Baloxavir Marboxil Single-dose Treatment in Influenza-infected Children: A Randomized, Double-blind, Active Controlled Phase 3 Safety and Efficacy Trial (miniSTONE-2)

Duration of fever in children infected with influenza A(H1N1)pdm09, A(H3N2) or B virus and treated with baloxavir marboxil, oseltamivir, laninamivir, or zanamivir in Japan during the 2012-2013 and 2019-2020 influenza seasons

We compared the duration of fever in children infected with A(H1N1)pdm09, A(H3N2), or influenza B viruses following treatment with baloxavir marboxil (baloxavir) or neuraminidase inhibitors (NAIs) (oseltamivir, zanamivir, or laninamivir). This observational study was conducted at 10 outpatient clinics across 9 prefectures in Japan during the 2012-2013 and 2019-2020 influenza seasons. Patients with influenza rapid antigen test positive were treated with one of four anti-influenza drugs. The type/subtype of influenza viruses were identified from MDCK or MDCK SIAT1 cell-grown samples using two-step real-time PCR. Daily self-reported body temperature after treatment were used to evaluate the duration of fever by treatment group and various underlying factors. Among 1,742 patients < 19 years old analyzed, 452 (26.0%) were A(H1N1)pdm09, 827 (48.0%) A(H3N2), and 463 (26.0%) influenza B virus infections. Among fours treatment groups, baloxavir showed a shorter median duration of fever compared to oseltamivir in univariate analysis for A(H1N1)pdm09 virus infections (baloxavir, 22.0 h versus oseltamivir, 26.7 h, P < 0.05; laninamivir, 25.5 h, and zanamivir, 25.0 h). However, this difference was not significant in multivariable analyses. For A(H3N2) virus infections, there were no statistically significant differences observed (20.3, 21.0, 22.0, and 19.0 h) uni- and multivariable analyses. For influenza B, baloxavir shortened the fever duration by approximately 15 h than NAIs (20.3, 35.0, 34.3, and 34.1 h), as supported by uni- and multivariable analyses. Baloxavir seems to have comparable clinical effectiveness with NAIs on influenza A but can be more effective for treating pediatric influenza B virus infections than NAIs.

Comparative Effectiveness of Baloxavir Marboxil and Oseltamivir Treatment in Reducing Household Transmission of Influenza: A Post Hoc Analysis of the BLOCKSTONE Trial

BACKGROUND

The transmission of influenza virus in households, especially by children, is a major route of infection. Prior studies suggest that timely antiviral treatment of ill cases may reduce infection in household contacts. The aim of the study was to compare the effects of oseltamivir (OTV) and baloxavir marboxil (BXM) treatment of index cases on the secondary attack rate (SAR) of influenza within household.

METHODS

A post hoc analysis was done in BLOCKSTONE trial-a placebo-controlled, double-blinded post-exposure prophylaxis of BXM. Data were derived from the laboratory-confirmed index cases' household contacts who received placebo in the trial and also from household members who did not participate in the trial but completed illness questionnaires. To assess the SAR of household members, multivariate analyses adjusted for factors including age, vaccination status, and household size were performed and compared between contacts of index cases treated with BXM or OTV.

RESULTS

In total, 185 index cases (116 treated with BXM and 69 treated with OTV) and 410 household contacts (201 from trial, 209 by questionnaire) were included. The Poisson regression modeling showed that the SAR in household contacts of index cases treated with BXM and OTV was 10.8% and 18.5%, respectively; the adjusted relative reduction in SAR was 41.8% (95% confidence interval: 1.0%-65.7%, p = 0.0456) greater with BXM than OTV. Similar reductions were found in contacts from the trial and those included by questionnaire.

CONCLUSION

BXM treatment of index cases appeared to result in a greater reduction in secondary household transmission than OTV treatment.

Comparison of clinical efficacy and safety of baloxavir marboxil versus oseltamivir as the treatment for influenza virus infections: A systematic review and meta-analysis

INTRODUCTION

Baloxavir marboxil (BXM), a newly developed cap-dependent endonuclease inhibitor, is widely used to treat influenza virus infections in inpatients and outpatients. A previous meta-analysis included only outpatients and patients suspected of having an influenza virus infection based on clinical symptoms. However, whether BXM or oseltamivir is safer and more effective for inpatients remains controversial. Therefore, we conducted a systematic review and meta-analysis validating the effectiveness and safety of BXM versus oseltamivir in inpatients with influenza virus.

METHODS

The Scopus, EMBASE, PubMed, Ichushi, and CINAHL databases were systematically searched for articles published until January 2023. The outcomes were mortality, hospitalization period, incidence of BXM- or oseltamivir-related adverse events, illness duration, and changes of virus titers and viral RNA load in patients with influenza virus infections.

RESULTS

Two randomized controlled trials with 1624 outpatients and two retrospective studies with 874 inpatients were enrolled. No deaths occurred in outpatients treated with BXM or oseltamivir. Among inpatients, BXM reduced mortality (p = 0.06) and significantly shortened hospitalization period (p = 0.01) compared to oseltamivir. In outpatients, BXM had a significantly lower incidence of adverse events (p = 0.03), reductions in influenza virus titers (p < 0.001) and viral RNA loads (p < 0.001), and a tendency to be a shorter illness duration compared with that of oseltamivir (p = 0.27).

CONCLUSIONS

Our meta-analysis showed that BXM was safer and more effective in patients than oseltamivir; thus, supporting the use of BXM for the initial treatment of patients with proven influenza virus infection.

Influenza A virus resistance to 4'-fluorouridine coincides with viral attenuation in vitro and in vivo

Pre-existing or rapidly emerging resistance of influenza viruses to approved antivirals makes the development of novel therapeutics to mitigate seasonal influenza and improve preparedness against future influenza pandemics an urgent priority. We have recently identified the chain-terminating broad-spectrum nucleoside analog clinical candidate 4'-fluorouridine (4'-FlU) and demonstrated oral efficacy against seasonal, pandemic, and highly pathogenic avian influenza viruses in the mouse and ferret model. Here, we have resistance-profiled 4'-FlU against a pandemic A/CA/07/2009 (H1N1) (CA09). In vitro viral adaptation yielded six independently generated escape lineages with distinct mutations that mediated moderate resistance to 4'-FlU in the genetically controlled background of recombinant CA09 (recCA09). Mutations adhered to three distinct structural clusters that are all predicted to affect the geometry of the active site of the viral RNA-dependent RNA polymerase (RdRP) complex for phosphodiester bond formation. Escape could be achieved through an individual causal mutation, a combination of mutations acting additively, or mutations functioning synergistically. Fitness of all resistant variants was impaired in cell culture, and all were attenuated in the mouse model. Oral 4'-FlU administered at lowest-efficacious (2 mg/kg) or elevated (10 mg/kg) dose overcame moderate resistance when mice were inoculated with 10 LD50 units of parental or resistant recCA09, demonstrated by significantly reduced virus load and complete survival. In the ferret model, invasion of the lower respiratory tract by variants representing four adaptation lineages was impaired. Resistant variants were either transmission-incompetent, or spread to untreated sentinels was fully blocked by therapeutic treatment of source animals with 4'-FlU.

