An orally active entry inhibitor of influenza A viruses protects mice and synergizes with oseltamivir and baloxavir marboxil.

Seasonal or pandemic illness caused by influenza A viruses (IAVs) is a major public health concern due to the high morbidity and notable mortality. Although there are several approved drugs targeting different mechanisms, the emergence of drug resistance calls for new drug candidates that can be used alone or in combinations. Small-molecule IAV entry inhibitor, ING-1466, binds to hemagglutinin (HA) and blocks HA-mediated viral infection. Here, we show that this inhibitor demonstrates preventive and therapeutic effects in a mouse model of IAV with substantial improvement in the survival rate. When administered orally it elicits a therapeutic effect in mice, even after the well-established infection. Moreover, the combination of ING-1466 with oseltamivir phosphate or baloxavir marboxil enhances the therapeutic effect in a synergistic manner. Overall, ING-1466 has excellent oral bioavailability and in vitro absorption, distribution, metabolism, excretion, and toxicity profile, suggesting that it can be developed for monotherapy or combination therapy for the treatment of IAV infections.

Discovery of a Macrocyclic Influenza Cap-Dependent Endonuclease Inhibitor.

Influenza viruses (IFVs) have caused several pandemics and have claimed numerous lives since their first record in the early 20th century. While the outbreak of COVID-19 seemed to expel influenza from the sight of people for a short period of time, it is not surprising that it will recirculate around the globe after the coronavirus has mutated into a less fatal variant. Baloxavir marboxil (1), the prodrug of baloxavir (2) and a cap-dependent endonuclease (CEN) inhibitor, were approved by the FDA for the first treatment in almost 20 years. Despite their high antiviral potency, drug-resistant variants have been observed in clinical trials. Herein, we report a novel CEN inhibitor 8 with a delicately designed macrocyclic scaffold that exhibits a significantly smaller shift of inhibitory activity toward baloxavir-resistant variants.

Structural Studies of Inhibitors with Clinically Relevant Influenza Endonuclease Variants.

Vital to the treatment of influenza is the use of antivirals such as Oseltamivir (Tamiflu) and Zanamivir (Relenza); however, antiviral resistance is becoming an increasing problem for these therapeutics. The RNA-dependent RNA polymerase acidic N-terminal (PAN) endonuclease, a critical component of influenza viral replication machinery, is an antiviral target that was recently validated with the approval of Baloxavir Marboxil (BXM). Despite its clinical success, BXM has demonstrated susceptibility to resistance mutations, specifically the I38T, E23K, and A36 V mutants of PAN. To better understand the effects of these mutations on BXM resistance and improve the design of more robust therapeutics, this study examines key differences in protein-inhibitor interactions with two inhibitors and the I38T, E23K, and A36 V mutants. Differences in inhibitor binding were evaluated by measuring changes in binding to PAN using two biophysical methods. The binding mode of two distinct inhibitors was determined crystallographically with both wild-type and mutant forms of PAN. Collectively, these studies give some insight into the mechanism of antiviral resistance of these mutants.

The impact of PA/I38 substitutions and PA polymorphisms on the susceptibility of zoonotic influenza A viruses to baloxavir.

Genetic reassortment of avian, swine, and human influenza A viruses (IAVs) poses potential pandemic risks. Surveillance is important for influenza pandemic preparedness, but the susceptibility of zoonotic IAVs to the cap-dependent endonuclease inhibitor baloxavir acid (BXA) has not been thoroughly researched. Although an amino acid substitution at position 38 in the polymerase acidic protein (PA/I38) in seasonal IAVs reduces BXA susceptibility, PA polymorphisms at position 38 are rarely seen in zoonotic IAVs. Here, we examined the impact of PA/I38 substitutions on the BXA susceptibility of recombinant A(H5N1) viruses. PA mutants that harbored I38T, F, and M were 48.2-, 24.0-, and 15.5-fold less susceptible, respectively, to BXA than wild-type A(H5N1) but were susceptible to the neuraminidase inhibitor oseltamivir acid and the RNA polymerase inhibitor favipiravir. PA mutants exhibited significantly impaired replicative fitness in Madin-Darby canine kidney cells at 24 h postinfection. In addition, in order to investigate new genetic markers for BXA susceptibility, we screened geographically and temporally distinct IAVs isolated worldwide from birds and pigs. The results showed that BXA exhibited antiviral activity against avian and swine viruses with similar levels to seasonal isolates. All viruses tested in the study lacked the PA/I38 substitution and were susceptible to BXA. Isolates harboring amino acid polymorphisms at positions 20, 24, and 37, which have been implicated in the binding of BXA to the PA endonuclease domain, were also susceptible to BXA. These results suggest that monitoring of the PA/I38 substitution in animal-derived influenza viruses is important for preparedness against zoonotic influenza virus outbreaks.

