsolete. Multiple BXM resistance mutations in the nuclease domain of PA have been identified, with I38T and I38M amino acid substitutions occurring frequently. These mutations have minimal to no effects on viral polymerase activity, virus replication, or transmission. However, for reasons that are not well understood, viruses with BXM resistance substitutions have not been able to compete with parental wild-type strains. The IAV genome segment encoding PA also encodes the host shutoff nuclease PA-X, which shares the endonuclease domain with PA but has a unique C-terminal domain generated by ribosomal frameshifting during translation. Unlike their effects on PA activity, the effects of BXM or the I38T/M substitutions on PA-X function remain uncharacterized. In our work, for the first time, we directly examine the effects of baloxavir and the I38T/M substitutions on PA-X activity and show that baloxavir inhibits PA-X activity in a dose dependent manner. Most importantly, we also demonstrate that the I38T/M mutations significantly impair the host shutoff activity of PA-X proteins from different IAV strains of H1N1, H3N2, and H5N1 subtypes. Our work reveals that the deleterious effects of I38T/M on PA-X function may represent an important barrier to the spread of BXM-resistant viruses.

Source: 

Link: https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1013550

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Genomic #Evolution of #Influenza A Virus During the 2024-2025 Season, the Johns Hopkins Health System: Antigenic Drift Reduces Serum Neutralization

 

Abstract

Introduction

Seasonal influenza causes significant global morbidity, mortality, and economic burden. Ongoing viral evolution can lead to vaccine mismatch and the emergence of antiviral resistance, highlighting the importance of genomic surveillance. The 2024–2025 influenza season was characterized by high incidence and increased hospitalizations.

Methods

We analyzed influenza A virus (IAV) genomes and clinical characteristics from the 2024–2025 season. Whole-genome sequencing was performed on 648 influenza A–positive clinical specimens collected between October 2024 and April 2025.

Results

Hemagglutinin (HA) sequences were recovered from 74.23% (481/648) of samples and used for subtyping and phylogenetic analysis. A(H1N1)pdm09 and A(H3N2) viruses co-circulated, representing 55.5% and 44.5% of cases, respectively. Among A(H1N1)pdm09 viruses, the HA1 substitution T120A, located near the Sa antigenic site, increased more than twofold compared with the prior season. Circulating A(H3N2) viruses belonged to multiple HA subclades and exhibited distinct amino acid substitutions at key antigenic sites. Neutralization assays using sera from individuals vaccinated with the 2024–2025 seasonal influenza vaccine demonstrated reduced neutralization of three dominant A(H1N1)pdm09 isolates and two A(H3N2) isolates compared with vaccine strains, consistent with antigenic drift. In addition, the neuraminidase substitution S247N, previously associated with reduced oseltamivir susceptibility, was detected in 13.9% of A(H1N1)pdm09 samples.

Discussion

These findings demonstrate ongoing antigenic drift and the presence of antiviral resistance–associated mutations during the 2024–2025 influenza season, underscoring the need for continued genomic surveillance to guide vaccine and antiviral strategies.

Source: 

Link: https://academic.oup.com/jid/advance-article/doi/10.1093/infdis/jiag069/8461561#google_vignette

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Post-exposure #prophylaxis with #favipiravir among #household close contacts to confirmed #COVID19 cases: A cluster-randomized trial (PEPfavi)

 

Abstract

Background

Household transmission of SARS-CoV-2 remains a key driver of community spread, with secondary attack rates in Thai households reaching approximately 50 %. There is limited evidence supporting the efficacy of antiviral post-exposure prophylaxis (PEP) in this context.

Methods

The phase 2/3, open-label, (1:1) cluster-randomized controlled trial in Thailand, 168 household close contacts from 76 index cases were enrolled to receive either favipiravir-PEP (FPV-PEP) (1600–2000 mg/day for 7 days) or usual care. The efficacy of FPV-PEP was investigated in preventing SARS-CoV-2 infection after contact with index cases.