Approach to hematopoietic cell transplant candidates with respiratory viral detection

The management of respiratory viruses prior to hematopoietic cell transplant (HCT) can be controversial and requires special consideration of host factors, transplant parameters, and the specific respiratory virus (RV). In the setting of adenovirus (ADV), human metapneumovirus (HMPV), influenza, parainfluenza virus (PIV), and respiratory syncytial virus (RSV) detection prior to hematopoietic cell transplant (HCT), clinical practice guidelines recommend transplant delay when possible; however, there is much more ambiguity when other respiratory viruses, such as seasonal coronaviruses (CoVs), human rhinovirus (HRV), and SARS-CoV-2, are detected. Our aims for this review include detailing clinical practical guidelines and reviewing current literature on pre-transplant respiratory viral infections (RVIs), including antiviral therapies and prevention strategies, when available. We will center our discussion on three representative clinical scenarios, with the goal of providing practical guidance to clinicians.

Safety and Efficacy of Baloxavir Marboxil in Influenza-infected Children 5-11 Years of Age: A Post Hoc Analysis of a Phase 3 Study

BACKGROUND

miniSTONE-2 (NCT03629184) was a global, phase 3, randomized, controlled study that investigated the safety and efficacy of single-dose baloxavir marboxil in otherwise healthy children 1-<12 years of age and showed a positive risk-benefit profile. This post hoc analysis evaluated the safety and efficacy of baloxavir versus oseltamivir in children 5-11 years old with influenza.

METHODS

Children received single-dose baloxavir or twice-daily oseltamivir for 5 days. Safety was the primary objective. Efficacy and virological outcomes included time to alleviation of symptoms, duration of fever and time to cessation of viral shedding by titer. Data were summarized descriptively.

RESULTS

Ninety-four children 5-11 years old were included (61 baloxavir and 33 oseltamivir). Baseline characteristics were similar between the groups. The incidence of adverse events was balanced and low in both treatment groups, with the most common being vomiting (baloxavir 5% vs. oseltamivir 18%), diarrhea (5% vs. 0%) and otitis media (0% vs. 5%). No serious adverse events or deaths occurred. Median (95% CI) time to alleviation of symptoms with baloxavir was 138.4 hours (116.7-163.4) versus 126.1 hours (95.9-165.7) for oseltamivir; duration of fever was comparable between groups [41.2 hours (23.5-51.4) vs. 51.3 hours (30.7-56.8), respectively]. Median time to cessation of viral shedding was shorter in the baloxavir group versus oseltamivir (1 vs. ≈3 days).

CONCLUSIONS

Safety, efficacy and virological results in children 5-11 years were similar to those from the overall study population 1-<12 years of age. Single-dose baloxavir provides an additional treatment option for pediatric patients 5-11 years old with influenza.

Influenza in Children and Adolescents: Epidemiology, Management, and Prevention

EDUCATION GAP

Influenza is among the most common infectious causes of pediatric emergency department visits and hospitalizations. Clinicians should use evidence-based guidelines to learn how to identify, manage, prevent, and treat influenza cases. Disease caused by influenza virus can be mitigated with appropriate treatment and prevention efforts.

OBJECTIVES After completing this article, readers should be able to:

1. Describe the virology and epidemiology of influenza.

2. List the clinical features and complications of influenza infections.

3. List the benefits and limitations of testing modalities for the diagnosis of influenza.

4. Appropriately apply American Academy of Pediatrics, Infectious Diseases Society of America, and Centers for Disease Control and Prevention (CDC) treatment guidelines for influenza or suspected influenza.

5. Describe the importance of influenza vaccination.

Influenza A virus resistance to 4'-fluorouridine coincides with viral attenuation in vitro and in vivo

Pre-existing or rapidly emerging resistance of influenza viruses to approved antivirals makes the development of novel therapeutics to mitigate seasonal influenza and improve preparedness against future influenza pandemics an urgent priority. We have recently identified the chain-terminating broad-spectrum nucleoside analog clinical candidate 4'-fluorouridine (4'-FlU) and demonstrated oral efficacy against seasonal, pandemic, and highly pathogenic avian influenza viruses in the mouse and ferret model. Here, we have resistance-profiled 4'-FlU against a pandemic A/CA/07/2009 (H1N1) (CA09). In vitro viral adaptation yielded six independently generated escape lineages with distinct mutations that mediated moderate resistance to 4'-FlU in the genetically controlled background of recombinant CA09 (recCA09). Mutations adhered to three distinct structural clusters that are all predicted to affect the geometry of the active site of the viral RNA-dependent RNA polymerase (RdRP) complex for phosphodiester bond formation. Escape could be achieved through an individual causal mutation, a combination of mutations acting additively, or mutations functioning synergistically. Fitness of all resistant variants was impaired in cell culture, and all were attenuated in the mouse model. Oral 4'-FlU administered at lowest-efficacious (2 mg/kg) or elevated (10 mg/kg) dose overcame moderate resistance when mice were inoculated with 10 LD 50 units of parental or resistant recCA09, demonstrated by significantly reduced virus load and complete survival. In the ferret model, invasion of the lower respiratory tract by variants representing four adaptation lineages was impaired. Resistant variants were either transmission-incompetent, or spread to untreated sentinels was fully blocked by therapeutic treatment of source animals with 4'-FlU.

