#Niclosamide Inhibits the #Replication of Highly Pathogenic Avian #Influenza #H5Nx Viruses and Antiviral-Resistant #Mutants

 

Highlights

• Niclosamide blocks the replication of highly pathogenic avian influenza H5 viruses

• Niclosamide is effective against H5 viruses with antiviral-resistant substitutions

• Niclosamide has potential as host-targeting anti-influenza drug

Abstract

The recurrent spillover of highly pathogenic avian influenza (HPAI) H5 viruses into humans represents a major public health concern that is exacerbated by the emergence of drug-resistant viral variants. Host-targeting antiviral approaches, including drug repurposing, offer a promising alternative to conventional virus-directed therapeutics. Here, we evaluated the antiviral activity of niclosamide, an FDA-approved anthelmintic drug, against four HPAI A(H5Nx) viruses, two A(H5N1), one A(H5N6), and one A(H5N8), recently isolated from human cases. Niclosamide inhibited all four viruses in plaque reduction assays with MDCK cells, with low inhibitory concentration 50% (IC50) values (0.68–1.40 μM) and minimal cytotoxicity at effective concentrations. These values were more potent than the IC50 values observed for the RdRp inhibitor favipiravir. Niclosamide treatment plus either baloxavir marboxil or favipiravir resulted in additive or near-additive interactions, as indicated by synergy scores of ±10. Importantly, niclosamide retained antiviral activity against HPAI A(H5Nx) viruses bearing resistance-associated amino acid substitutions (i.e., PA-I38T, baloxavir resistance and PB1-K229R, favipiravir resistance), consistent with its host-directed mechanism of action. Although there are barriers to be overcome such as a narrow therapeutic window, largely attributable to its poor bioavailability and some cytotoxicity, our findings suggest niclosamide has potential as a host-targeting therapeutic option against emerging zoonotic influenza viruses, particularly in settings involving antiviral-resistant escape mutants.

Source: 

Link: https://www.sciencedirect.com/science/article/pii/S016635422600080X?via%3Dihub

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#Antiviral treatment for #influenza

 

Abstract

Seasonal influenza is a widespread acute respiratory infection that causes significant illness and death worldwide. Two major antiviral classes are neuraminidase inhibitors (NAIs) and polymerase inhibitors. NAIs, including oseltamivir, zanamivir, peramivir and laninamivir, block viral release, while polymerase inhibitors such as baloxavir disrupt viral RNA replication. Early administration within 48 h of symptom onset reduces illness duration, severity and complications, particularly in high-risk groups. Oseltamivir is the most widely studied NAI, demonstrating reduced viral shedding, faster symptom resolution and lower complication rates, though gastrointestinal side effects are common. Higher doses generally do not improve outcomes compared to standard dosing. Zanamivir is more effective against influenza B and is inhibitory for most influenza A viruses resistant to oseltamivir, but the inhaled formulation is less suitable for patients with severe illness or airway disease. Intravenous (IV) zanamivir is approved for hospitalized influenza patients in some countries. Peramivir offers IV treatment options, while laninamivir is mainly used in Japan. Baloxavir shows superior viral load reduction and comparable symptom relief to oseltamivir in outpatients, though resistance variants can emerge. Favipiravir and newer polymerase inhibitors are under investigation. Combination therapies may enhance recovery, with limited evidence. Overall, timely antiviral use is critical to reducing influenza’s burden.

This article is part of the Theo Murphy meeting issue ‘Evaluating anti-infective drugs’.

Source: 

Link: https://royalsocietypublishing.org/rstb/article/381/1949/20240344/481548/Antiviral-treatment-for-influenza

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Antiviral activities of multiple #antivirals against highly pathogenic avian #influenza A #H5N1 in vitro and in mice

 

