Oseltamivir-resistant pandemic (H1N1) 2009 virus infection in England and Scotland, 2009-2010

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.

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.

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.

In Vitro Characterization of Multidrug-Resistant Influenza A(H1N1)pdm09 Viruses Carrying a Dual Neuraminidase Mutation Isolated from Immunocompromised Patients

Influenza A(H1N1)pdm09 viruses carrying a dual neuraminidase (NA) substitution were isolated from immunocompromised patients after administration of one or more NA inhibitors. These mutant viruses possessed an H275Y/I223R, H275Y/I223K, or H275Y/G147R substitution in their NA and showed enhanced cross-resistance to oseltamivir and peramivir and reduced susceptibility to zanamivir compared to single H275Y mutant viruses. Baloxavir could be a treatment option against the multidrug-resistant viruses because these dual H275Y mutant viruses showed susceptibility to this drug. The G147R substitution appears to stabilize the NA structure, with the fitness of the H275Y/G147R mutant virus being similar or somewhat better than that of the wild-type virus. Since the multidrug-resistant viruses may be able to transmit between humans, surveillance of these viruses must continue to improve clinical management and to protect public health.

Neuraminidase inhibitors as a strategy for influenza treatment: pros, cons and future perspectives

Introduction: Influenza represents a major public health threat worldwide. Implementation of good personal health and hygiene habits, together with vaccination, is the most effective tools to reduce influenza burden both in community and in healthcare setting. However, achieving adequate vaccination rates is challenging, and vaccination does not always guarantee complete protection. Neuraminidase inhibitors represent an important measure to reduce the risk of influenza-related complications among high-risk patients developing influenza infection. Areas covered: Neuraminidase inhibitors have been proven to be safe and effective in reducing influenza severity, duration of symptoms, hospitalizations, and influenza-related-mortality. Here the authors review the available data on neuraminidase inhibitors, including the mechanism of action, pharmacokinetics, efficacy, safety and current indications for their use in clinical practice. Expert opinion: Although vaccination is the most effective tool to reduce influenza-associated morbidity and mortality, neuraminidase inhibitors represent an important option for the treatment of patients with influenza infection, particularly in high-risk categories. Moreover, antivirals play an important role in influenza prevention and prophylaxis in selected settings.

RNA respiratory viral infections in solid organ transplant recipients: Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

These updated guidelines from the Infectious Diseases Community of Practice of the American Society of Transplantation review the diagnosis, prevention, and management of RNA respiratory viral infections in the pre‐ and post‐transplant period. Viruses reviewed include influenza, respiratory syncytial virus (RSV), parainfluenza, rhinovirus, human metapneumovirus (hMPV), and coronavirus. Diagnosis is by nucleic acid testing due to improved sensitivity, specificity, broad range of detection of viral pathogens, automatization, and turnaround time. Respiratory viral infections may be associated with acute rejection and chronic lung allograft dysfunction in lung transplant recipients. The cornerstone of influenza prevention is annual vaccination and in some cases antiviral prophylaxis. Treatment with neuraminidase inhibitors and other antivirals is reviewed. Prevention of RSV is limited to prophylaxis with palivizumab in select children. Therapy of RSV upper or lower tract disease is controversial but may include oral or aerosolized ribavirin in some populations. There are no approved vaccines or licensed antivirals for parainfluenza, rhinovirus, hMPV, and coronavirus. Potential management strategies for these viruses are given. Future studies should include prospective trials using contemporary molecular diagnostics to understand the true epidemiology, clinical spectrum, and long‐term consequences of respiratory viruses as well as to define preventative and therapeutic measures.

Clinical Practice Guidelines by the Infectious Diseases Society of America: 2018 Update on Diagnosis, Treatment, Chemoprophylaxis, and Institutional Outbreak Management of Seasonal Influenzaa

These clinical practice guidelines are an update of the guidelines published by the Infectious Diseases Society of America (IDSA) in 2009, prior to the 2009 H1N1 influenza pandemic. This document addresses new information regarding diagnostic testing, treatment and chemoprophylaxis with antiviral medications, and issues related to institutional outbreak management for seasonal influenza. It is intended for use by primary care clinicians, obstetricians, emergency medicine providers, hospitalists, laboratorians, and infectious disease specialists, as well as other clinicians managing patients with suspected or laboratory-confirmed influenza. The guidelines consider the care of children and adults, including special populations such as pregnant and postpartum women and immunocompromised patients.

