Prophylaxis Of Influenza Research Articles

Competitive Fitness of Influenza B Viruses Possessing E119A and H274Y Neuraminidase Inhibitor Resistance-Associated Substitutions in Ferrets.

Neuraminidase (NA) inhibitors (NAIs) are the only antiviral drugs recommended for influenza treatment and prophylaxis. Although NAI-resistant influenza B viruses that could pose a threat to public health have been reported in the field, their fitness is poorly understood. We evaluated in ferrets the pathogenicity and relative fitness of reverse genetics (rg)–generated influenza B/Yamanashi/166/1998-like viruses containing E119A or H274Y NA substitutions (N2 numbering). Ferrets inoculated with NAI-susceptible rg–wild-type (rg-WT) or NAI-resistant (rg-E119A or rg-H274Y) viruses developed mild infections. Growth of rg-E119A virus in the nasal cavities was delayed, but the high titers at 3 days post-inoculation (dpi) were comparable to those of the rg-WT and rg-H274Y viruses (3.6–4.1 log10TCID50/mL). No virus persisted beyond 5 dpi and replication did not extend to the trachea or lungs. Positive virus antigen-staining of the nasal turbinate epithelium was intermittent with the rg-WT and rg-H274Y viruses; whereas antigen-staining for the rg-E119A virus was more diffuse. Virus populations in ferrets coinoculated with NAI-susceptible and -resistant viruses (1:1 mixture) remained heterogeneous at 5 dpi but were predominantly rg-WT (>70%). Although the E119A substitution was associated with delayed replication in ferrets, the H274Y substitution did not measurably affect viral growth properties. These data suggest that rg-H274Y has undiminished fitness in single virus inoculations, but neither rg-E119A nor rg-H274Y gained a fitness advantage over rg-WT in direct competition experiments without antiviral drug pressure. Taken together, our data suggest the following order of relative fitness in a ferret animal model: rg-WT > rg-H274Y > rg-E119A.

Detection of H275Y Mutation of A(H1N1)pdmO9 Viruses Using a Real-time RT-PCR Assay in Mongolia

Objectives: Oseltamivir is recommended as a first-line drug for the prophylaxis and treatment of influenza A(H1N1)pdmO9 infection worldwide. However, oseltamivir-resistant influenza A(H1N1)pdmO9 viruses have been identified and are mostly associated with an H275Y substitution in the neuraminidase (NA) gene. Careful and rapid laboratory testing for antiviral resistance surveillance of influenza viruses are important to public health and clinical sectors. The aim of our study was to determine oseltamivir-resistant H275Y mutation in clinical specimens by the real-time reverse transcriptase polymerase chain reaction (rtRT-PCR) assay in Mongolia. Methods: A total of 215 clinical specimens tested positive for the A(H1N1)pdmO9 influenza virus by rtRT-PCR. The specimens were collected between January 2013 and August 2014 from patients who visited influenza surveillance sites. All collected specimens were tested for the presence of the oseltamivir-resistant H275Y mutation by rtRT-PCR and DNA sequencing on the NA gene was performed on four of the clinical samples. Results: For all specimens, the H275 (Ct value = 20.4-34.5) was sensitive to oseltamivir by rtRT-PCR assay for detection of the H275Y mutations in the NA gene. Four questionable clinical samples were sequenced for the full NA gene. The data of these samples are available in GISAID influenza virus database with accession numbers EPI533542, EPI462274, EPI462271 and EPI460844. Conclusion: The A(H1 N1)pdm09 viruses were susceptible to oseltamivir during the study period in Mongolia. The rtRT-PCR assay is useful for detection of the H275Y substitution but other possible mutations in the NA gene of the virus could limit the utility of this technique.

Long-acting Neuraminidase Inhibitor Laninamivir Octanoate as Post-exposure Prophylaxis for Influenza.