ABSTRACT

In 2024, a bovine H5N1 strain was first isolated from dairy cows in Texas and confirmed to transmit cross-species to humans. Therefore, research on treatments for human infection should be accelerated. In our study, the antiviral effects of baloxavir acid (BXA), oseltamivir carboxylate (OSC), EIDD-1931 (NHC), and ribavirin (RBV) against five H5N1 strains were evaluated in vitro. Cell viability and viral replication were measured to assess the antiviral effects. The results showed that the EC50 of BXA treatment was the lowest. The BXA/NHC and BXA/OSC combination treatments showed more potent inhibitory effects than each monotherapy. The 15 mg/kg baloxavir marboxil (BXM) / 125 mg/kg molnupiravir (MNP) and the 15 mg/kg BXM / 10 mg/kg oseltamivir phosphate (OSP) were tested in BALB/c mice. The mice were inoculated with 10 times the 50% mouse lethal dose (10 MLD50) of bovine H5N1 virus. Treatments began 1-day post-infection (1 dpi) and were administered orally twice daily for 5 or 7 days. Changes in body weight, clinical signs, and survival were monitored; lung and brain tissues were collected for virological, immunological, and histological analyses. Most mice died from severe neurological symptoms. Compared with the 5-day treatment, the 7-day treatment effectively inhibited viral replication and increased survival rates to 50% in BXM, BXM/MNP, and BXM/OSP treatments. Mice treated with BXM/MNP or BXM/OSP combination therapy showed lower viral yields in the lungs than those treated with BXM alone. The results provide a reference for human treatment, and extending the 7-day combination treatment should be considered.

Source: Emerging Microbes and Infections, https://www.tandfonline.com/journals/temi20

Link: https://www.tandfonline.com/doi/full/10.1080/22221751.2026.2645843

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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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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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#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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#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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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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#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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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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#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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Evaluation of #therapeutic effect of #baloxavir marboxil against high pathogenicity avian #influenza virus infection in #duck model

 

Abstract

Since 2020, high pathogenicity avian influenza virus (HPAIV) infections in wild birds have been frequently reported. Because HPAIV infection has occasionally caused outbreaks in captive rare birds, application of antiviral drugs for treatment purposes against them has been considered from the perspective of conservation medicine. In this study, the therapeutic efficacy of baloxavir marboxil (BXM) was evaluated using a duck model to help establish the post-infection treatment for rare birds. Sixteen four-week-old ducks were divided into four groups and intranasally inoculated with the HPAIV strain A/crow/Hokkaido/0103B065/2022 (H5N1). BXM was orally administered once daily at doses of 12.5, 2.5, 0.5, and 0 mg/kg to each of the four groups from 2 to 6 days post-infection. Blood samples were collected at 2, 8, and 24 hours after the initial BXM administration to measure the plasma concentrations of its active form, baloxavir acid (BXA). All ducks were monitored until 14 days post-infection, and their oral and cloacal swabs were collected for virus recovery. All eight ducks administered with 12.5 or 2.5 mg/kg of BXM survived, demonstrating a significant reduction in virus recovery compared to the 0 mg/kg group. Pharmacokinetic/pharmacodynamic (PK/PD) analysis of BXA suggested that parameters such as Cmax and AUC0–24hr were correlated with the suppression of virus shedding. These findings demonstrated that BXM administration within 48 hours post-HPAIV infection in ducks effectively reduced mortality and virus shedding. The comparison of PK parameters may help estimate efficient BXM dosing strategies in rare birds.

Competing Interest Statement

This study was supported by a collaborative research project between Hokkaido University and Shionogi & Co., Ltd. M.S., R.D.O, H.O., and T.S. are employees of Shionogi & Co., Ltd. M.M. is a former employee of Shionogi & Co., Ltd. These affiliations did not influence the study design, data collection, analysis, or interpretation. The remaining authors declare no competing interests.

Funder Information Declared

Environmental Restoration and Conservation Agency, JPMEERF20254004

Japan Science and Technology Agency, JPMJSP2119

Japan Agency for Medical Research and Development, https://ror.org/004rtk039, JP223fa627005, JP24wm000125008

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.10.24.684283v1

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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) RNAdependent 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.

Competing Interest Statement

The authors have declared no competing interest.

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.09.22.677688v1

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A case of #H10N3 avian #influenza in a young woman

 

Context and significance

The avian influenza A virus subtype H10N3 is a possible candidate for causing a fatal flu and may present a serious public health threat. Research increasingly shows that the avian influenza virus H10N3 can be transmitted from birds to humans, causing severe viral pneumonia and potentially leading to acute respiratory distress syndrome and respiratory failure. Researchers at the Fourth People’s Hospital of Nanning (China) provide evidence supporting the cross-species transmission of the avian influenza virus H10N3 to humans, which can give rise to severe pneumonia. The authors report that a female patient with avian influenza virus H10N3 infection, who was suffering from severe pneumonia, respiratory failure, pneumothorax, and numbness and dysesthesia in her feet, recovered after receiving appropriate therapy and was discharged from the hospital.