Clinical Practice Guidelines by the Infectious Diseases Society of America: 2018 Update on Diagnosis, Treatment, Chemoprophylaxis, and Institutional Outbreak Management of Seasonal Influenzaa

These clinical practice guidelines are an update of the guidelines published by the Infectious Diseases Society of America (IDSA) in 2009, prior to the 2009 H1N1 influenza pandemic. This document addresses new information regarding diagnostic testing, treatment and chemoprophylaxis with antiviral medications, and issues related to institutional outbreak management for seasonal influenza. It is intended for use by primary care clinicians, obstetricians, emergency medicine providers, hospitalists, laboratorians, and infectious disease specialists, as well as other clinicians managing patients with suspected or laboratory-confirmed influenza. The guidelines consider the care of children and adults, including special populations such as pregnant and postpartum women and immunocompromised patients.

Safety and effectiveness of neuraminidase inhibitors in situations of pandemic and/or novel/variant influenza: a systematic review of the literature, 2009-15

Objectives

To review systematically the published literature evaluating neuraminidase inhibitor (NI) safety and effectiveness in situations of pandemic and novel/variant influenza.

Methods

We searched six online databases using comprehensive search criteria for observational studies and randomized controlled trials investigating the effects of NI treatment, prophylaxis or outbreak control in patients of all ages.

Results

Overall, 165 studies were included (95% observational), which were generally of low methodological quality due to lack of adjustment for confounding variables. In studies reporting adjusted estimates in general populations, NI treatment appeared likely to be effective against mortality (primarily if administered within 48 h of symptom onset) and potentially effective in reducing pneumonia. NIs appeared effective in reducing secondary transmission when indicated for prophylaxis. Limited, low-quality data suggest NIs are likely safe in general populations and may be safe in pregnant women and children. Data are scarce regarding safety of NIs in adults and high-risk individuals.

Conclusions

Most included studies were observational, statistically underpowered and at high risk of reporting biased and/or confounded effect estimates. NI treatment appeared likely effective in reducing mortality (cause unspecified) and pneumonia in general populations, with increasing benefit when administered with 48 h of symptom onset. NI pre- or post-exposure prophylaxis is likely effective in reducing secondary transmission of influenza in a general population. Our evidence suggests NIs are likely safe to use in the general population; however, data for children and pregnant women are limited. Knowledge gaps persist in specific populations such as Aboriginals, high-risk individuals and the elderly.

Clinical Implications of Antiviral Resistance in Influenza

Influenza is a major cause of severe respiratory infections leading to excessive hospitalizations and deaths globally; annual epidemics, pandemics, and sporadic/endemic avian virus infections occur as a result of rapid, continuous evolution of influenza viruses. Emergence of antiviral resistance is of great clinical and public health concern. Currently available antiviral treatments include four neuraminidase inhibitors (oseltamivir, zanamivir, peramivir, laninamivir), M2-inibitors (amantadine, rimantadine), and a polymerase inhibitor (favipiravir). In this review, we focus on resistance issues related to the use of neuraminidase inhibitors (NAIs). Data on primary resistance, as well as secondary resistance related to NAI exposure will be presented. Their clinical implications, detection, and novel therapeutic options undergoing clinical trials are discussed.

Synthesis and antiviral activity of some novel indole-2-carboxylate derivatives

A series of novel indole-2-carboxylate derivatives were synthesized and assayed to determine their in vitro broad-spectrum antiviral activities. The biological results showed that some of the synthesized compounds exhibited potent broad-spectrum antiviral activity. Notably, compound 8f showed the highest SI value (17.1) to Cox B3 virus. Compound 14f showed both potent inhibitory activity against influenza A (IC50=7.53 μmol/L) and the highest SI value (12.1). SAR results showed that the alkyloxy at the 4-position of indole ring was not crucial to the antiviral activities. Incorporation of an acetyl substituent at the amino group disfavored antiviral activity towards RNA viruses.