A single administration of laninamivir octanoate, a long-acting neuraminidase inhibitor, has been proven to be effective in the treatment of influenza but not for post-exposure prophylaxis. We conducted a double-blind, multicenter, randomized, placebo-controlled study to determine if a single administration of laninamivir octanoate 40 mg was superior to placebo for post-exposure prophylaxis. Eligible participants who had cohabited with an influenza patient within 48 hours of symptom onset were randomly assigned (1:1:1) to 1 of 3 groups: 40 mg of laninamivir octanoate single administration (LO-40SD), 20 mg of laninamivir octanoate once daily for 2 days (LO-20TD), or placebo. The primary efficacy endpoint was the proportion of participants who developed clinical influenza (defined as influenza virus positive, an axillary temperature >37.5°C, and at least 2 symptoms) over a 10-day period. A total of 803 participants were enrolled, with 801 included in the primary analysis. The proportions of participants with clinical influenza were 4.5% (12/267), 4.5% (13/269), and 12.1% (32/265) in the LO-40SD, LO-20TD, and placebo groups, respectively. A single administration of laninamivir octanoate 40 mg significantly reduced the development of influenza compared with placebo (P = .001). The relative risk reductions compared with the placebo group were 62.8% and 63.1% for the LO-40SD and LO-20TD groups, respectively. The incidence of adverse events in the LO-40SD group was similar to that of the LO-20TD and placebo groups. A single administration of laninamivir octanoate was effective and well tolerated as post-exposure prophylaxis to prevent the development of influenza. JapicCTI-142679.

Globular Head-Displayed Conserved Influenza H1 Hemagglutinin Stalk Epitopes Confer Protection against Heterologous H1N1 Virus.

Significant genetic variability in the head region of the influenza A hemagglutinin, the main target of current vaccines, makes it challenging to develop a long-lived seasonal influenza prophylaxis. Vaccines based on the conserved hemagglutinin stalk domain might provide broader cross-reactive immunity. However, this region of the hemagglutinin is immunosubdominant to the head region. Peptide-based vaccines have gained much interest as they allow the immune system to focus on relevant but less immunogenic epitopes. We developed a novel influenza A hemagglutinin-based display platform for H1 hemagglutinin stalk peptides that we identified in an epitope mapping assay using human immune sera and synthetic HA peptides. Flow cytometry and competition assays suggest that the identified stalk sequences do not recapitulate the epitopes of already described broadly neutralizing stalk antibodies. Vaccine constructs displaying 25-mer stalk sequences provided up to 75% protection from lethal heterologous virus challenge in BALB/c mice and induced antibody responses against the H1 hemagglutinin. The developed platform based on a vaccine antigen has the potential to be either used as stand-alone or as prime-vaccine in combination with conventional seasonal or pandemic vaccines for the amplification of stalk-based cross-reactive immunity in humans or as platform to evaluate the relevance of viral peptides/epitopes for protection against influenza virus infection.

Update on influenza antiviral drug treatment and prophylaxis for the 2015–2016 influenza season

Update on influenza antiviral drug treatment and prophylaxis for the 2015–2016 influenza season

The C-Terminal Tail of TRIM56 Dictates Antiviral Restriction of Influenza A and B Viruses by Impeding Viral RNA Synthesis.