Author Summary

Reduced sensitivity to FDA-approved influenza drugs is a major obstacle to effective antiviral therapy. We have previously demonstrated oral efficacy of a novel clinical candidate drug, 4'-FlU, against seasonal, pandemic, and highly pathogenic avian influenza viruses. In this study, we have determined possible routes of influenza virus escape from 4'-FlU and addressed whether resistance imposes a viral fitness penalty, affecting pathogenicity or ability to transmit. We identified three distinct clusters of mutations that lead to moderately reduced viral sensitivity to the drug. Testing of resistant variants against two chemically unrelated nucleoside analog inhibitors of influenza virus, conditionally approved favipiravir and the broad-spectrum SARS-CoV-2 drug molnupiravir, revealed cross-resistance of one cluster with favipiravir, whereas no viral escape from molnupiravir was noted. We found that the resistant variants are severely attenuated in mice, impaired in their ability to invade the lower respiratory tract and cause viral pneumonia in ferrets, and transmission-defective or compromised. We could fully mitigate lethal infection of mice with the resistant variants with standard or 5-fold elevated oral dose of 4'-FlU. These results demonstrate that partial viral escape from 4'-FlU is feasible in principle, but escape mutation clusters are unlikely to reach clinical significance or persist in circulating influenza virus strains.

Recommendations for Prevention and Control of Influenza in Children, 2023-2024

This technical report accompanies the recommendations of the American Academy of Pediatrics for the routine use of influenza vaccine and antiviral medications in the prevention and treatment of influenza in children during the 2023-2024 season. The rationale for the American Academy of Pediatrics recommendation for annual influenza vaccination of all children without medical contraindications starting at 6 months of age is provided. Influenza vaccination is an important strategy for protecting children and the broader community against influenza. This technical report summarizes recent influenza seasons, morbidity and mortality in children, vaccine effectiveness, and vaccination coverage, and provides detailed guidance on vaccine storage, administration, and implementation. The report also provides a brief background on inactivated and live-attenuated influenza vaccines, available vaccines this season, vaccination during pregnancy and breastfeeding, diagnostic testing for influenza, and antiviral medications for treatment and chemoprophylaxis. Strategies to promote vaccine uptake are emphasized.

Management of influenza - updated Swedish guidelines for antiviral treatment

Influenza causes seasonal epidemics of respiratory infection in all parts of the world. Manifestations of influenza range from mild upper to severe lower respiratory tract infection. Medical risk groups are defined by factors predisposing for development of severe disease and are recommended annual vaccination as a protective measure. The previous Swedish treatment guidelines for influenza were issued in 2011, and a review of current evidence was deemed relevant. An important reason to revisit the guidelines is the recent approval of a novel drug for influenza treatment, baloxavir. Updated Swedish evidence-based guidelines created by a group of experts from various research areas, for the management of influenza are presented here. The work has been made in collaboration with the Public Health Agency of Sweden and the Swedish Reference Group for AntiViral therapy (RAV). The updated guidelines include guidelines for diagnostics, treatment and prophylaxis in special groups, including management of pregnant women and children with influenza. A new section about infection control has been added. Pharmacological treatment is covered in detail with regards to indication and dosage. Additionally, drug resistance and environmental aspects are discussed.

Early Fever Resolution in Early Childhood Influenza Treated with Baloxavir Marboxil: A Retrospective Study Compared to Those with Oseltamivir

Background and Objectives: Baloxavir marboxil is a novel cap-dependent endonuclease inhibitor prescribed for influenza treatment. Unlike neuraminidase inhibitors like oseltamivir, which impair viral release from infected host cells, baloxavir blocks influenza virus proliferation by inhibiting viral mRNA transcription. This study aimed to compare the effectiveness of baloxavir and oseltamivir for the treatment of early childhood influenza. Materials and Methods: Of 1410 patients diagnosed with influenza between 2015 and 2018 at a Japanese primary care outpatient clinic, 1111 pediatric patients aged 0-6 years who were treated with baloxavir (n = 555) or oseltamivir (n = 556) were enrolled retrospectively. The following clinical factors were compared between patients treated with baloxavir and oseltamivir: age, sex, time from fever onset to drug administration (<24 h or 24-48 h), time from drug administration to fever reduction, influenza type (A or B), and influenza vaccination before disease onset. The duration of the fever, which was used as an index of clinical effectiveness, was compared using the log-rank test. Clinical factors associated with fever duration were determined using multivariate logistic regression analysis. Results: Median age (3.0 vs. 2.5 years), influenza type A (99% vs. 47%), median duration from drug administration to fever resolution (1 day vs. 2 days), and influenza vaccination (done, 41% vs. not done, 65%) were significantly different between the baloxavir and oseltamivir groups (p < 0.001). The number of patients with a fever duration of one day was 553 (99.6%) in the baloxavir group and 6 (1.1%) in the oseltamivir group (p < 0.001). Baloxavir use was only significantly associated with fever duration in the multivariate analysis (odds ratio 50,201, p < 0.001). Apparent adverse effects were not observed in the baloxavir-treated group. Conclusions: Baloxavir treatment resulted in a shorter fever duration than oseltamivir treatment in early childhood influenza.

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.

Factors associated with viral RNA shedding and evaluation of potential viral infectivity at returning to school in influenza outpatients after treatment with baloxavir marboxil and neuraminidase inhibitors during 2013/2014-2019/2020 seasons in Japan: an observational study

BACKGROUND

This study assessed the differences in daily virus reduction and the residual infectivity after the recommended home stay period in Japan in patients infected with influenza and treated with baloxavir (BA), laninamivir (LA), oseltamivir (OS), and zanamivir (ZA).

METHODS

We conducted an observational study on children and adults at 13 outpatient clinics in 11 prefectures in Japan during seven influenza seasons from 2013/2014 to 2019/2020. Virus samples were collected twice from influenza rapid test-positive patients at the first and second visit 4-5 days after the start of treatment. The viral RNA shedding was quantified using quantitative RT-PCR. Neuraminidase (NA) and polymerase acidic (PA) variant viruses that reduce susceptibility to NA inhibitors and BA, respectively, were screened using RT-PCR and genetic sequencing. Daily estimated viral reduction was evaluated using univariate and multivariate analyses for the factors such as age, treatment, vaccination status, or the emergence of PA or NA variants. The potential infectivity of the viral RNA shedding at the second visit samples was determined using the Receiver Operator Curve based on the positivity of virus isolation.

RESULTS

Among 518 patients, 465 (80.0%) and 116 (20.0%) were infected with influenza A (189 with BA, 58 with LA, 181 with OS, 37 with ZA) and influenza B (39 with BA, 10 with LA, 52 with OS, 15 with ZA). The emergence of 21 PA variants in influenza A was detected after BA treatment, but NA variants were not detected after NAIs treatment. Multiple linear regression analysis showed that the daily viral RNA shedding reduction in patients was slower in the two NAIs (OS and LA) than in BA, influenza B infection, aged 0-5 years, or the emergence of PA variants. The residual viral RNA shedding potentially infectious was detected in approximately 10-30% of the patients aged 6-18 years after five days of onset.