Genomic Analysis of Influenza A and B Viruses Carrying Baloxavir Resistance-Associated Substitutions Serially Passaged in Human Epithelial Cells.

Baloxavir marboxil (baloxavir) is an FDA-approved inhibitor of the influenza virus polymerase acidic (PA) protein. Here, we used next-generation sequencing to compare the genomic mutational profiles of IAV H1N1 and H3N2, and IBV wild type (WT) and mutants (MUT) viruses carrying baloxavir resistance-associated substitutions (H1N1-PA I38L, I38T, and E199D; H3N2-PA I38T; and IBV-PA I38T) during passaging in normal human bronchial epithelial (NHBE) cells. We determined the ratio of nonsynonymous to synonymous nucleotide mutations (dN/dS) and identified the location and type of amino acid (AA) substitutions that occurred at a frequency of ≥30%. We observed that IAV H1N1 WT and MUT viruses remained relatively stable during passaging. While the mutational profiles for IAV H1N1 I38L, I38T, and E199D, and IBV I38T MUTs were relatively similar after each passage compared to the respective WTs, the mutational profile of the IAV H3N2 I38T MUT was significantly different for most genes compared to H3N2 WT. Our work provides insight into how baloxavir resistance-associated substitutions may impact influenza virus evolution in natural settings. Further characterization of the potentially adaptive mutations identified in this study is needed.

Prophylactic Treatment with Baloxavir Protects Mice from Lethal Infection with Influenza A and B Viruses.

Influenza remains a worldwide health concern. Antiviral drugs are considered as one of the useful options for its prevention as a complementary measure to vaccination. Baloxavir acid selectively inhibits the cap-dependent endonuclease of influenza viruses and exhibits marked viral titre reduction in patients. Here, we describe the prophylactic potency of baloxavir acid against lethal infection with influenza A and B viruses in mice. BALB/c mice were subcutaneously administered once with baloxavir acid suspension, or orally administered once daily for 10 days with oseltamivir phosphate solution at human relevant doses. Next, the mice were intranasally inoculated with A/PR/8/34 (H1N1) or B/Hong Kong/5/72 strain at 24 to 96 h after the initial dosing. Prophylactic treatment with the antiviral drugs significantly reduced the lung viral titres and prolonged survival time. In particular, baloxavir acid showed a greater suppressive effect on lung viral titres compared to oseltamivir phosphate. In this model, baloxavir acid maintained significant prophylactic effects against influenza A and B virus infections when the plasma concentration at the time of infection was at least 0.88 and 3.58 ng/mL, respectively. The significant prophylactic efficacy observed in our mouse model suggests the potential utility of baloxavir marboxil for prophylaxis against influenza in humans.

A community cluster of influenza A(H3N2) virus infection with reduced susceptibility to baloxavir due to a PA E199G substitution in Japan, February to March 2023.

A community cluster of influenza A(H3N2) caused by viruses with an E199G substitution in PA was detected in Nara, Japan, between February and March 2023. The three patients with these mutant viruses had not received antiviral treatment before specimen collection but patients in the same hospital had. The sequences of the mutant viruses were closely related, suggesting clonal spread in Nara. They showed reduced susceptibility to baloxavir in vitro; however, the clinical significance of the PA E199G substitution remains unclear.

Impact of Baloxavir Resistance-Associated Substitutions on Influenza Virus Growth and Drug Susceptibility.