Prolonged shedding of pandemic influenza A (H1N1) 2009 virus in a pancreas-after-kidney transplant recipient

Prolonged shedding of influenza virus has been reported in immunocompromised patients. Delayed viral clearance may contribute to antiviral resistance and nosocomial transmission. We report a case of a pancreas-after-kidney transplant recipient who had detectable pandemic influenza A virus for 12 months. Pyrosequencing analysis detected the H275Y mutation, which is associated with resistance to oseltamivir.

A zanamivir dimer with prophylactic and enhanced therapeutic activity against influenza viruses

OBJECTIVES

Emerging drug resistance to antiviral therapies is an increasing challenge for the treatment of influenza virus infections. One new antiviral compound, BTA938, a dimeric derivative of the viral neuraminidase inhibitor zanamivir, contains a 14-carbon linker bridging two zanamivir moieties. In these studies, we evaluated antiviral efficacy in cell cultures infected with influenza virus and in mouse models of lethal influenza using H1N1pdm09, H3N2 and oseltamivir-resistant (H275Y) viruses.

METHODS

In vitro activity was evaluated against 22 strains of influenza virus. Additionally, in vivo studies compared the efficacy of BTA938 or zanamivir after intranasal treatment. We also tested the hypothesis of a dual mode of action for BTA938 using scanning electron microscopy (SEM).

RESULTS

BTA938 inhibited the viruses at nanomolar concentrations in vitro with a median 50% effective concentration value of 0.5 nM. In mouse models, the dimer provided ∼10-fold greater protection than zanamivir. The data also showed that a single low dose (3 mg/kg) protected 100% of mice from an otherwise lethal oseltamivir-resistant (H275Y) influenza virus infection. Remarkably, a single prophylactic treatment (10 mg/kg) administered 7 days before the challenge protected 70% of mice and when administered 1 or 3 days before the challenge it protected 90% of mice. Additionally, SEM provides evidence that the increased antiviral potency may be mediated by an enhanced aggregation of virus on the cell surface.

CONCLUSIONS

In vitro and in vivo experiments showed the high antiviral activity of BTA938 for the treatment of influenza virus infections. Moreover, we demonstrated that a single dose of BTA938 is sufficient for prophylactic and therapeutic protection in mouse models.

Access to the NHS by telephone and Internet during an influenza pandemic: an observational study

OBJECTIVES

To examine use of a novel telephone and Internet service-the National Pandemic Flu Service (NPFS)-by the population of England during the 2009-2010 influenza pandemic.

SETTING

National telephone and Internet-based service.

PARTICIPANTS

Service available to population of England (n=51.8 million).

PRIMARY AND SECONDARY OUTCOME MEASURES

Primary: service use rate, by week. Numbers and age-specific and sex-specific rates of population who: accessed service; were authorised to collect antiviral medication; collected antiviral medication; were advised to seek further face-to-face assessment. Secondary: daily mean contacts by hour; proportion using service by telephone/Internet.

RESULTS

The NPFS was activated on 23 July 2009, operated for 204 days and assessed 2.7 million patients (5200 consultations/100 000 population). This was six times the number of people who consulted their general practitioner with influenza-like illness during the same period (823 consultations/100 000 population, rate ratio (RR)=6.30, 95% CI 6.28 to 6.32). Women used the service more than men (52.6 vs 43.4 assessments/1000 population, RR1 21, 95% CI 1.21 to 1.22). Among adults, use of the service declined with age (16-29 years: 74.4 vs 65 years+: 9.9 assessments/1000 population (RR 7.46 95% CI 7.41 to 7.52). Almost three-quarters of those assessed met the criteria to receive antiviral medication (1 807 866/2 488 510; 72.6%). Most of the people subsequently collected this medication, although more than one-third did not (n=646 709; 35.8%). Just over one-third of those assessed were advised to seek further face-to-face assessment with a practitioner (951 332/2 488 504; 38.2%).

CONCLUSIONS

This innovative healthcare service operated at large scale and achieved its aim of relieving considerable pressure from mainstream health services, while providing appropriate initial assessment and management for patients. This offers proof-of-concept for such a service that, with further refinement, England can use in future pandemics. Other countries may wish to adopt a similar system as part of their pandemic emergency planning.