CONCLUSIONS

Viral clearance differed by age, type of influenza, choice of treatment, and susceptibility to BA. Additionally, the recommended homestay period in Japan seemed insufficient, but reduced viral spread to some extent since most school-age patients became non-infectious after 5 days of onset.

Preparing for the Next Influenza Season: Monitoring the Emergence and Spread of Antiviral Resistance

Purpose

The relaxation of pandemic restrictions in 2022 has led to a reemergence of respiratory virus circulation worldwide and anticipation of substantial influenza waves for the 2022/2023 Northern Hemisphere winter. Therefore, the antiviral susceptibility profiles of human influenza viruses circulating in Germany were characterized.

Methods

Between October 2019 (week 40/2019) and March 2022 (week 12/2022), nasal swabs from untreated patients with acute respiratory symptoms were collected in the national German influenza surveillance system. A total of 598 influenza viruses were isolated and analyzed for susceptibility to oseltamivir, zanamivir and peramivir, using a neuraminidase (NA) inhibition assay. In addition, next-generation sequencing was applied to assess molecular markers of resistance to NA, cap-dependent endonuclease (PA) and M2 ion channel inhibitors (NAI, PAI, M2I) in 367 primary clinical samples. Furthermore, a genotyping assay based on RT-PCR and pyrosequencing to rapidly assess the molecular resistance marker PA-I38X in PA genes was designed and established.

Results

While NAI resistance in the strict sense, defined by a ≥ 10-fold (influenza A) or ≥5-fold (influenza B) increase of NAI IC₅₀, was not detected, a subtype A(H1N1)pdm09 isolate displayed 2.3- to 7.5-fold IC₅₀ increase for all three NAI. This isolate carried the NA-S247N substitution, which is known to enhance NAI resistance induced by NA-H275Y. All sequenced influenza A viruses carried the M2-S31N substitution, which confers resistance to M2I. Of note, one A(H3N2) virus displayed the PA-I38M substitution, which is associated with reduced susceptibility to the PAI baloxavir marboxil. Pyrosequencing analysis confirmed these findings in the original clinical specimen and in cultured virus isolate, suggesting sufficient replicative fitness of this virus mutant.

Conclusion

Over the last three influenza seasons, the vast majority of influenza viruses in this national-level sentinel were susceptible to NAIs and PAIs. These findings support the use of antivirals in the upcoming influenza season.

Chemical scaffold recycling: Structure-guided conversion of an HIV integrase inhibitor into a potent influenza virus RNA-dependent RNA polymerase inhibitor designed to minimize resistance potential

Influenza is one of the leading causes of disease-related mortalities worldwide. Several strategies have been implemented during the past decades to hinder the replication cycle of influenza viruses, all of which have resulted in the emergence of resistant virus strains. The most recent example is baloxavir marboxil, where a single mutation in the active site of the target endonuclease domain of the RNA-dependent-RNA polymerase renders the recent FDA approved compound ∼1000-fold less effective. Raltegravir is a first-in-class HIV inhibitor that shows modest activity to the endonuclease. Here, we have used structure-guided approaches to create rationally designed derivative molecules that efficiently engage the endonuclease active site. The design strategy was driven by our previously published structures of endonuclease-substrate complexes, which allowed us to target functionally conserved residues and reduce the likelihood of resistance mutations. We succeeded in developing low nanomolar equipotent inhibitors of both wild-type and baloxavir-resistant endonuclease. We also developed macrocyclic versions of these inhibitors that engage the active site in the same manner as their 'open' counterparts but with reduced affinity. Structural analyses provide clear avenues for how to increase the affinity of these cyclic compounds.

Baloxavir safety and clinical and virologic outcomes in influenza virus-infected pediatric patients by age group: age-based pooled analysis of two pediatric studies conducted in Japan

BACKGROUND

Anti-influenza treatment is important for children and is recommended in many countries. This study assessed safety, clinical, and virologic outcomes of baloxavir marboxil (baloxavir) treatment in children based on age and influenza virus type/subtype.

METHODS

This was a post hoc pooled analysis of two open-label non-controlled studies of a single weight-based oral dose of baloxavir (day 1) in influenza virus-infected Japanese patients aged < 6 years (n = 56) and ≥ 6 to < 12 years (n = 81). Safety, time to illness alleviation (TTIA), time to resolution of fever (TTRF), recurrence of influenza illness symptoms and fever (after day 4), virus titer, and outcomes by polymerase acidic protein variants at position I38 (PA/I38X) were evaluated.

RESULTS

Adverse events were reported in 39.0 and 39.5% of patients < 6 years and ≥ 6 to < 12 years, respectively. Median (95% confidence interval) TTIA was 43.2 (36.3-68.4) and 45.4 (38.9-61.0) hours, and TTRF was 32.2 (26.8-37.8) and 20.7 (19.2-23.8) hours, for patients < 6 years and ≥ 6 to < 12 years, respectively. Symptom and fever recurrence was more common in patients < 6 years with influenza B (54.5 and 50.0%, respectively) compared with older patients (0 and 25.0%, respectively). Virus titers declined (day 2) for both age groups. Transient virus titer increase and PA/I38X-variants were more common for patients < 6 years.

CONCLUSIONS

The safety and effectiveness of single-dose baloxavir were observed in children across all age groups and influenza virus types. Higher rates of fever recurrence and transient virus titer increase were observed in children < 6 years.

TRIAL REGISTRATION

Japan Pharmaceutical Information Center Clinical Trials Information JapicCTI-163,417 (registered 02 November 2016) and JapicCTI-173,811 (registered 15 December 2017).

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.

Progression of Antiviral Agents Targeting Viral Polymerases

Viral DNA and RNA polymerases are two kinds of very important enzymes that synthesize the genetic materials of the virus itself, and they have become extremely favorable targets for the development of antiviral drugs because of their relatively conserved characteristics. There are many similarities in the structure and function of different viral polymerases, so inhibitors designed for a certain viral polymerase have acted as effective universal inhibitors on other types of viruses. The present review describes the development of classical antiviral drugs targeting polymerases, summarizes a variety of viral polymerase inhibitors from the perspective of chemically synthesized drugs and natural product drugs, describes novel approaches, and proposes promising development strategies for antiviral drugs.

