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This retrospective cohort study analyzed data from a Japanese health insurance database to assess the effectiveness of baloxavir (n = 4822) for preventing severe events compared with oseltamivir (n = 10,523) in patients with influenza B. The primary endpoint was hospitalization incidence (Days 2-14). The secondary endpoints included intravenous antibacterial drug use, pneumonia hospitalization, heart failure hospitalization, inhalational oxygen requirement, and use of other anti-influenza drugs. The hospitalization incidence was significantly lower with baloxavir (0.15% vs. 0.37%; risk ratio: 2.48, 95% confidence interval: 1.13-5.43). Pneumonia and additional anti-influenza therapy were also less frequent with baloxavir, thus supporting its use. Trial Registration: UMIN Clinical Trials Registry Study ID: UMIN000051382.

BACKGROUND: This study sought to evaluate the cost-effectiveness of baloxavir marboxil compared with oseltamivir or no antiviral treatment from a US payer perspective using data from a real-world US administrative claims study. Given baloxavir\'s ability to rapidly stop viral shedding, the potential health economic implications of a baloxavir-induced population-level reduction in viral transmission was also explored.
METHODS: A decision tree cost-effectiveness model was developed for seasonal influenza (2018-2020) using a lifetime time horizon with 3.0% discounting for costs and quality-adjusted life-years (QALYs). Patients aged ≥ 12 years could receive baloxavir, oseltamivir or no antiviral treatment. Patient characteristics, complications, and costs were derived from the Merative™ MarketScan® Research Databases including US commercial claims and Medicare and Medicaid Supplemental databases. A scenario analysis explored the impact of reduced viral transmission with baloxavir.
RESULTS: In the base case analysis, baloxavir was cost-effective within a willingness-to-pay threshold of US$100,000/QALY compared with oseltamivir [incremental cost-effectiveness ratio (ICER), $6813/QALY gained] or no antiviral treatment (ICER, $669/QALY gained). The net monetary benefit (NMB) of baloxavir was $1180 and $6208 compared with oseltamivir and no treatment, respectively. The NMB of baloxavir increased linearly with reductions in viral transmission, where a 5% transmission reduction yielded an NMB of $2592 versus oseltamivir and $7621 versus no treatment. Baloxavir became dominant (more effective and less costly, with ICERs < 0) starting with a 12.0% reduction in viral transmission versus oseltamivir and 6.0% versus no antiviral treatment.
CONCLUSIONS: Baloxavir was cost-effective compared with oseltamivir or no antiviral treatment. The potential of baloxavir to reduce viral transmission offers a substantial economic benefit from a US payer perspective.
Baloxavir is a prescription medicine that reduces the duration of flu symptoms and reduces the likelihood of complications from the flu, including serious complications that may require hospitalization. Baloxavir may reduce the spread of the flu to healthy people by reducing the amount and duration of virus shedding from infected people. We designed a model to estimate the cost benefits of using baloxavir versus another flu treatment, known as oseltamivir, or no flu treatment at all. Using baloxavir led to more cost savings than oseltamivir or no treatment for people in the US who have commercial health insurance. Baloxavir was even more cost-effective in the scenario where it reduced the number of flu cases (transmission benefit). This could ultimately have a meaningful benefit across a large health insurance population.

Baloxavir acid (BXA) is a pan-influenza antiviral that targets the cap-dependent endonuclease of the polymerase acidic (PA) protein required for viral mRNA synthesis. To gain a comprehensive understanding on the molecular changes associated with reduced susceptibility to BXA and their fitness profile, we performed a deep mutational scanning at the PA endonuclease domain of an A (H1N1)pdm09 virus. The recombinant virus libraries were serially passaged in vitro under increasing concentrations of BXA followed by next-generation sequencing to monitor PA amino acid substitutions with increased detection frequencies. Enriched PA amino acid changes were each introduced into a recombinant A (H1N1)pdm09 virus to validate their effect on BXA susceptibility and viral replication fitness in vitro. The I38 T/M substitutions known to confer reduced susceptibility to BXA were invariably detected from recombinant virus libraries within 5 serial passages. In addition, we identified a novel L106R substitution that emerged in the third passage and conferred greater than 10-fold reduced susceptibility to BXA. PA-L106 is highly conserved among seasonal influenza A and B viruses. Compared to the wild-type virus, the L106R substitution resulted in reduced polymerase activity and a minor reduction of the peak viral load, suggesting the amino acid change may result in moderate fitness loss. Our results support the use of deep mutational scanning as a practical tool to elucidate genotype-phenotype relationships, including mapping amino acid substitutions with reduced susceptibility to antivirals.

Avian influenza outbreaks, including ones caused by highly pathogenic A(H5N1) clade 2.3.4.4b viruses, have devastated animal populations and remain a threat to humans. Risk elements assessed for emerging influenza viruses include their susceptibility to approved antivirals. Here, we screened >20,000 neuraminidase (NA) or polymerase acidic (PA) protein sequences of potentially pandemic A(H5Nx), A(H7Nx), and A(H9N2) viruses that circulated globally in 2010-2023. The frequencies of NA or PA substitutions associated with reduced inhibition (RI) or highly reduced inhibition (HRI) by NA inhibitors (NAIs) (oseltamivir, zanamivir) or a cap-dependent endonuclease inhibitor (baloxavir) were low: 0.60% (137/22,713) and 0.62% (126/20,347), respectively. All tested subtypes were susceptible to NAIs and baloxavir at sub-nanomolar concentrations. A(H9N2) viruses were the most susceptible to oseltamivir, with IC50s 3- to 4-fold lower than for other subtypes (median IC50: 0.18 nM; n = 22). NA-I222M conferred RI of A(H5N1) viruses by oseltamivir (with a 26-fold IC50 increase), but NA-S246N did not reduce inhibition. PA-E23G, PA-K34R, PA-I38M/T, and the previously unreported PA-A36T caused RI by baloxavir in all subtypes tested. Avian A(H9N2) viruses endemic in Egyptian poultry predominantly acquired PA-I38V, which causes only a <3-fold decrease in the baloxavir EC50 and fails to meet the RI criteria. PA-E199A/D in A(H7Nx) and A(H9N2) viruses caused a 2- to 4-fold decrease in EC50 (close to the borderline for RI) and should be closely monitored. Our data indicate antiviral susceptibility is high among avian influenza A viruses with pandemic potential and present novel markers of resistance to existing antiviral interventions.