Accumulating data suggest that tripartite-motif-containing (TRIM) proteins participate in host responses to viral infections, either by acting as direct antiviral restriction factors or through regulating innate immune signaling of the host. Of >70 TRIMs, TRIM56 is a restriction factor of several positive-strand RNA viruses, including three members of the family Flaviviridae(yellow fever virus, dengue virus, and bovine viral diarrhea virus) and a human coronavirus (OC43), and this ability invariably depends upon the E3 ligase activity of TRIM56. However, the impact of TRIM56 on negative-strand RNA viruses remains unclear. Here, we show that TRIM56 puts a check on replication of influenza A and B viruses in cell culture but does not inhibit Sendai virus or human metapneumovirus, two paramyxoviruses. Interestingly, the anti-influenza virus activity was independent of the E3 ligase activity, B-box, or coiled-coil domain. Rather, deletion of a 63-residue-long C-terminal-tail portion of TRIM56 abrogated the antiviral function. Moreover, expression of this short C-terminal segment curtailed the replication of influenza viruses as effectively as that of full-length TRIM56. Mechanistically, TRIM56 was found to specifically impede intracellular influenza virus RNA synthesis. Together, these data reveal a novel antiviral activity of TRIM56 against influenza A and B viruses and provide insights into the mechanism by which TRIM56 restricts these medically important orthomyxoviruses. Options to treat influenza are limited, and drug-resistant influenza virus strains can emerge through minor genetic changes. Understanding novel virus-host interactions that alter influenza virus fitness may reveal new targets/approaches for therapeutic interventions. We show here that TRIM56, a tripartite-motif protein, is an intrinsic host restriction factor of influenza A and B viruses. Unlike its antiviral actions against positive-strand RNA viruses, the anti-influenza virus activity of TRIM56 was independent of the E3 ligase activity. Rather, expression of a short segment within the very C-terminal tail of TRIM56 inhibited the replication of influenza viruses as effectively as that of full-length TRIM56 by specifically targeting viral RNA synthesis. These data reveal the remarkable multifaceted activity of TRIM56, which has developed multiple domains to inhibit multiple viral families. They also raise the possibility of developing a broad-spectrum, TRIM56-based antiviral approach for addition to influenza prophylaxis and/or control strategies.

Problems of vaccine prophylaxis of influenza in pregnant women

Pregnant women are at high risk for the adverse course of respiratory diseases, among which the influenza is the one of the leading infections, of ten finishing tragically for most pregnant and her offspring. Due to the disproportionately high morbidity, mortality and adverse outcomes of pregnancy after influenza virus infection, pregnant females are classified as a priority group for vaccination. Immunization with inactivated influenza vaccine is one of the most important strategy to prevent both of influenza infection, its severe complications, and mitigating of the effects of the epidemic of influenza. There was accumulated sufficient evidence demonstrating that the vaccine promotes the diminution of clinical manifestations of influenza infection in pregnant women, as well, has a positive effect on the health of the newborns due to the active transport of maternal antibodies. In the review there are presented data on the safety, high immunogenicity and clinical efficacy of vaccination against influenza as for pregnant women as well for infants.

Effectiveness of Influenza Vaccine in Adults Using A Test-negative, Case-control Design ―2013/2014 and 2014/2015 Seasons―

The influenza vaccine forms the basis of efforts to prevent the occurrence of influenza virus infection. However, vaccine effectiveness (VE) differs every season, which complicates efforts to combat the spread of infection. To develop a robust method to analyse variations in VE, we assessed VE among adult patients with influenza using a test-negative, case-control study design that evaluated vaccination records and the corresponding results of rapid influenza diagnostic tests during the 2013/14 and 2014/15 influenza seasons. During the 2013/14season, the adjusted VEs against influenza A and B viruses were 54.9% (95% confidence interval [CI] = 24.2% - 73.2%) and 56.6% (95% CI = 19.1% - 76.7%), respectively. In contrast, during the 2014/15season, the adjusted VE against the influenza A (H3N2), virus was -2% (95% CI = -66% - 37.5%). Moreover, only a few patients were infected with the influenza B virus, thus, the VE against influenza B could not be assessed. The low VE during the 2014/15 season could be attributed to antigenic drift in the circulating influenza A (H3N2) viruses and mutations in the egg-adapted vaccine strains. Estimation of the VE against the influenza virus using this test-negative, case-control study design was simple and easy, and this study design had a precision similar to that of a randomized control trial. Therefore, this study design could be employed to predict VE through out the influenza season and may be used as the basis of influenza prophylaxis.

Use of neuraminidase inhibitors for prophylaxis and treatment of pandemic influenza: summary of a Faculty of Public Health meeting.