Recommendations for Prevention and Control of Influenza in Children, 2022-2023

This technical report accompanies the recommendations of the American Academy of Pediatrics for the routine use of influenza vaccine and antiviral medications in the prevention and treatment of influenza in children during the 2022 to 2023 season. The American Academy of Pediatrics recommends annual influenza vaccination of all children without medical contraindications starting at 6 months of age. Influenza vaccination is an important strategy for protecting children and the broader community as well as reducing the overall burden of respiratory illnesses when other viruses, including severe acute respiratory syndrome-coronavirus 2, are cocirculating. This technical report summarizes recent influenza seasons, morbidity and mortality in children, vaccine effectiveness, and vaccination coverage, and provides detailed guidance on storage, administration, and implementation. The report also provides a brief background on inactivated and live attenuated influenza vaccine recommendations, vaccination during pregnancy and breastfeeding, diagnostic testing, and antiviral medications for treatment and chemoprophylaxis. Updated information is provided about the 2021 to 2022 influenza season, influenza immunization rates, the effectiveness of influenza vaccination on hospitalization and mortality, available vaccines, guidance for patients with history of severe allergic reactions to prior influenza vaccinations, and strategies to promote vaccine uptake.

Efficacy and safety of single-dose antiviral drugs for influenza treatment: A systematic review and network meta-analysis

To conduct network meta-analysis (NMA) of clinical efficacy and safety of single-dose antiviral drugs, grouped by dosage, in treatment of influenza. Systematic retrievals were conducted in databases, including Pubmed, Embase, Web of Science, the Cochrane Register of Clinical Trials and from the website ClinicalTrials.gov, for clinical trials recorded between the interception of the databases and March 31, 2021. Randomized controlled trials (RCTs) of influenza treatment in which single-dose antiviral drugs were administered were selected according to preset inclusion and exclusion criteria by two researchers who screened the literature independently from each other. The quality of the included studies was assessed using the Cochrane bias risk assessment tool. Software such as Stata 16.0 and Review Manager 5.3 was adopted for statistical analysis. Pairwise meta-analysis and NMA were carried out under the random-effects model. For both binary and continuous variables, odds ratio (OR), mean difference (MD) and their 95% confidence intervals (CI) were used to rank treatment efficiencies and analyze the differences. A total of 12 RCTs involving 7296 participants were included in the analysis. According to the NMA results, peramivir 300 mg (MD = -17.68, 95% CI: [-34.05, -1.32]), peramivir 600 mg (MD = -16.15, 95% CI: [-29.35, -2.95]), baloxavir (MD = -14.67, 95% CI: [-26.75, -2.58]) and laninamivir 40 mg (MD = -12.42, 95% CI: [-22.53, -2.31]) remarkably outperformed laninamivir 20 mg in time to alleviation of symptoms (TTAS). However, no intervention statistically outperform others in antipyretic time, virus titer variations against the baseline 24 and 48 h after medication and adverse events (AEs). The efficacy rankings were: peramivir 300 mg (the surface under the cumulative ranking curve [SUCRA] = 80.3%) > peramivir 600 mg (SUCRA = 76.2%) > baloxavir (SUCRA = 68.4%) > laninamivir 40 mg (SUCRA = 55.0%) > laninamivir 20 mg (SUCRA = 16.6%) for TTAS; baloxavir (SUCRA = 76.3%) > peramivir 600 mg (SUCRA = 67.8%) > laninamivir 40 mg (SUCRA = 47.2%) > laninamivir 20 mg (SUCRA = 40.0%) for antipyretic time; baloxavir (SUCRA = 96.7%) > peramivir 300 mg (SUCRA = 64.5%) ≈ peramivir 600 mg (SUCRA = 63.2%), baloxavir (SUCRA = 93.2%) > peramivir 600 mg (SUCRA = 64.0%) ≈ peramivir 300 mg (SUCRA = 55.0%), for virus titer variations against the baseline 24 and 48 h after medication, respectively; and baloxavir (SUCRA = 83.4%) > peramivir 300 mg (SUCRA = 71.4%) > laninamivir 20 mg (SUCRA = 62.4%) > peramivir 600 mg (SUCRA = 56.2%) > laninamivir 40 mg (SUCRA = 36.8%) for adverse events. Among the single-dose anti-influenza virus drugs compared, peramivir is superior to baloxavir and laninamivir in TTAS, whereas baloxavir has the best efficacy in antipyretic time, virus titer variations against the baseline 24 and 48 h after medication and AEs. This study has been registered in the International Prospective Register of Systematic Reviews (PROSPERO), with a registration number of CRD42021238220.

Influenza antivirals and animal models

Influenza A and B viruses are among the most prominent human respiratory pathogens. About 3-5 million severe cases of influenza are associated with 300 000-650 000 deaths per year globally. Antivirals effective at reducing morbidity and mortality are part of the first line of defense against influenza. FDA-approved antiviral drugs currently include adamantanes (rimantadine and amantadine), neuraminidase inhibitors (NAI; peramivir, zanamivir, and oseltamivir), and the PA endonuclease inhibitor (baloxavir). Mutations associated with antiviral resistance are common and highlight the need for further improvement and development of novel anti-influenza drugs. A summary is provided for the current knowledge of the approved influenza antivirals and antivirals strategies under evaluation in clinical trials. Preclinical evaluations of novel compounds effective against influenza in different animal models are also discussed.

Kinetic degradation study for the first licenced anti-influenza polymerase inhibitor, baloxavir marboxil, using HPLC-MS

The first licensed polymerase inhibitor, baloxavir marboxil was recently approved for the treatment of influenza A and B viruses. Furthermore, there is growing interest in testing the antiviral activity of baloxavir marboxil against Coronavirus. Despite its critical clinical value, there is no information on the degradation products, pathways or kinetics of baloxavir marboxil under various stress conditions. In this study, a new HPLC-MS chromatographic method for accurately quantifying baloxavir marboxil in the presence of its degradation products was developed. A study of degradation kinetics revealed that acidic, thermal neutral, and photolytic degradation reactions have zero-order kinetics, whereas basic and oxidative degradation reactions have first-order kinetics. The structural characterization of baloxavir marboxil degradation products was performed by coupling the optimized HPLC method to the triple-quadrupole tandem mass spectrometer. The proposed approach was validated according to the International Council for Harmonisation Q2 (R1) requirements for accuracy, precision, robustness, specificity, and linearity. The proposed approach was successfully used to analyze baloxavir marboxil as raw material and its pharmaceutical dosage form, Xofluza®. This article is protected by copyright. All rights reserved.