Baloxavir marboxil (baloxavir) is a recently FDA-approved influenza virus polymerase acidic (PA) endonuclease inhibitor. Several PA substitutions have been demonstrated to confer reduced susceptibility to baloxavir; however, their impacts on measurements of antiviral drug susceptibility and replication capacity when present as a fraction of the viral population have not been established. We generated recombinant A/California/04/09 (H1N1)-like viruses (IAV) with PA I38L, I38T, or E199D substitutions and B/Victoria/504/2000-like virus (IBV) with PA I38T. These substitutions reduced baloxavir susceptibility by 15.3-, 72.3-, 5.4-, and 54.5-fold, respectively, when tested in normal human bronchial epithelial (NHBE) cells. We then assessed the replication kinetics, polymerase activity, and baloxavir susceptibility of the wild-type:mutant (WT:MUT) virus mixtures in NHBE cells. The percentage of MUT relative to WT virus necessary to detect reduced baloxavir susceptibility in phenotypic assays ranged from 10% (IBV I38T) to 92% (IAV E199D). While I38T did not alter IAV replication kinetics or polymerase activity, IAV PA I38L and E199D MUTs and the IBV PA I38T MUT exhibited reduced replication levels and significantly altered polymerase activity. Differences in replication were detectable when the MUTs comprised ≥90%, ≥90%, or ≥75% of the population, respectively. Droplet digital PCR (ddPCR) and next-generation sequencing (NGS) analyses showed that WT viruses generally outcompeted the respective MUTs after multiple replication cycles and serial passaging in NHBE cells when initial mixtures contained ≥50% of the WT viruses; however, we also identified potential compensatory substitutions (IAV PA D394N and IBV PA E329G) that emerged and appeared to improve the replication capacity of baloxavir-resistant virus in cell culture. IMPORTANCE Baloxavir marboxil, an influenza virus polymerase acidic endonuclease inhibitor, represents a recently approved new class of influenza antivirals. Treatment-emergent resistance to baloxavir has been observed in clinical trials, and the potential spread of resistant variants could diminish baloxavir effectiveness. Here, we report the impact of the proportion of drug-resistant subpopulations on the ability to detect resistance in clinical isolates and the impact of substitutions on viral replication of mixtures containing both drug-sensitive and drug-resistant variants. We also show that ddPCR and NGS methods can be successfully used for detection of resistant subpopulations in clinical isolates and to quantify their relative abundance. Taken together, our data shed light on the potential impact of baloxavir-resistant I38T/L and E199D substitutions on baloxavir susceptibility and other biological properties of influenza virus and the ability to detect resistance in phenotypic and genotypic assays.

PA-E18G substitution in influenza A virus confers resistance to ZX-7101, a cap-dependent endonuclease inhibitor.

Cap-dependent endonuclease (CEN) in the polymerase acidic protein (PA) of influenza A virus (IAV) represents a promising drug target due to its critical role in viral gene transcription. The CEN inhibitor, baloxavir marboxil (BXM), was approved in Japan and the US in 2018 and several other countries subsequently. Along with the clinical use of BXM, the emergence and spread of IAV variants with reduced susceptibility to BXM have aroused serious concern. Herein, we comprehensively characterized the in vitro and in vivo antiviral activities of ZX-7101A, an analogue of BXM. The active form of prodrug ZX-7101 showed broad-spectrum antiviral potency against various IAV subtypes, including pH1N1, H3N2, H7N9 and H9N2, in MDCK cells, and the 50% effective concentration (EC50) was calculated to nanomole level and comparable to that of baloxavir acid (BXA), the active form of BXM. Furthermore, in vivo assays showed that administration of ZX-7101A conferred significant protection against lethal pH1N1 challenge in mice, with reduced viral RNA loads and alleviated pulmonary damage. Importantly, serial passaging of H1N1 virus in MDCK cells under selection pressure of ZX-7101 led to a resistant variant at the 15th passage. Reverse genetic and sequencing analysis demonstrated that a single E18G substitution in the PA subunit contributed to the reduced susceptibility to both ZX-7101 and BXA. Taken together, our results not only characterized a new CEN inhibitor of IAV but also identified a novel amino acid substitution responsible for CEN inhibitor resistance, which provides critical clues for future drug development and drug resistance surveillance.

In Vivo Antiviral Activity of Baloxavir against PA/I38T-Substituted Influenza A Viruses at Clinically Relevant Doses.

Although the prevalence of polymerase acidic (PA)/I38T strains of influenza virus with reduced susceptibility to baloxavir acid is low, there is a possibility of emergence under selective pressure. Furthermore, the virus may be transmitted between humans. We investigated the in vivo efficacy of baloxavir acid and oseltamivir phosphate against influenza A subtypes H1N1, H1N1pdm09, and H3N2, with PA/I38T substitution, at doses simulating human plasma concentrations. A pharmacokinetic/pharmacodynamic analysis was performed to strengthen the validity of the findings and the applicability in a clinical setting. Although the antiviral effect of baloxavir acid was attenuated in mice infected with PA/I38T-substituted viral strains compared with the wild type (WT), baloxavir acid significantly reduced virus titers at higher-but clinically relevant-doses. The virus titer reduction with baloxavir acid (30 mg/kg subcutaneous single dose) was comparable to that of oseltamivir phosphate (5 mg/kg orally twice daily) against H1N1 and H1N1pdm09 PA/I38T strains in mice, as well as the H3N2 PA/I38T strain in hamsters. Baloxavir acid demonstrated an antiviral effect against PA/I38T-substituted strains, at day 6, with no further viral rebound. In conclusion, baloxavir acid demonstrated dose-dependent antiviral effects comparable to that of oseltamivir phosphate, even though the degree of lung virus titer reduction was diminished in animal models infected with PA/I38T-substituted strains.