Results

The incidence of confirmed SARS-CoV-2 infection was lower in the FPV-PEP group than in the usual care group (7.32 % vs. 14.47 %), although the difference was not statistically significant. A trend toward fewer early positive rapid diagnostic test results on day 3 was observed in the FPV-PEP group. Symptom development was less frequent among FPV-PEP recipients, with fewer cases of fever, rhinorrhea, and myalgia. A significantly higher probability of remaining asymptomatic and delayed symptom onset was observed in the FPV-PEP group. No participants developed severe COVID-19 or required hospitalization.

Conclusion

FPV-PEP was associated with a lower incidence of fever, rhinorrhea, and myalgia among household contacts. While a reduction in secondary transmission was observed, it did not reach statistical significance. Further large-scale studies are warranted to clarify its role in preventing household transmission.

Source: 

Link: https://www.sciencedirect.com/science/article/pii/S1876034126000225?via%3Dihub

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#Oseltamivir and #baloxavir monotherapy and combination #therapy efficacy against clade 2.3.4.4b #H5N1 #influenza virus infection in #ferrets

 

Abstract

Neuraminidase inhibitors (NAIs) and cap-dependent endonuclease inhibitors (CENIs) represent two classes of antiviral drugs recommended for early treatment of patients with seasonal influenza A virus (IAV) infections. However, only limited human data, particularly on combination antiviral treatment, are available to inform optimal dosing regimens against novel IAVs, including highly pathogenic avian influenza A(H5N1) virus, associated with severe disease. Clade 2.3.4.4b A(H5N1) viruses have caused outbreaks in avian and mammalian species worldwide, highlighting the need to assess antiviral drug efficacy against these strains. We challenged ferrets with a D1.1 genotype A(H5N1) virus and treated infected animals with the NAI oseltamivir phosphate (OST) and the CENI baloxavir acid (BXA), alone or in combination, with treatment onset commencing pre- or post-symptom onset (24- or 48-hours post-inoculation (p.i.), respectively). When administered pre- or post-illness onset, BXA, but not OST, monotherapy provided significant reduction of clinical signs and significantly decreased infectious viral levels (in both respiratory and extrapulmonary specimens) compared with mock-treated animals. Combination OST/BXA treatment, when administered pre- or post-symptom onset, resulted in significant improvements in both metrics versus OST monotherapy. These data support continued investigation of antiviral treatment modalities that include both NAI and CENI for patients with mild and severe A(H5N1) disease.

Source: 

Link: https://www.nature.com/articles/s42003-026-09607-w

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#Management of #critical illness in an #adolescent caused by highly pathogenic avian #influenza #H5N1 virus infection in #BC, #Canada

 

Summary

Highly pathogenic avian influenza A(H5N1) viruses have been circulating among wild birds and are enzootic in poultry in some areas of the world with spillover to a wide range of terrestrial and marine mammals. Since 1997, sporadic animal to human, primarily poultry to human, transmission of highly pathogenic avian influenza A(H5N1) viruses has been reported in 25 countries. More recently there have been locally acquired infections in the Americas due to the 2.3.4.4b clade of the virus. Most of the recently detected human infections in the USA have been relatively mild but there have been cases of critical illness reported in several countries. In this Grand Round we present the first locally acquired highly pathogenic avian influenza A(H5N1) virus infection in Canada, which was in a 13-year-old female, who developed severe disease requiring prolonged critical care. She was infected with a clade 2.3.4.4b, genotype D1.1 virus and developed evidence of cytokine storm and received several modalities of care including combination antiviral therapy, renal replacement therapy, therapeutic plasma exchange, and invasive mechanical ventilation support with veno-venous extracorporeal life support. She recovered and was discharged home without requirement for additional support. This Grand Round describes important clinical and management considerations for critically ill patients infected with highly pathogenic avian influenza A(H5N1) virus.

Source: Lancet Infectious Diseases, https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(25)00773-X/abstract?rss=yes

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Comprehensive evaluation of #therapeutic #effectiveness and #safety profiles of #baloxavir marboxil for managing #influenza virus infection in #pediatric populations: a systematic #review with pooled meta-analytic data

 

Abstract

Objective: 

This systematic review aimed to assess the clinical effectiveness and safety profile of baloxavir marboxil for managing influenza in pediatric populations.