Antiviral Drugs in Influenza

Flu is a serious health, medical, and economic problem, but no therapy is yet available that has satisfactory results and reduces the occurrence of these problems. Nearly 20 years after the registration of the previous therapy, baloxavir marboxil, a drug with a new mechanism of action, recently appeared on the market. This is a promising step in the fight against the influenza virus. This article presents the possibilities of using all available antiviral drugs specific for influenza A and B. We compare all currently recommended anti-influenza medications, considering their mechanisms of action, administration, indications, target groups, effectiveness, and safety profiles. We demonstrate that baloxavir marboxil presents a similar safety and efficacy profile to those of drugs already used in the treatment of influenza. Further research on combination therapy is highly recommended and may have promising results.

Respiratory viral infections in the immunocompromised

PURPOSE OF REVIEW

During much of the COVID-19 pandemic, respiratory viruses other than SARS-CoV-2 did not infect immunocompromised patients. As mitigation strategies lighten, there has been a rapid resurgence of respiratory viruses globally. This review will summarize our current options for the management of the common respiratory viruses in transplant recipients.

RECENT FINDINGS

Expansion of the availability and increased utilization of multiplex molecular assays have allowed the recognition of the scope of respiratory virus infections in the transplant populations. New antivirals for influenza, respiratory syncytial virus (RSV), parainfluenza virus (PIV) and adenovirus show promise to improve outcomes of these important infections.

SUMMARY

Several new antiviral agents, including combination therapy of oseltamivir as well as baloxavir for influenza, fusion and nucleoprotein inhibitors for RSV, DAS181 for PIV and brincidofovir for adenovirus, hold promise to speed clearance of the virus, improve clinical outcomes and reduce the risk of resistance emergence.

Clinical effectiveness of baloxavir marboxil against influenza in three seasons

BACKGROUND

Previous reports have not clarified the difference in clinical efficacy between baloxavir and oseltamivir against influenza.

METHODS

A prospective observational study was performed during 2017-2018, 2018-2019, and 2019-2020 influenza seasons. The primary endpoint of this study was to compare the duration of fever between patients who received baloxavir and those who received oseltamivir.

RESULTS

A total of 235 influenza-infected patients (3-18 years of age), including 91 who received oseltamivir and 144 who received baloxavir, were enrolled. The proportions of influenza A(H3N2) virus, influenza A(H1N1)pdm09 virus, and influenza B virus-infected patients were 31.5%, 42.6%, and 26.0%, respectively. Patients who received oseltamivir were significantly younger than those who received baloxavir. Univariate analyses showed that the duration of fever was shorter with baloxavir than with oseltamivir against influenza virus overall, influenza A virus, influenza B virus, and influenza A(H1N1)pdm09 virus, but not for influenza A(H3N2) virus. In multivariate analyses, hazard ratios for influenza virus overall (0.53 [95% CI, 0.38-0.73]), influenza B virus (0.16 [95% CI, 0.07-0.41]), and influenza A(H1N1)pdm09 virus (0.55 [95% CI, 0.32-0.93]) were significantly lower in the patients who received baloxavir than those who received oseltamivir. However, the differences between influenza A virus and influenza A(H3N2) virus were not significant between the two groups.

CONCLUSION

For influenza virus overall, influenza B virus, and influenza A(H1N1)pdm09 virus, baloxavir treatment resulted in shorter duration of fever than oseltamivir treatment, but not for influenza A virus and influenza A(H3N2) virus.

Mesenchymal stem/stromal cell-based therapies for severe viral pneumonia: therapeutic potential and challenges

Severe viral pneumonia is a significant cause of morbidity and mortality globally, whether due to outbreaks of endemic viruses, periodic viral epidemics, or the rarer but devastating global viral pandemics. While limited anti-viral therapies exist, there is a paucity of direct therapies to directly attenuate viral pneumonia-induced lung injury, and management therefore remains largely supportive. Mesenchymal stromal/stem cells (MSCs) are receiving considerable attention as a cytotherapeutic for viral pneumonia. Several properties of MSCs position them as a promising therapeutic strategy for viral pneumonia-induced lung injury as demonstrated in pre-clinical studies in relevant models. More recently, early phase clinical studies have demonstrated a reassuring safety profile of these cells. These investigations have taken on an added importance and urgency during the COVID-19 pandemic, with multiple trials in progress across the globe. In parallel with clinical translation, strategies are being investigated to enhance the therapeutic potential of these cells in vivo, with different MSC tissue sources, specific cellular products including cell-free options, and strategies to ‘licence’ or ‘pre-activate’ these cells, all being explored. This review will assess the therapeutic potential of MSC-based therapies for severe viral pneumonia. It will describe the aetiology and epidemiology of severe viral pneumonia, describe current therapeutic approaches, and examine the data suggesting therapeutic potential of MSCs for severe viral pneumonia in pre-clinical and clinical studies. The challenges and opportunities for MSC-based therapies will then be considered.

Management of Severe Influenza

Influenza infection causes severe illness in 3 to 5 million people annually, with up to an estimated 650,000 deaths per annum. As such, it represents an ongoing burden to health care systems and human health. Severe acute respiratory infection can occur, resulting in respiratory failure requiring intensive care support. Herein we discuss diagnostic approaches, including development of CLIA-waived point of care tests that allow rapid diagnosis and treatment of influenza. Bacterial and fungal coinfections in severe influenza pneumonia are associated with worse outcomes, and we summarize the approach and treatment options for diagnosis and treatment of bacterial and Aspergillus coinfection. We discuss the available drug options for the treatment of severe influenza, and treatments which are no longer supported by the evidence base. Finally, we describe the supportive management and ventilatory approach to patients with respiratory failure as a result of severe influenza in the intensive care unit.

Antiviral Treatments for Influenza

Influenza is an acute respiratory illness caused by the influenza A, B, and C viruses. It can occur in local outbreaks or seasonal epidemics, with possibility to spread worldwide in a pandemic when a novel strain with significant antigenic differences emerges. During the past years, several new drugs have become available, with different accessibility related to specific countries' approval. We have conducted a review of literature, analyzing the most recent data on efficacy and safety of drugs currently available to treat influenza, with a particular attention toward special populations. Efficacy and safety profile of neuraminidase inhibitors (oseltamivir, zanamivir, laninamivir, peramivir) and recently approved cap-dependent endonuclease inhibitor baloxavir marboxil are reported in literature, but still little information is available about special populations such as critically ill patients and patients with a history of chronic respiratory disease. Moreover, the emergence of strains with reduced or no susceptibility to current drugs is a matter of concern, suggesting the need of constant monitoring of viral variants.