Use of neuraminidase inhibitors for prophylaxis and treatment of pandemic influenza: summary of a Faculty of Public Health meeting.

Prevalence of Influenza A(H1N1)pdm09 Virus Resistant to Oseltamivir in Shiraz, Iran, During 2012 - 2013.

Background:Oseltamivir has been used as a drug of choice for the prophylaxis and treatment of human influenza A(H1N1)pdm09 infection across the world. However, the most frequently identified oseltamivir resistant virus, influenza A(H1N1)pdm09, exhibit the H275Y substitution in NA gene.Objectives:This study aimed to determine the prevalence and phylogenetic relationships of oseltamivir resistance in influenza A(H1N1)pdm09 viruses isolated in Shiraz, Iran.Patients and Methods:Throat swab samples were collected from 200 patients with influenza-like disease from December 2012 until February 2013. A total of 77 influenza A(H1N1)pdm09 positive strains were identified by real-time polymerase chain reaction (PCR). Oseltamivir resistance was detected using quantal assay and nested-PCR method. The NA gene sequencing was conducted to detect oseltamivir-resistant mutants and establish the phylogeny of the prevalent influenza variants.Results:Our results revealed that A(H1N1)pdm09 viruses present in these samples were susceptible to oseltamivir, and contained 5 site specific mutations (V13G, V106I, V241I, N248D, and N369K) in NA gene. These mutations correlated with increasing expression and enzymatic activity of NA protein in the influenza A(H1N1)pdm09 viruses, which were closely related to a main influenza A(H1N1)pdm09 cluster isolated around the world.Conclusions:A(H1N1)pdm09 viruses, identified in this study in Shiraz, Iran, contained 5 site specific mutations and were susceptible to oseltamivir.

Use of embryonated chicken egg as a model to study the susceptibility of avian influenza H9N2 viruses to oseltamivir carboxylate

Avian influenza (AI) H9N2 viruses are endemic in many bird species, and human infections of H9N2 viruses have been reported. Oseltamivir phosphate (Tamiflu®) is the available antiviral drug for the treatment and prophylaxis of influenza. There are no reports of use of embryonated chicken egg as a model to study susceptibility of AI viruses to oseltamivir carboxylate (OC), the active metabolite. The present study was undertaken to explore the use of embryonated chicken eggs as a model for testing OC against the AI H9N2 viruses. A total of three AI H9N2 viruses, isolated in poultry in India, were used. Various virus dilutions were tested against 14μg/ml of OC. Three methods, namely (1) the in vitro virus–drug treatment, (2) drug delivery and virus challenge by allantoic route, and (3) drug delivery by albumen route and virus challenge by allantoic route were explored. The viruses were also tested using the fluorescence-based neuraminidase inhibitor (NAI) assay. There was significant inhibition (p<0.05) of the H9N2 viruses in presence of OC. The infectious virus titers as well as hemagglutination titers were significantly lower in presence of OC as compared to controls. The in vitro treatment of virus and drug; and drug and virus delivery at the same time by allantoic route showed significantly higher inhibition (p<0.05) of virus growth than that by the albumen route. In the NAI assay, the half maximal inhibitory concentration (IC50) values of the H9N2 viruses were within the standard range for known susceptible reference virus. In conclusion, the H9N2 viruses used in the study were susceptible to OC. Embryonated chicken egg could be used as a model to study susceptibility of AI viruses to antiviral drugs.