Investigating the transmission of baloxavir-resistant influenza viruses from treated index patients to untreated household contacts in the BLOCKSTONE study.

In a post-hoc analysis of the phase 3 BLOCKSTONE study (JapicCTI-184180), we investigated household transmission of baloxavir-resistant (PA/I38X) influenza viruses. Using baloxavir resistance rates from prior clinical trials and the rate of influenza transmission observed in the study, the predicted number of PA/I38X transmission events was 4.8, assuming wild type and PA/I38X viruses were equally transmissible. However, no PA/I38X viruses were observed. These results suggest a low potential for baloxavir-resistant influenza virus transmission from treated to untreated individuals, potentially due to reduced viral/transmission fitness for PA/I38X viruses and/or low viral titres at the time when resistant viruses arise.

Novel modelling approaches to predict the role of antivirals in reducing influenza transmission.

To aid understanding of the effect of antiviral treatment on population-level influenza transmission, we used a novel pharmacokinetic-viral kinetic transmission model to test the correlation between nasal viral load and infectiousness, and to evaluate the impact that timing of treatment with the antivirals oseltamivir or baloxavir has on influenza transmission. The model was run under three candidate profiles whereby infectiousness was assumed to be proportional to viral titer on a natural-scale, log-scale, or dose-response model. Viral kinetic profiles in the presence and absence of antiviral treatment were compared for each individual (N = 1000 simulated individuals); subsequently, viral transmission mitigation was calculated. The predicted transmission mitigation was greater with earlier administration of antiviral treatment, and with baloxavir versus oseltamivir. When treatment was initiated 12-24 hours post symptom onset, the predicted transmission mitigation was 39.9-56.4% for baloxavir and 26.6-38.3% for oseltamivir depending on the infectiousness profile. When treatment was initiated 36-48 hours post symptom onset, the predicted transmission mitigation decreased to 0.8-28.3% for baloxavir and 0.8-19.9% for oseltamivir. Model estimates were compared with clinical data from the BLOCKSTONE post-exposure prophylaxis study, which indicated the log-scale model for infectiousness best fit the observed data and that baloxavir affords greater reductions in secondary case rates compared with neuraminidase inhibitors. These findings suggest a role for baloxavir and oseltamivir in reducing influenza transmission when treatment is initiated within 48 hours of symptom onset in the index patient.

Effect of Baloxavir and Oseltamivir in Combination on Infection with Influenza Viruses with PA/I38T or PA/E23K Substitutions in the Ferret Model.

Amino acid substitutions I38T and E23K in the influenza polymerase acidic (PA) protein lead to reduced susceptibility to the influenza antiviral drug baloxavir. The in vivo effectiveness of baloxavir and oseltamivir for treatment of these viruses is currently unknown. Using patient-derived influenza isolates, combination therapy was equally effective as monotherapy in reducing viral titers in the upper respiratory tract of ferrets infected with A(H1N1pdm09)-PA/E23K or A(H3N2)-PA/I38T. When treated with baloxavir plus oseltamivir, infection with a mixture of PA/I38T or PA/E23K and corresponding wild-type virus was characterized by a lower selection of viruses with reduced baloxavir susceptibility over the course of infection compared to baloxavir monotherapy. De novo emergence of the oseltamivir resistance mutation NA/H275Y occurred in ferrets treated with oseltamivir alone but not in ferrets treated with baloxavir plus oseltamivir. Our data suggest that combination therapy with influenza drugs with different mechanisms of action decreased the selection pressure for viruses with reduced drug susceptibility. IMPORTANCE Influenza viruses cause significant morbidity and mortality worldwide but can be treated with antiviral drugs. In 2018, a highly effective antiviral drug, baloxavir marboxil, was licensed. However, the selection of viruses with baloxavir resistance was relatively high following treatment, which may compromise the effectiveness of the drug. Here, we took two different influenza viruses that are resistant to baloxavir and tested the effectiveness alone and in combination with oseltamivir (a second influenza antiviral drug) in the ferret model. Our findings suggest that combination treatment may be a more effective method than monotherapy to reduce the selection of resistant viruses. These results may have important clinical implications for the treatment of influenza.