Influenza Management During the COVID-19 Pandemic: A Review of Recent Innovations in Antiviral Therapy and Relevance to Primary Care Practice

Seasonal influenza requires appropriate management to protect public health and resources. Decreasing the burden of influenza will depend primarily on increasing vaccination rates as well as prompt initiation of antiviral therapy within 48 hours of symptom onset, especially in the context of the current coronavirus disease 2019 pandemic. A careful approach is required to prevent health services from being overwhelmed by a surge in demand that could exceed capacity. This review highlights the societal burden of influenza and discusses the prevention, diagnosis, and treatment of influenza as a complicating addition to the challenges of the coronavirus disease 2019 pandemic. The importance of vaccination for seasonal influenza and the role of antiviral therapy in the treatment and prophylaxis of seasonal influenza, including the most up-to-date recommendations from the Centers for Disease Control and Prevention for influenza management, will also be reviewed.

Recommendations for Prevention and Control of Influenza in Children, 2021-2022

This technical report accompanies the recommendations of the American Academy of Pediatrics for the routine use of the influenza vaccine and antiviral medications in the prevention and treatment of influenza in children during the 2021-2022 season. Influenza vaccination is an important intervention to protect vulnerable populations and reduce the burden of respiratory illnesses during circulation of severe acute respiratory syndrome coronavirus 2, which is expected to continue during this influenza season. In this technical report, we summarize recent influenza seasons, morbidity and mortality in children, vaccine effectiveness, vaccination coverage, and detailed guidance on storage, administration, and implementation. We also provide background on inactivated and live attenuated influenza vaccine recommendations, vaccination during pregnancy and breastfeeding, diagnostic testing, and antiviral medications for treatment and chemoprophylaxis.

Clinical efficacy of antiviral agents against coronavirus disease 2019: A systematic review of randomized controlled trials

Despite aggressive efforts on containment measures for the coronavirus disease 2019 (COVID-19) pandemic around the world, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is continuously spreading. Therefore, there is an urgent need for an effective antiviral agent. To date, considerable research has been conducted to develop different approaches to COVID-19 therapy. In addition to early observational studies, which could be limited by study design, small sample size, non-randomized design, or different timings of treatment, an increasing number of randomized controlled trials (RCTs) investigating the clinical efficacy and safety of antiviral agents are being carried out. This study reviews the updated findings of RCTs regarding the clinical efficacy of eight antiviral agents against COVID-19, including remdesivir, lopinavir/ritonavir, favipiravir, sofosbuvir/daclatasvir, sofosbuvir/ledipasvir, baloxavir, umifenovir, darunavir/cobicistat, and their combinations. Treatment with remdesivir could accelerate clinical improvement; however, it lacked additional survival benefits. Moreover, 5-day regimen of remdesivir might show adequate effectiveness in patients with mild to moderate COVID-19. Favipiravir was only marginally effective regarding clinical improvement and virological assessment based on the results of small RCTs. The present evidence suggests that sofosbuvir/daclatasvir may improve survival and clinical outcomes in patients with COVID-19. However, the sample sizes for analysis were relatively small, and all studies were exclusively conducted in Iran. Further larger RCTs in other countries are warranted to support these findings. In contrast, the present findings of limited RCTs did not indicate the use of lopinavir/ritonavir, sofosbuvir/ledipasvir, baloxavir, umifenovir, and darunavir/cobicistat in the treatment of patients hospitalized for COVID-19.

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

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

Identification of Potential Drug Targets of Broad-Spectrum Inhibitors with a Michael Acceptor Moiety Using Shotgun Proteomics

The Michael addition reaction is a spontaneous and quick chemical reaction that is widely applied in various fields. This reaction is performed by conjugating an addition of nucleophiles with α, β-unsaturated carbonyl compounds, resulting in the bond formation of C-N, C-S, C-O, and so on. In the development of molecular materials, the Michael addition is not only used to synthesize chemical compounds but is also involved in the mechanism of drug action. Several covalent drugs that bond via Michael addition are regarded as anticarcinogens and anti-inflammatory drugs. Although drug development is mainly focused on pharmaceutical drug discovery, target-based discovery can provide a different perspective for drug usage. However, considerable time and labor are required to define a molecular target through molecular biological experiments. In this review, we systematically examine the chemical structures of current FDA-approved antiviral drugs for potential Michael addition moieties with α, β-unsaturated carbonyl groups, which may exert an unidentified broad-spectrum inhibitory mechanism to target viral or host factors. We thus propose that profiling the targets of antiviral agents, such as Michael addition products, can be achieved by employing a high-throughput LC-MS approach to comprehensively analyze the interaction between drugs and targets, and the subsequent drug responses in the cellular environment to facilitate drug repurposing and/or identify potential adverse effects, with a particular emphasis on the pros and cons of this shotgun proteomic approach.

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

Background

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

Methods

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

Discussion

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

Preparing for the 2020-2021 influenza season

The COVID-19 pandemic has altered health seeking behaviors and has increased attention to non-pharmaceutical interventions that reduce the risk of transmission of respiratory viruses including SARS-CoV-2 and influenza. While the potential impact of the COVID-19 pandemic on influenza is not fully known, in the Southern hemisphere influenza infection rates appear to be very low. Influenza vaccine efficacy for 2019-2020 season was comparable to prior season and influenza vaccine recommendations for pediatric immunizations remain similar to prior years. Influenza treatments continue to include neuraminidase inhibitors as well as baloxavir for treatment and in some instances prophylaxis.