Tracking oseltamivir-resistance in New Zealand influenza viruses during a medicine reclassification in 2007, a resistant-virus importation in 2008 and the 2009 pandemic

INTRODUCTION

Oseltamivir (Tamiflu®) is an important pharmaceutical intervention against the influenza virus. The importance of surveillance for resistance to oseltamivir has been highlighted by two global events: the emergence of an oseltamivir-resistant seasonal influenza A(H1N1) virus in 2008, and emergence of the influenza A(H1N1)pdm09 virus in 2009. Oseltamivir is a prescription medicine in New Zealand, but more timely access has been provided since 2007 by allowing pharmacies to directly dispense oseltamivir to patients with influenza-like illness.

OBJECTIVE

To determine the frequency of oseltamivir-resistance in the context of a medicine reclassification in 2007, the importation of an oseltamivir-resistant seasonal influenza virus in 2008, and the emergence of a pandemic in 2009.

METHODS

A total of 1795 influenza viruses were tested for oseltamivir-resistance using a fluorometric neuraminidase inhibition assay. Viruses were collected as part of a sentinel influenza surveillance programme between the years 2006 and 2010.

RESULTS

All influenza B, influenza A(H3N2) and influenza A(H1N1)pdm09 viruses tested between 2006 and 2010 were shown to be sensitive to oseltamivir. Seasonal influenza A(H1N1) viruses from 2008 and 2009 were resistant to oseltamivir. Sequencing of the neuraminidase gene showed that the resistant viruses contained an H275Y mutation, and S247N was also identified in the neuraminidase gene of one seasonal influenza A(H1N1) virus that exhibited enhanced resistance.

DISCUSSION

No evidence was found to suggest that increased access to oseltamivir has promoted resistance. A probable importation event was documented for the global 2008 oseltamivir-resistant seasonal A(H1N1) virus nine months after it was first reported in Europe in January 2008.

Model-based simulation and prediction of an antiviral strategy against influenza A infection

There is a strong need to develop novel strategies in using antiviral agents to efficiently treat influenza infections. Thus, we constructed a rule-based mathematical model that reflects the complicated interactions of the host immunity and viral life cycle and analyzed the key controlling steps of influenza infections. The main characteristics of the pandemic and seasonal influenza strains were estimated using parameter values derived from cells infected with Influenza A/California/04/2009 and Influenza A/NewCaledonia/20/99, respectively. The quantitative dynamics of the infected host cells revealed a more aggressive progression of the pandemic strain than the seasonal strain. The perturbation of each parameter in the model was then tested for its effects on viral production. In both the seasonal and pandemic strains, the inhibition of the viral release (k_C), the reinforcement of viral attachment (k_V), and an increased transition rate of infected cells into activated cells (k_I) exhibited significant suppression effects on the viral production; however, these inhibitory effects were only observed when the numerical perturbations were performed at the early stages of the infection. In contrast, combinatorial perturbations of both the inhibition of viral release and either the reinforcement of the activation of infected cells or the viral attachment exhibited a significant reduction in the viral production even at a later stage of infection. These results suggest that, in addition to blocking the viral release, a combination therapy that also enhances either the viral attachment or the transition of the infected cells might provide an alternative for effectively controlling progressed influenza infection.

Virological self-sampling to monitor influenza antiviral susceptibility in a community cohort

Objective

To perform antiviral susceptibility monitoring of treated individuals in the community during the 2009 influenza A(H1N1) pandemic in England.

Patients and methods

Between 200 and 400 patients were enrolled daily through the National Pandemic Flu Service (NPFS) and issued with a self-sampling kit. Initially, only persons aged 16 and over were eligible, but from 12 November (week 45), self-sampling was extended to include school-age children (5 years and older). All samples received were screened for influenza A(H1N1)pdm09 as well as seasonal influenza [A(H1N1), A(H3N2) and influenza B] by a combination of RT–PCR and virus isolation methods. Influenza A(H1N1)pdm09 RT–PCR-positive samples were screened for the oseltamivir resistance-inducing H275Y substitution, and a subset of samples also underwent phenotypic antiviral susceptibility testing by enzyme inhibition assay.