Highlights

• A young woman contracted the avian influenza virus H10N3

• Secondary infections, pneumothorax, and foot numbness developed consecutively

• Baloxavir marboxil and oseltamivir were administered

Summary

Background

Avian influenza viruses, frequently identified in wild waterfowl and poultry, have occasionally been transmitted to humans, causing severe respiratory diseases. This report covers the fourth case of a human contracting the H10N3 subtype of avian influenza virus.

Methods

A case of novel avian influenza virus subtype H10N3 was detected in a female patient hospitalized in Nanning, China, in December 2024. Blood, feces, urine, and bronchoalveolar lavage fluid were collected from the patient for medical analysis during the hospitalization.

Findings

A case of novel avian influenza virus subtype H10N3 was detected in a female patient hospitalized in Nanning, China, in December 2024. She also had a history of exposure to live poultry. This case represents the fourth documented instance of H10N3 infection in humans. She was treated with a combination of baloxavir marboxil and oseltamivir. She exhibited extensive lung lesions. Additionally, she presented complicating factors, including secondary infection, pneumothorax, and numbness in her feet. She recovered and was discharged on March 27, 2025, amid comprehensive supportive care, which included therapy with baloxavir marboxil, oseltamivir, fluconazole, tigecycline, amikacin, extracorporeal membrane oxygenation, and rehabilitation therapy.

Conclusions

The virus was effectively cleared by the combination therapies. The internal genes of the H10N3 virus in this patient were highly homologous to the corresponding genes from the A/Yunnan/2024 virus (GenBank accession numbers, hemagglutinin [HA] [GenBank: PP555669] and PB-2 [GenBank: PP555666]).

Funding

This work was funded by the Fourth People’s Hospital of Nanning - Human Immunodeficiency Virus/Acquired Immune Deficiency Syndrome (HIV/AIDS) Clinical Treatment Center of Guangxi (Nanning).

Source: Med., https://www.cell.com/med/abstract/S2666-6340(25)00272-7

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#Global #update on susceptibilities of #influenza viruses to #neuraminidase #inhibitors and the cap-dependent endonuclease inhibitor #baloxavir, 2020–2023

Highlights

• Antiviral susceptibility to NA inhibitors and PA inhibitor baloxavir was determined for seasonal and zoonotic influenza viruses circulating globally during 2020–2023.

• Low global frequencies (0.1-0.2%) of seasonal influenza viruses with reduced or highly reduced inhibition by NAI inhibitors were observed as in previous years.

• Low global frequencies of seasonal influenza viruses (∼ 0.1%) with reduced susceptibility to baloxavir were observed, with the rate in Japan elevated (3.3%) in 2022–2023, as has been seen previously.

• For zoonotic viruses, 2.7% contained genetic markers associated with reduced or highly reduced inhibition to NA inhibitors and none contained markers associated with reduced susceptibility for baloxavir.

• For the treatment of influenza, NA inhibitors and baloxavir remain suitable.

ABSTRACT

Antiviral susceptibility of influenza viruses is monitored by the World Health Organization Global Influenza Surveillance and Response System. This study describes a global analysis of the susceptibility of influenza viruses to neuraminidase (NA) inhibitors (NAIs, oseltamivir, zanamivir, peramivir, laninamivir) and the cap-dependent endonuclease inhibitor (CENI, baloxavir) for three periods (May to May for 2020–2021, 2021–2022 and 2022–2023). In particular, global influenza activity declined significantly in 2020-2021 and 2021-2022 when compared to the pre-pandemic period of COVID-19. Combined phenotypic and NA sequence-based analysis revealed that the global frequency of seasonal influenza viruses with reduced or highly reduced inhibition (RI/HRI) by NAIs remained low, 0.09% (2/2224), 0.12% (27/23465) and 0.23% (124/53917) for 2020–2021, 2021–2022 and 2022–2023, respectively. As in previous years, NA-H275Y in A(H1N1)pdm09 viruses was the most frequent substitution causing HRI by oseltamivir and peramivir. Sequence-based analysis of polymerase acidic (PA) protein supplemented with phenotypic testing revealed low global frequencies of seasonal influenza viruses with reduced susceptibility (RS) to baloxavir, 0.07% (1/1376), 0.05% (9/18380) and 0.12% (48/39945) for 2020–2021, 2021–2022 and 2022–2023, respectively; commonly associated substitutions were PA-I38T/M/L. In Japan, the rate was 3.3% (16/488) during 2022–2023, with 11 A(H3N2) viruses having PA-I38T/M substitutions. For zoonotic viruses, 2.7% (3/111) contained substitutions, one each NA-H275Y, NA-S247N and NA-N295S, associated with RI/HRI NAI phenotypes, and none contained PA substitutions associated with RS to baloxavir. In conclusion, the great majority of seasonal and zoonotic influenza viruses remained susceptible to NAIs and CENI baloxavir.