Reducing influenza virus transmission: the value of antiviral treatment

Prompt antiviral treatment has the potential to reduce influenza virus transmission to close contacts, but rigorous data on the magnitude of treatment effects on transmission are limited. Animal model data indicate that rapid reductions in viral replication after antiviral treatment reduce the risk of transmission. Observational and clinical trial data with oseltamivir and other neuraminidase inhibitors indicate that prompt treatment of household index patients seems to reduce the risk of illness in contacts, although the magnitude of the reported effects has varied widely across studies. In addition, the potential risk of transmitting drug-resistant variants exists with all approved classes of influenza antivirals. A controlled trial examining baloxavir treatment efficacy to reduce transmission, including the risk of transmitting virus with reduced baloxavir susceptibility, is currently in progress. If reduced transmission risk is confirmed, modeling studies indicate that early treatment could have major epidemiologic benefits in seasonal and pandemic influenza.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

Evaluating the fitness of PA/I38T-substituted influenza A viruses with reduced baloxavir susceptibility in a competitive mixtures ferret model

Baloxavir is approved in several countries for the treatment of uncomplicated influenza in otherwise-healthy and high-risk patients. Treatment-emergent viruses with reduced susceptibility to baloxavir have been detected in clinical trials, but the likelihood of widespread occurrence depends on replication capacity and onward transmission. We evaluated the fitness of A/H3N2 and A/H1N1pdm09 viruses with the polymerase acidic (PA) I38T-variant conferring reduced susceptibility to baloxavir relative to wild-type (WT) viruses, using a competitive mixture ferret model, recombinant viruses and patient-derived virus isolates. The A/H3N2 PA/I38T virus showed a reduction in within-host fitness but comparable between-host fitness to the WT virus, while the A/H1N1pdm09 PA/I38T virus had broadly similar within-host fitness but substantially lower between-host fitness. Although PA/I38T viruses replicate and transmit between ferrets, our data suggest that viruses with this amino acid substitution have lower fitness relative to WT and this relative fitness cost was greater in A/H1N1pdm09 viruses than in A/H3N2 viruses.

Influenza viruses are associated with considerable disease burden and circulate annually causing seasonal epidemics. Antiviral drugs can be used to treat influenza infections and help reduce the disease burden. Occasionally, treatment can lead to the emergence of viruses with reduced antiviral susceptibility. Normally such viruses have reduced ‘fitness’, meaning they do not tend to spread or transmit widely, however on rare occasions, oseltamivir-resistant variants have become widespread in the community, thereby reducing the utility of the drug for treatment. Baloxavir is an antiviral recently licensed in many parts of the world for the treatment of influenza. Viruses with reduced susceptibility to baloxavir have been observed in clinical trials, but the frequency of such variants in the community has remained low (<0.1% globally since 2017–2018). We evaluated the fitness of viruses in ferrets and found that although A/H1N1 and A/H3N2 viruses with reduced baloxavir susceptibility were able to replicate and transmit among ferrets, they had a moderate reduction in fitness compared to normal ‘wild-type’ viruses, suggesting a reduced likelihood of spread. Surveillance to monitor for the frequency of viruses with reduced baloxavir susceptibility remains important.

Prophylaxis and treatment of influenza: options, antiviral susceptibility, and existing recommendations

Influenza viruses of types A and B attack 5-10% of adults and 20-30% of children, thereby causing millions of acute respiratory infections in Germany annually. A significant number of these infections are associated with complications such as pneumonia and bacterial superinfections that need hospitalization and might lead to death. In addition to vaccines, drugs were developed that might support influenza prevention and that can be used to treat influenza patients. The timely application of anti-influenza drugs can inhibit virus replication, help reduce and shorten the symptoms, and prevent death as well as virus transmission. This review concisely describes the mechanism of action, the potential for prophylactic and therapeutic use, and the knowledge on resistance of anti-influenza drugs approved today. However, the main aim is to give an overview on the recommendations available in Germany for the proper use of these drugs. In doing so, the recommendations published in statements and guidelines of medical societies as well as the German influenza pandemic preparedness plan are summarized with the consideration of specific circumstances and groups of patients.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Understanding the Impact of Resistance to Influenza Antivirals

Influenza poses a significant burden on society and health care systems. Although antivirals are an integral tool in effective influenza management, the potential for the emergence of antiviral-resistant viruses can lead to uncertainty and hesitation among front-line prescribers and policy makers. Here, we provide an overview of influenza antiviral resistance in context, exploring the key concepts underlying its development and clinical impact. Due to the acute nature of influenza in immunocompetent patients, resistant viruses that develop during antiviral treatment of a single patient ("treatment-emergent resistance") are usually cleared in a relatively short time, with no impact on future antiviral efficacy. In addition, although available data are limited by small numbers of patients, they show that antiviral treatment still provides clinical benefit to the patient within whom resistance emerges. In contrast, the sustained community transmission of resistant variants in the absence of treatment ("acquired resistance") is of greater concern and can potentially render front-line antivirals ineffective. Importantly, however, resistant viruses are usually associated with reduced fitness such that their widespread transmission is relatively rare. Influenza antivirals are an essential part of effective influenza management due to their ability to reduce the risk of complications and death in infected patients. Although antiviral resistance should be taken seriously and requires continuous careful monitoring, it is not comparable to antibiotic resistance in bacteria, which can become permanent and widespread, with far-reaching medical consequences. The benefits of antiviral treatment far outweigh concerns of potential resistance, which in the vast majority of cases does not have a significant clinical impact.

Interactions of Influenza and SARS-CoV-2 with the Lung Endothelium: Similarities, Differences, and Implications for Therapy

Respiratory viruses such as influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are a constant threat to public health given their ability to cause global pandemics. Infection with either virus may lead to aberrant host responses, such as excessive immune cell recruitment and activation, dysregulated inflammation, and coagulopathy. These may contribute to the development of lung edema and respiratory failure. An increasing amount of evidence suggests that lung endothelial cells play a critical role in the pathogenesis of both viruses. In this review, we discuss how infection with influenza or SARS-CoV-2 may induce endothelial dysfunction. We compare the effects of infection of these two viruses, how they may contribute to pathogenesis, and discuss the implications for potential treatment. Understanding the differences between the effects of these two viruses on lung endothelial cells will provide important insight to guide the development of therapeutics.

[Pharmacotherapy for acute respiratory infections caused by influenza viruses: current possibilities]

Routinely the influenza virus significantly contributes to the formation of the annual incidence of acute respiratory infections, with a peak in winter season. The high level of mutagenic potential of influenza viruses is a standard factor determining the complexity of the rational choice of pharmacotherapy. The upcoming epidemiological season 20202021 brings additional challenges for health care practitioners mediated by the widespread prevalence in the human population of a new infection caused by the SARS-CoV-2 virus affecting the respiratory system among many organs and systems. An adequate choice of pharmacotherapy tools should be based on high efficiency and safety of drugs, with a possible reduction in such negative factors as polypharmacy. This review includes comparative pharmacological characteristics of drugs with activity against RNA viruses, along with parameters of their clinical efficacy.