Immunogenicity and Protective Effect of Live Cold-Adapted Vaccines against Influenza B after Intranasal Immunization of Mice

Live attenuated («att») vaccines based on cold-adapted («ca») strains are a promising approach of influenza prophylaxis enhancement, however, effectiveness evaluation as well as interrelation with immunogenicity should be elucidated, especially for vaccines against type B influenza.Sterile, pure and concentrated viruses were prepared using a parent wild-type influenza type B and a live «ca» strain derived from the wild-type strain, and their biological activity and phenotype were fully characterized. Mice intranasally immunized twice with the live «ca» vaccines developed sterile immunity (wild-type virus was not isolated in chicken embryos (below limit of detection) from lungs of immunized and subsequently infected mice), however, sera antibodies in hemagglutination inhibition test (HAI) were also not detected (below limit of detection).Live «ca» vaccines against influenza type B viruses are effective, however, protection from infection was not determined by HAI antibodies. Further studies using various methods of immunogenicity evaluation and characterization of mechanisms of protection for influenza vaccines, first of all «att», are needed.

Investigating clinically adequate concentrations of oseltamivir carboxylate in end-stage renal disease patients undergoing hemodialysis using a population pharmacokinetic approach.

End-stage renal disease (ESRD) patients receiving hemodialysis (HD) are at heightened risk for influenza, but the optimal oseltamivir dosage regimen for treating or preventing influenza in this high-risk population is still uncertain. Pharmacokinetic data for 24 adults with ESRD were pooled from a single-dose and a multiple-dose study to develop a population pharmacokinetic model using nonlinear mixed-effects modeling. The final model comprised five compartments, two each to describe the systemic pharmacokinetics of oseltamivir phosphate and its metabolite, oseltamivir carboxylate (OC), and a delay compartment to describe oseltamivir metabolism. Estimated OC clearance in the model was markedly faster during HD sessions (7.43 liters/min) than at other times (0.19 liter/min). Model simulations showed that 30 mg oseltamivir given after every HD session is the most suitable regimen for influenza treatment, producing trough OC concentrations above the median value achieved with the 75-mg twice-daily regimen in patients with normal renal function and peak concentrations below the highest oseltamivir exposures known to be well tolerated (median exposures after twice-daily dosing of 450 mg). Administration of the first dose following diagnosis of influenza need not wait until after the next HD session: addition of a single 30-mg dose during the 12 h before the next HD session raises OC exposures quickly without posing any safety risk. Further simulation showed that 30 mg oseltamivir given after every other HD session is the most suitable regimen for influenza prophylaxis.

Oseltamivir for the treatment of H1N1 influenza during pregnancy.

Pregnancy heightens the risk of adverse outcomes from influenza infections. This is true for both seasonal epidemics as well as occasional pandemics. Seasonal influenza vaccines are the focus of disease prevention and are recommended for all pregnant women in any trimester of pregnancy and postpartum. Oseltamivir (Tamiflu) is currently the recommended and most commonly used pharmaceutical agent for influenza prophylaxis and treatment. Oseltamivir has been demonstrated to prevent disease after exposure, treat infected individuals, as well as lessen the likelihood of complications. The physiologic adaptations of pregnancy alter the pharmacokinetics of this important drug. Evidence of these alterations, knowledge gaps, and future investigative directions to fill these knowledge gaps are highlighted.

Identification of new oral dosing regimens for the neuraminidase inhibitor oseltamivir in patients with moderate and severe renal impairment.

Availability of lower-dose oseltamivir capsules, an increased pharmacokinetic database, and a desire to align drug exposure across the spectrum of renal function prompted reassessment of oral dosing in patients with renal impairment. The data set comprised 128 subjects (71 with varying degrees of renal impairment) from 8 studies, which included single and multiple doses of 20-1000 mg. Pharmacokinetic profiles of oseltamivir phosphate (OP) and oseltamivir carboxylate (OC) were modeled simultaneously in NONMEM. Exposure metrics of OP and OC (AUC48 h , Cmax , Cmin ) after administration of various dosing regimens were simulated for renal impairment subgroups and compared with exposures in patients with normal renal function receiving approved regimens. For influenza treatment, 30 mg once-daily and twice-daily regimens were selected for severe and moderate impairment, respectively. These regimens provided OC exposures similar or above those of the approved 75-mg twice-daily treatment regimen in subjects with normal renal function. For influenza prophylaxis, 30 mg once every other day and once-daily regimens were selected for severe and moderate impairment, respectively. No dosing adjustments were required for mild impairment. This analysis supported revised labeling in the United States and Europe for oral oseltamivir dosing in patients with moderate and severe renal impairment.