Results

We were able to detect virus by RT–PCR in self-taken samples and recovered infectious virus enabling further virological characterization. The majority of influenza A(H1N1)pdm09 RT–PCR-positive NPFS samples (n = 1273) were taken after oseltamivir treatment had begun. No reduction in phenotypic susceptibility to neuraminidase inhibitors was detected, but five cases with minority quasi-species of oseltamivir-resistant virus (an H275Y amino acid substitution in neuraminidase) were detected.

Conclusions

Self-sampling is a useful tool for community surveillance, particularly for the follow-up of drug-treated patients. The virological study of self-taken samples from the NPFS provided a unique opportunity to evaluate the emergence of oseltamivir resistance in treated individuals with mild illness in the community, a target population that may not be captured by traditional sentinel surveillance schemes.

Synthesis and anti-influenza virus activities of a novel class of gastrodin derivatives

A series of substituted aryl glycoside analogues of gastrodin have been identified as potential anti-influenza agents. The most potent inhibitor 1a exhibited moderate inhibitory activity against the A/Hanfang/359/95(H3N2) and A/FM/1/47(H1N1) strains of the influenza A virus (IC(50) values of 44.40 and 34.45 μM, respectively) and the oseltamivir-null B/Jifang/13/97 strain of influenza B (IC(50) value of 33.01 μM). In this article, multiple doses of compound 1a (80 mg/kg/day, oral administration) were used for the treatment of mice infected with influenza A/FM/1/47-MA (H1N1), and surprisingly we found that compound 1a significantly increased the number of survivors and prolonged the mean survival time. The preliminary studies on the mechanism of antiviral activity showed no interaction between compound 1a and the neuraminidase or the M2 protein. The novel target to overcome drug resistance combined with its good in vivo profile support compound 1a to be a new lead for further development of antiviral agents.

Evaluation of influenza virus antiviral susceptibility testing in Europe: results from the first external quality assessment exercise

BACKGROUND

The first antiviral susceptibility testing external quality assessment (EQA) was held for European influenza reference laboratories during winter 2010/11.

OBJECTIVES

To assess European network influenza antiviral susceptibility testing capability and provide participants with an independent performance evaluation.

STUDY DESIGN

The EQA panel contained ten coded specimens of inactivated human influenza A and B viruses with reduced susceptibility to neuraminidase inhibitors (NAI), or adamantanes. Twenty-four laboratories from 19 member states of the WHO European region analysed the panel using phenotypic (determination of 50% inhibitory concentration (IC(50)) values by neuraminidase (NA) enzyme inhibition assay) and/or genotypic methods.

RESULTS

All 24 laboratories returned genotypic data for A(H1N1)pdm09 influenza virus, 18 (75%) for former seasonal A(H1N1), 16 (67%) for A(H3N2) and 15 (63%) for influenza B virus, correctly identifying NAI or adamantane reduced susceptibility-associated substitutions in the NA (mean 84%; range 52-100%) or M2 (mean 85%; range 73-94%), respectively. Thirteen laboratories (54%) returned phenotypic NAI susceptibility data. Despite inter-laboratory and inter-assay IC(50) value variation, all 13 laboratories correctly identified oseltamivir reduced susceptibility/resistance in pure preparations of A(H1N1) oseltamivir-resistant viruses. However, only 11 (85%) identified oseltamivir reduced susceptibility/resistance in a mixture of A(H1N1)pdm09 oseltamivir-sensitive/-resistant viruses. Furthermore, 3 laboratories (23%) considered oseltamivir-sensitive influenza B virus reduced susceptible/resistant.

CONCLUSIONS

Detection of NA-H275Y in A(H1N1) viruses was achieved by most laboratories. IC(50) values and interpretation thereof varied for a sensitive/resistant virus mixture and for influenza B virus. The results of this exercise will assist harmonisation of antiviral susceptibility testing, interpretation and reporting within the European network through targeted training.