Methods: 

This review has been registered on the INPLASY platform (INPLASY2025110063). Designed in accordance with the PRISMA 2020 guidelines, we searched four major biomedical databases (PubMed, Embase, Web of Science, Cochrane Library) covering publications from January 1, 2015, to January 30, 2025. Eligibility criteria encompassed both randomized controlled trials and observational cohort studies evaluating this antiviral agent in children with laboratory-confirmed influenza. Methodological rigor was appraised using the Cochrane Collaboration's risk of bias instrument for randomized controlled trials (RCTs) and the Newcastle-Ottawa Quality Assessment Scale for cohort studies. Statistical synthesis was conducted using RevMan 5.3 software (Version 5.3.5) with metafor package implementation.

Results: 

Our analysis incorporated 12 clinical investigations involving a total of 4,586 patients. A random-effects model meta-analysis demonstrated that, compared to neuraminidase inhibitors (oseltamivir, zanamivir, peramivir, laninamivir), baloxavir marboxil achieved accelerated resolution of febrile symptoms (MD = −13.16 h, 95% CI: −19.16 to −7.15, P < 0.0001). Subgroup analyses stratified by viral subtype demonstrated consistent therapeutic advantages in influenza A infections (random-effects model, MD = −9.40 h, 95% CI: −18.31 to −0.49, P = 0.04), particularly regarding time to symptom alleviation (fixed-effect model, MD = −8.50 hours, 95% CI: −13.14 to −3.86, P = 0.0003). Safety assessments indicated a 59% reduction in drug-related adverse events relative to oseltamivir (fixed-effect model, OR 0.41, 95% CI 0.31–0.56; P < 0.001), while total adverse event rates showed comparable incidence between treatment arms (fixed-effect model, OR = 0.85, 95% CI: 0.69–1.05, P = 0.14).

Conclusion: 

These findings suggest baloxavir marboxil demonstrates faster fever resolution and a favorable safety profile in pediatric influenza management. However, continuous monitoring for baloxavir-resistant mutations (such as PA/I38T) in the pediatric population is warranted. Furthermore, confirmation through large-scale multicenter trials with extended follow-up periods remains warranted.

Source: Frontiers in Pediatrics, https://www.frontiersin.org/journals/pediatrics/articles/10.3389/fped.2025.1733111/full

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#Clinical Features and #Management of a Critical #Human Case of #H10N3 Avian #Influenza: A Case Report and Literature Review

 

Highlights

• Nonspecific early signs hinder prompt diagnosis of H10N3 infection.

• H10N3 human infection remains rare but with high clinical severity.

• All patients had bird exposure and developed fever, cough, and dyspnoea.

• Diagnosis was confirmed by sequencing; imaging revealed viral pneumonia.

Abstract

Background

Since the first human case of H10N3 Avian Influenza in Jiangsu, China (April 2021), three cases have been reported globally. However, clinical and treatment data remain limited. Therefore, we describe the fourth patient’s epidemiology, clinical manifestations, diagnostics, treatment.

Case presentation

A 23-year-old woman, previously well, presented on 12 Dec 2024 with fever, dry cough and breathlessness after pig and chicken contact. CT showed bilateral pneumonia. Despite high-flow oxygen and broad-spectrum antibiotics she deteriorated, requiring intubation, lung-protective ventilation and VV-ECMO. Bronchoalveolar lavage isolated H10N3 influenza virus. Treatment with oseltamivir and baloxavir plus prone-position ventilation led to clinical improvement.

Conclusion

Due to its nonspecific early symptoms, H10N3 is difficult to diagnose promptly, increasing the risk. Early recognition, antiviral therapy, and aggressive support are essential in managing severe infections.

Source: 

Link: https://www.ijidonline.com/article/S1201-9712(26)00002-0/fulltext

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#Remdesivir as a potent #antiviral against prototype and current #epidemic #Oropouche virus #strains (BeAn19991 and PE-IAM4637)

 

Highlights

• We generated a recombinant reporter OROV that expresses the eGFP fluorescent protein in infected cells.