Influenza A virus polymerase acidic protein E23G/K substitutions weaken key baloxavir drug-binding contacts with minimal impact on replication and transmission.

Baloxavir marboxil (BXM) is approved for treating uncomplicated influenza. The active metabolite baloxavir acid (BXA) inhibits cap-dependent endonuclease activity of the influenza virus polymerase acidic protein (PA), which is necessary for viral transcription. Treatment-emergent E23G or E23K (E23G/K) PA substitutions have been implicated in reduced BXA susceptibility, but their effect on virus fitness and transmissibility, their synergism with other BXA resistance markers, and the mechanisms of resistance have been insufficiently studied. Accordingly, we generated point mutants of circulating seasonal influenza A(H1N1)pdm09 and A(H3N2) viruses carrying E23G/K substitutions. Both substitutions caused 2- to 13-fold increases in the BXA EC50. EC50s were higher with E23K than with E23G and increased dramatically (138- to 446-fold) when these substitutions were combined with PA I38T, the dominant BXA resistance marker. E23G/K-substituted viruses exhibited slightly impaired replication in MDCK and Calu-3 cells, which was more pronounced with E23K. In ferret transmission experiments, all viruses transmitted to direct-contact and airborne-transmission animals, with only E23K+I38T viruses failing to infect 100% of animals by airborne transmission. E23G/K genotypes were predominantly stable during transmission events and through five passages in vitro. Thermostable PA-BXA interactions were weakened by E23G/K substitutions and further weakened when combined with I38T. In silico modeling indicated this was caused by E23G/K altering the placement of functionally important Tyr24 in the endonuclease domain, potentially decreasing BXA binding but at some cost to the virus. These data implicate E23G/K, alone or combined with I38T, as important markers of reduced BXM susceptibility, and such mutants could emerge and/or transmit among humans.

Effects of baloxavir and oseltamivir antiviral therapy on the transmission of seasonal influenza in China: A mathematical modeling analysis.

New antiviral influenza treatments can effectively alleviate illness while reducing viral shedding. However, how such effects can translate into lower population infections of seasonal influenza in China remains unknown. To shed light on the public health impacts of novel antiviral agents for influenza, we constructed a dynamic transmission model to simulate the seasonal influenza epidemics in China. Two antivirus treatments, baloxavir and oseltamivir, were evaluated by estimating their impacts on the incidences of influenza infection in a single flu season. In the base-case analysis of a 10% antiviral treatment uptake rate, 2760 and 3420 per 10 000 persons contracted influenza under the treatment of baloxavir and oseltamivir, respectively. These incidence rates amounted to an 18.90% relative risk reduction (RRR) of infection associated with baloxavir in relation to oseltamivir. The corresponding RRR was 82.16% when the antiviral treatment uptake rate was increased to 35%. In addition, the peak of the prevalence of infected individuals per 10 000 persons under the baloxavir treatment was 177 (range: 93-274) fewer than that of oseltamivir. Our analyses suggest that the baloxavir treatment strategy reduces the incidence of influenza in China compared with oseltamivir in the setting of a seasonal flu epidemic. Also, increasing the uptake rate of antiviral treatment can potentially prevent millions of infections during a single flu season.

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

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

Comparison of Intra-Familial Transmission of Influenza Virus From Index Patients Treated With Baloxavir Marboxil or Oseltamivir Using an Influenza Transmission Model and a Health Insurance Claims Database.

BACKGROUND: Influenza affects approximately a billion people globally, including > 10 million Japanese individuals every year. Baloxavir marboxil (baloxavir [BXM]; a selective cap-dependent endonuclease inhibitor) is approved for influenza treatment in Japan. We compared the incidence of intra-familial transmission of influenza between BXM and oseltamivir (OTV) treatments using a simulation model. METHODS: Using the JMDC Claims Database, we identified index case (IC) as the first family member diagnosed with influenza during the 2018-19 influenza season, and classified the families into BXM or OTV group per the drug dispensed to ICs. Using a novel influenza intra-familial infection model, we simulated the duration of influenza infection in ICs based on agent-specific virus shedding periods. Intra-familial infections were defined as non-IC family members infected during the agent-specific viral shedding period in ICs. The virus incubation periods in the non-IC family members were considered to exclude secondary infections from potentially external exposure. The primary endpoint was proportion of families with intra-familial infections. For between-group comparisons, we used a multivariate logistic regression model. RESULTS: The median proportion of families with intra-familial transmission was 9.57% and 19.35% in the BXM (N = 84 672) and OTV (N = 62 004) groups, respectively. The multivariate odds ratio of 1.73 (2.5th-97.5th percentiles, 1.68-1.77) indicated a substantially higher incidence of intra-familial infections in the OTV group versus the BXM group. Subgroup analyses by ICs' age category, virus type, and month of onset revealed similar trends favoring BXM. CONCLUSIONS: BXM treatment of ICs may contribute to a greater reduction in intra-familial influenza transmission than OTV treatment.