UNASSIGNED: Influenza affects individuals of all ages and poses a significant threat during pandemics, epidemics, and sporadic outbreaks. Neuraminidase inhibitors (NAIs) are currently the first choice in the treatment and prevention of influenza, but their use can be hindered by viral resistance.
UNASSIGNED: This review summarizes current NAIs pharmacological profiles, their current place in therapy, and the mechanisms of viral resistance and outlines possible new indications, ways of administration, and novel candidate NAIs compounds.
UNASSIGNED: NAIs represent a versatile group of compounds with diverse administration methods and pharmacokinetics. While the prevalence of influenza virus resistance to NAIs remains low, there is heightened vigilance due to the pandemic potential of influenza. Several novel NAIs and derivatives are currently under assessment at various stages of development for the treatment and prevention of influenza.

Since May 2023, a novel combination of neuraminidase mutations, I223V + S247N, has been detected in influenza A(H1N1)pdm09 viruses collected in countries spanning 5 continents, mostly in Europe (67/101). The viruses belong to 2 phylogenetically distinct groups and display ≈13-fold reduced inhibition by oseltamivir while retaining normal susceptibility to other antiviral drugs.

Crimean-Congo hemorrhagic fever virus (CCHFV) is a highly pathogenic bunyavirus with a fatality rate of up to 40%. Currently, there are no licensed antiviral drugs for the treatment of CCHF; thus, the World Health Organization (WHO) listed the disease as a priority. A unique viral transcription initiation mechanism called \"cap-snatching\" is shared by influenza viruses and bunyaviruses. Thus, we tested whether baloxavir (an FDA-approved anti-influenza drug that targets the \"cap-snatching\" mechanism) could inhibit CCHFV infection. In cell culture, baloxavir acid effectively inhibited CCHFV infection and targeted CCHFV RNA transcription/replication. However, it has weak oral bioavailability. Baloxavir marboxil (the oral prodrug of baloxavir) failed to protect mice against a lethal dose challenge of CCHFV. To solve this problem, baloxavir sodium was synthesized owing to its enhanced aqueous solubility and pharmacokinetic properties. It consistently and significantly improved survival rates and decreased tissue viral loads. This study identified baloxavir sodium as a novel scaffold structure and mechanism of anti-CCHF compound, providing a promising new strategy for clinical treatment of CCHF after further optimization.

BACKGROUND: The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has lasted for three years. Coinfection with seasonal influenza may occur resulting in more severe diseases. The interaction between these two viruses for infection and the effect of antiviral treatment remains unclear.
METHODS: A SARS-CoV-2 and influenza H1N1 coinfection model on Calu-3 cell line was established, upon which the simultaneous and sequential coinfection was evaluated by comparing the viral load. The efficacy of molnupiravir and baloxavir against individual virus and coinfection were also studied.
RESULTS: The replication of SARS-CoV-2 was significantly interfered when the influenza virus was infected simultaneously or in advance (p < 0.05). On the contrary, the replication of the influenza virus was not affected by the SARS-CoV-2. Molnupiravir monotherapy had significant inhibitory effect on SARS-CoV-2 when the concentration reached to 6.25 μM but did not show any significant anti-influenza activity. Baloxavir was effective against influenza within the dosage range and showed significant effect of anti-SARS-CoV-2 at 16 μM. In the treatment of coinfection, molnupiravir had significant effect for SARS-CoV-2 from 6.25 μM to 100 μM and inhibited H1N1 at 100 μM (p < 0.05). The tested dosage range of baloxavir can inhibit H1N1 significantly (p < 0.05), while at the highest concentration of baloxavir did not further inhibit SARS-CoV-2, and the replication of SARS-CoV-2 significantly increased in lower concentrations. Combination treatment can effectively inhibit influenza H1N1 and SARS-CoV-2 replication during coinfection. Compared with molnupiravir or baloxavir monotherapy, combination therapy was more effective in less dosage to inhibit the replication of both viruses.
CONCLUSIONS: In coinfection, the replication of SARS-CoV-2 would be interfered by influenza H1N1. Compared with molnupiravir or baloxavir monotherapy, treatment with a combination of molnupiravir and baloxavir should be considered for early treatment in patients with SARS-CoV-2 and influenza coinfection.

Antiviral susceptibility of influenza viruses was assessed using a high-content imaging-based neutralization test. Cap-dependent endonuclease inhibitors, baloxavir and AV5116, were superior to AV5115 against type A viruses, and AV5116 was most effective against PA mutants tested. However, these three inhibitors displayed comparable activity (EC50 8-22 nM) against type C viruses from six lineages. Banana lectin and a monoclonal antibody, YA3, targeting the hemagglutinin-esterase protein effectively neutralized some, but not all, type C viruses.