Comparable fitness and transmissibility between oseltamivir-resistant pandemic 2009 and seasonal H1N1 influenza viruses with the H275Y neuraminidase mutation

Limited antiviral compounds are available for the control of influenza, and the emergence of resistant variants would further narrow the options for defense. The H275Y neuraminidase (NA) mutation, which confers resistance to oseltamivir carboxylate, has been identified among the seasonal H1N1 and 2009 pandemic influenza viruses; however, those H275Y resistant variants demonstrated distinct epidemiological outcomes in humans. Specifically, dominance of the H275Y variant over the oseltamivir-sensitive viruses was only reported for a seasonal H1N1 variant during 2008-2009. Here, we systematically analyze the effect of the H275Y NA mutation on viral fitness and transmissibility of A(H1N1)pdm09 and seasonal H1N1 influenza viruses. The NA genes from A(H1N1)pdm09 A/California/04/09 (CA04), seasonal H1N1 A/New Caledonia/20/1999 (NewCal), and A/Brisbane/59/2007 (Brisbane) were individually introduced into the genetic background of CA04. The H275Y mutation led to reduced NA enzyme activity, an increased K(m) for 3'-sialylactose or 6'-sialylactose, and decreased infectivity in mucin-secreting human airway epithelial cells compared to the oseltamivir-sensitive wild-type counterparts. Attenuated pathogenicity in both RG-CA04(NA-H275Y) and RG-CA04 × Brisbane(NA-H275Y) viruses was observed in ferrets compared to RG-CA04 virus, although the transmissibility was minimally affected. In parallel experiments using recombinant Brisbane viruses differing by hemagglutinin and NA, comparable direct contact and respiratory droplet transmissibilities were observed among RG-NewCal(HA,NA), RG-NewCal(HA,NA-H275Y), RG-Brisbane(HA,NA-H275Y), and RG-NewCal(HA) × Brisbane(NA-H275Y) viruses. Our results demonstrate that, despite the H275Y mutation leading to a minor reduction in viral fitness, the transmission potentials of three different antigenic strains carrying this mutation were comparable in the naïve ferret model.

Oseltamivir-resistant pandemic (H1N1) 2009 virus infections, United States, 2010-11

During October 2010–July 2011, 1.0% of pandemic (H1N1) 2009 viruses in the United States were oseltamivir resistant, compared with 0.5% during the 2009–10 influenza season. Of resistant viruses from 2010–11 and 2009–10, 26% and 89%, respectively, were from persons exposed to oseltamivir before specimen collection. Findings suggest limited community transmission of oseltamivir-resistant virus.

The yin and yang of viruses and interferons

Interferons (IFNs)-α/β are critical effectors of the innate immune response to virus infections. Through activation of the IFN-α/β receptor (IFNAR), they induce expression of IFN-stimulated genes (ISGs) that encode antiviral proteins capable of suppressing viral replication and promoting viral clearance. Many highly pathogenic viruses have evolved mechanisms to evade an IFN response and the balance between the robustness of the host immune response and viral antagonistic mechanisms determines whether or not the virus is cleared. Here, we discuss IFNs as broad-spectrum antivirals for treatment of acute virus infections. In particular, they are useful for treatment of re-emerging virus infections, where direct-acting antivirals (DAAs) have limited utility due to DAA-resistant mutations, and for newly emerging virus strains in which the time to vaccine availability precludes vaccination at the onset of an outbreak.

Neuraminidase H275Y and hemagglutinin D222G mutations in a fatal case of 2009 pandemic influenza A (H1N1) virus infection

Oseltamivir-resistant 2009 H1N1 influenza virus infections associated with neuraminidase (NA) H275Y have been identified sporadically. Strains possessing the hemagglutinin (HA) D222G mutation have been detected in small numbers of fatal 2009 H1N1 cases. We report the first clinical description of 2009 H1N1 virus infection with both NA-H275Y and HA-D222G mutations detected by pyrosequencing of bronchioalveolar lavage fluid obtained on symptom day 19. The 59-year-old immunosuppressed patient had multiple conditions conferring higher risk of prolonged viral replication and severe illness and died on symptom day 34. Further investigations are needed to determine the significance of infection with strains possessing NA-H275Y and HA-D222G.