• We found that remdesivir efficiently inhibited the replication of Oropouche virus (OROV) using this reporter OROV.

• We demonstrated strain-dependent differences in the replication efficiency of OROV.

Abstract

The Oropouche virus (OROV), an orthobunyavirus transmitted by biting midges, is the causative agent of Oropouche fever, which has caused multiple outbreaks in South and Central America. During the most recent epidemic in 2023–2025, more than 25,000 laboratory-confirmed cases were reported in Brazil, and no licensed antivirals have been reported to be effective date. In this study, we generated a recombinant OROV-expressing enhanced green fluorescent protein (rOROV/GFP) to facilitate rapid and sensitive antiviral evaluation. Growth kinetics demonstrated that rOROV/GFP replicated less efficiently than wild-type rOROV and that the historical prototype strain (BeAn19991) exhibited higher replication efficiency than the recent epidemic isolate (PE-IAM4637) in both Vero E6 and Huh7 cells. Using this system, we evaluated the antiviral activity of ribavirin, favipiravir (T-705), and remdesivir against OROV. All three compounds inhibited OROV replication in a dose-dependent manner, with remdesivir showing the greatest potency (IC₅₀ values of 0.31 µM). Taken together, our findings highlight remdesivir as a promising candidate for the treatment of Oropouche fever caused by OROV. Furthermore, we established rOROV/GFP as a powerful tool for antiviral drug screening.

Source: 

Link: https://www.sciencedirect.com/science/article/pii/S0168170225001583?via%3Dihub

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#Influenza PA #Substitutions and Genetic Diversity of #H1N1pdm09, #H3N2, and B/Victoria Viruses in #Japan During the 2023–2024 Season

 

Abstract

We characterized influenza A(H1N1)pdm09, A(H3N2), and B/Victoria viruses circulating in Japan during 2023–2024, focusing on lineage placement relative to WHO-recommended vaccine strains and on baloxavir resistance (PA/I38T substitutions). We enrolled 210 outpatients with influenza-like illness across eight clinics in six prefectures (October 2023–September 2024). Of these, 209 had an analyzable pre-treatment respiratory specimen for RT-PCR; hemagglutinin (HA) and neuraminidase (NA) genes were sequenced by next-generation sequencing (NGS). PA/I38T substitutions that confer baloxavir resistance were assessed by cycling-probe RT-PCR, Sanger sequencing, and NGS. HA phylogenies were constructed with global datasets and WHO vaccine reference strains. Of 209 pre-treatment specimens, 181 were influenza-positive (A(H1N1)pdm09 44.2%, A(H3N2) 37.6%, B/Victoria 18.2%); 51 follow-up specimens were collected ≈4–5 days after baloxavir or neuraminidase inhibitor therapy. HA phylogeny placed A(H1N1)pdm09 in clades 5a.2a/5a.2a.1 with predominance of subclade D.2. A(H3N2) clustered exclusively in clade 2a.3a.1 (J lineage, mostly J.1), indicating a mismatch with the season’s A/Darwin/9/2021 vaccine component and supporting the subsequent J-lineage update. All B/Victoria genomes fell within V1A.3a.2 on a C.5 backbone (C.5.1 and C.5.7). No PA/I38T variant was detected in any pre-treatment specimen. Post-baloxavir, PA/I38T emerged in one A(H3N2) case (confirmed by all three methods) and in one B/Victoria case detected by NGS only (minority variant in a low-load sample). NA genes showed no substitutions associated with reduced susceptibility to laninamivir (e.g., E119A, G147E). During 2023–2024, A(H1N1)pdm09 and B/Victoria remained genetically aligned with their vaccine components, whereas A(H3N2) shifted to the J lineage, consistent with the 2024–2025 vaccine update. Although pre-treatment PA/I38T was absent, low-frequency on-therapy selection was observed, including a rare PA/I38T in influenza B/Victoria detected by NGS, suggesting the value of deep sequencing when viral loads are low. These integrated genomic–clinical data support vaccine strain realignment for H3N2 and continued monitoring of baloxavir resistance in outpatient care.

Source: 

Link: https://www.mdpi.com/1999-4915/18/1/13

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