Source: Antiviral Research, https://www.sciencedirect.com/science/article/abs/pii/S0166354225001433?via%3Dihub

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Efficacy of #baloxavir marboxil against #bovine #H5N1 virus in mice

Abstract

Since the first detection of highly pathogenic avian influenza (HPAI) H5N1 (clade 2.3.4.4b) in U.S. dairy cattle in early 2024, the virus has spread rapidly, posing a major public health concern as the number of human cases continues to rise. Although human-to-human transmission has not been confirmed, experimental data suggest that the bovine H5N1 virus can transmit via respiratory droplets in ferrets, highlighting its pandemic potential. With no vaccines currently available, antiviral drugs remain the only treatment option. Here, we investigate the efficacy of the polymerase inhibitor baloxavir marboxil (BXM) against this virus in mice. We find that early treatment post-infection is effective, but delayed treatment significantly reduces BXM efficacy and increases the risk of BXM resistance, underscoring the importance of timely BXM administration for effective treatment.

Source: Nature Communications, https://www.nature.com/articles/s41467-025-60791-5

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#WHO #clinical practice #guidelines for #influenza: an #update

Abstract

Background

Every year, more than one billion people around the world are infected with influenza, an acute infection of the respiratory tract. Influenza spreads from person to person through air, contaminated hands or objects. Antiviral and immunomodulatory drugs are available for treatment of patients and prophylaxis of exposed persons. Reverse transcription polymerase chain reaction (RT-PCR), nucleic acid amplification tests (NAATs) and rapid tests are available for the diagnosis of influenza. 

Objective 

The aim of this World Health Organization (WHO) guideline is to provide recommendations for the diagnosis, drug treatment and prophylaxis of influenza.

Method

This updated guideline has been developed in accordance with standards for trustworthy guidelines. The recommendations are based on systematic reviews on safety and effectiveness. They take into account the magnitude of benefits and harms of treatments, the reliability of the evidence, and the needs of patients and healthcare professionals.

Results

For non-severe influenza, there is a conditional recommendation to use baloxavir if the risk of severe illness is high. Antivirals are not recommended if the risk is low. There is also a strong recommendation against the use of antibiotics if bacterial co-infection is unlikely. Oseltamivir is conditionally recommended for severe influenza. Not recommended are peramivir and zanamivir, as well as macrolide antibiotics (in the absence of co-infection), mTOR inhibitors and plasma therapy, and corticosteroids. Baloxavir and oseltamivir are conditionally recommended for prophylaxis in asymptomatic persons who have been exposed to seasonal influenza viruses and would be at very high risk of becoming hospitalised. For zoonotic influenza, laninamivir and zanamivir are also conditionally recommended in addition to baloxavir and oseltamivir, regardless of individual risk. For diagnosis, the use of NAAT or digital immunoassay (DIA) for suspected non-severe influenza and nucleic acid amplification test (NAAT) for suspected severe influenza is recommended.

Source: Gesundheitswesen, https://www.thieme-connect.de/products/ejournals/abstract/10.1055/a-2571-3357#info

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#Influenza #H1N1pdm09 Virus #Resistance to #Baloxavir, #Oseltamivir and Sialic Acid Mimetics in Single and Dual #therapies: Insights from Human Airway Epithelia and Murine Models

Highlights

• Reconstituted human airway epithelia (HAE) are more effective than cell lines or mouse models for generating and predicting resistance-conferring mutations.