Comprehensive Evaluation of Biological Effects of Pentathiepins on Various Human Cancer Cell Lines and Insights into Their Mode of Action.

Pentathiepins are polysulfur-containing compounds that exert antiproliferative and cytotoxic activity in cancer cells, induce oxidative stress and apoptosis, and inhibit glutathione peroxidase (GPx1). This renders them promising candidates for anticancer drug development. However, the biological effects and how they intertwine have not yet been systematically assessed in diverse cancer cell lines. In this study, six novel pentathiepins were synthesized to suit particular requirements such as fluorescent properties or improved water solubility. Structural elucidation by X-ray crystallography was successful for three derivatives. All six underwent extensive biological evaluation in 14 human cancer cell lines. These studies included investigating the inhibition of GPx1 and cell proliferation, cytotoxicity, and the induction of ROS and DNA strand breaks. Furthermore, selected hallmarks of apoptosis and the impact on cell cycle progression were studied. All six pentathiepins exerted high cytotoxic and antiproliferative activity, while five also strongly inhibited GPx1. There is a clear connection between the potential to provoke oxidative stress and damage to DNA in the form of single- and double-strand breaks. Additionally, these studies support apoptosis but not ferroptosis as the mechanism of cell death in some of the cell lines. As the various pentathiepins give rise to different biological responses, modulation of the biological effects depends on the distinct chemical structures fused to the sulfur ring. This may allow for an optimization of the anticancer activity of pentathiepins in the future.

Detection of Variants With Reduced Baloxavir Marboxil and Oseltamivir Susceptibility in Children With Influenza A During the 2019-2020 Influenza Season.

BACKGROUND: We aimed to detect influenza variants with reduced susceptibility to baloxavir marboxil (baloxavir) and oseltamivir and identify differences in the clinical course between children with and without these variants after antiviral treatment. METHODS: During the 2019-2020 influenza season, we enrolled children with confirmed influenza A (20 treated with baloxavir and 16 with oseltamivir). We analyzed patients' sequential viral RNA loads and infectious virus titers, the drug susceptibilities of clinical isolates, and amino acid substitutions in the viral polymerase acidic protein subunits or neuraminidase. We assessed patients' clinical information using questionnaires. RESULTS: All viral RNA loads and virus titers were significantly decreased after treatment, but we detected baloxavir-resistant and oseltamivir-resistant variants in 5 of 20 and 3 of 16 patients, respectively. The duration of fever was similar between patients with and without the variants, but infectious viral shedding lasted 3 days longer in patients with baloxavir-resistant variants. In addition, the duration to improvement of clinical symptoms was longer in these patients (75.0 vs 29.5 hours; P = .106). CONCLUSIONS: After antiviral treatment, the emergence of baloxavir-resistant variants may affect the patients' clinical course, but oseltamivir-resistant variants had no clinical impact.

Modeling mitigation of influenza epidemics by baloxavir.

Influenza viruses annually kill 290,000-650,000 people worldwide. Antivirals can reduce death tolls. Baloxavir, the recently approved influenza antiviral, inhibits initiation of viral mRNA synthesis, whereas oseltamivir, an older drug, inhibits release of virus progeny. Baloxavir blocks virus replication more rapidly and completely than oseltamivir, reducing the duration of infectiousness. Hence, early baloxavir treatment may indirectly prevent transmission. Here, we estimate impacts of ramping up and accelerating baloxavir treatment on population-level incidence using a new model that links viral load dynamics from clinical trial data to between-host transmission. We estimate that ~22 million infections and >6,000 deaths would have been averted in the 2017-2018 epidemic season by administering baloxavir to 30% of infected cases within 48 h after symptom onset. Treatment within 24 h would almost double the impact. Consequently, scaling up early baloxavir treatment would substantially reduce influenza morbidity and mortality every year. The development of antivirals against the SARS-CoV2 virus that function like baloxavir might similarly curtail transmission and save lives.