• The resistance barrier of oseltamivir is superior to baloxavir or HA targeting compounds in HAE or mouse model.

• HA-targeting therapeutics quickly led to resistant HA mutations without compromising viral fitness.

• A baloxavir-resistant virus with PA mutations E23G and C241Y was isolated in HAE.

• Combined therapy using clinical antiviral compounsd and HA-targeting compounds did not prevent the emergence of HA mutations.

Abstract

Influenza viruses pose a significant threat due to annual epidemics and pandemic potential. Resistance to current antivirals underscores the need for new drugs and strategies to prevent its emergence. We previously developed two novel HA-targeting compounds (CD-6’SLN and CD-SA) with demonstrated efficacy against influenza A and B strains. Here, we compared their resistance barrier to that of FDA-approved oseltamivir (OS) and baloxavir marboxil (BXM). We established a resistance testing assay in human airway epithelia (HAE) and in mice. We also evaluated the impact of combination therapies on resistance emergence. In HAE, highly reduced inhibition (HRI) by CD-6’SLN and CD-SA occurred within 2 and 4 weeks respectively without fitness loss, while reduced inhibition (RI) by baloxavir acid (BXA) emerged within 4 weeks. No reduction of susceptibility to OS was observed in the same time frame. Of note, emergence of RI by CD-SA was not delayed in BXA/CD-SA co-treatment, and slightly reduced upon OS/CD-SA co-treatment. In mice, RI by CD-SA was observed after 8 passages in one of three mice treated with OS/CD-SA, but not in mice with single therapies. This study demonstrates that (1) HAE represents a relevant model to detect emergence of resistance and (2) HA-targeting compounds are prone to induce resistance followed by BXA and OS. Importantly, combination of clinically available antivirals and HA-targeting compounds did not prevent the emergence of variants with HA substitutions. Additional research is needed to develop anti-influenza antivirals with high resistance barrier and compounds should be tested in HAE before moving to animal experimentation.

Source: Antiviral Research, https://www.sciencedirect.com/science/article/abs/pii/S0166354225001007?via%3Dihub

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Efficacy of #Baloxavir #Treatment in Preventing #Transmission of #Influenza

Abstract

Background

Baloxavir marboxil (baloxavir) rapidly reduces influenza virus shedding, which suggests that it may reduce transmission. Studies of treatment with neuraminidase inhibitors have not shown sufficient evidence that they prevent transmission to contacts.

Methods

We conducted a multicountry, phase 3b trial to assess the efficacy of single-dose baloxavir treatment to reduce influenza transmission from index patients to household contacts. Influenza-positive index patients 5 to 64 years of age were randomly assigned in a 1:1 ratio to receive baloxavir or placebo within 48 hours after symptom onset. The primary end point was transmission of influenza virus from an index patient to a household contact by day 5. The first secondary end point was transmission of influenza virus by day 5 that resulted in symptoms.

Results

Overall, 1457 index patients and 2681 household contacts were enrolled across the 2019–2024 influenza seasons; 726 index patients were assigned to the baloxavir group, and 731 to the placebo group. By day 5, transmission of laboratory-confirmed influenza was significantly lower with baloxavir than with placebo (adjusted incidence, 9.5% vs. 13.4%; adjusted odds ratio, 0.68; 95.38% confidence interval [CI], 0.50 to 0.93; P=0.01), with an adjusted relative risk reduction of 29% (95.38% CI, 12 to 45). The adjusted incidence of transmission of influenza virus by day 5 that resulted in symptoms was 5.8% with baloxavir and 7.6% with placebo; however, the difference was not significant (adjusted odds ratio, 0.75; 95.38% CI, 0.50 to 1.12; P=0.16). Emergence of drug-resistant viruses during the follow-up period occurred in 7.2% (95% CI, 4.1 to 11.6) of the index patients in the baloxavir group; no resistant viruses were detected in household contacts. No new safety signals were identified.

Conclusions

Treatment with a single oral dose of baloxavir led to a lower incidence of transmission of influenza virus to close contacts than placebo. (Funded by F. Hoffmann–La Roche and others; CENTERSTONE ClinicalTrials.gov number, NCT03969212.)

Source: The New England Journal of Medicine, https://www.nejm.org/doi/full/10.1056/NEJMoa2413156?query=TOC

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