Acute exacerbation of psychiatric symptoms during influenza treatment with oseltamivir in chronic schizophrenia

Influenza treatment and prophylaxis with oseltamivir are critically important in reducing the morbidity and mortality of patients in chronic psychiatric facilities. Abnormal behavior, delusions, perceptual disturbances, mania, and depression have all been reported as oseltamivir-related psychiatric side effects. We hereby report two chronic schizophrenia patients in Taiwan manifesting psychiatric instability who were being treated with oseltamivir for suspected influenza infection, and further discuss other potential contributing factors. The possibility that oseltamivir can cause psychotic or affective symptoms suggests that additional caution is necessary for its use in patients with an established psychiatric diagnosis.

The Mechanisms of Adverse Reactions to Oseltamivir: Part II. Delayed Type Reactions

Oseltamivir is recommended for treatment and prophylaxis of Influenza in persons at higher risk for Influenza complications such as individuals with diabetes, neuropsychiatric illnesses, and respiratory, cardiac, renal, hepatic or hematological diseases. However, a recent systematic review reported that reduction of antibody production, renal disorders, hyperglycemia, psychiatric disorders, and QT prolongation may be related to Oseltamivir use. The underlying mechanisms of these effects are reviewed. There is decisive evidence that administration of a clinically compatible dose of Oseltamivir in mice challenged by a respiratory syncytial virus (RSV) that lacks a neuraminidase gene showed symptom-relieving effects and inhibition of viral clearance. These effects were accompanied by decreased level of T cell surface sialoglycosphingolipid (ganglioside) GM1 that is regulated by the endogenous neuraminidase in response to viral challenge. Clinical and non-clinical evidence supports the view that the usual dose of Oseltamivir suppresses pro-inflammatory cytokines such as interferon-gamma, interleukin-6, and tumor necrosis factor-alpha almost completely in experimentally infected Influenza viruses in humans with partial suppression of viral shedding. Animal toxicity tests support the clinical evidence with regard to renal and cardiac disorders (bradycardia and QT prolongation) and do not disprove the metabolic effect. Reduction of antibody production and cytokine induction and renal, metabolic, cardiac, and prolonged psychiatric disorders after Oseltamivir use may be related to inhibition of the host’s endogenous neuraminidase. While the usual clinical dose of Zanamivir may not have this effect, a higher dose or prolonged administration of Zanamivir and other neuraminidase inhibitors may induce similar delayed reactions, including reduction of antibody and/or cytokine production.

The Tamiflu fiasco and lessons learnt.

Oseltamivir (Tamiflu), a neuraminidase inhibitor, was approved for seasonal flu by US Food and Drug Administration in 1999. A number of randomized controlled trials, systematic reviews, and meta-analysis emphasized a favorable efficacy and safety profile. Majority of them were funded by Roche, which also first marketed and promoted this drug. In 2005 and 2009, the looming fear of pandemic flu led to recommendation by prominent regulatory bodies such as World Health Organization (WHO), Centers for Disease Control and Prevention, European Medicines Agency and others for its use in treatment and prophylaxis of influenza, and it's stockpiling as a measure to tide over the crisis. Serious Adverse Events, especially neuropsychiatric events associated with Tamiflu started getting reported leading to a cascade of questions on clinical utility of this drug. A recent Cochrane review and related articles have questioned the risk-benefit ratio of the drug, besides raising doubts about the regulatory decision of approving it. The recommendations for stockpiling the said drug as given by various international organizations viz WHO have also been put to scrutiny. Although many reviewers have labeled the Tamiflu saga as a “costly mistake,” the episode leaves us with some important lessons. This article takes a comprehensive relook on the subject, and we proceed to suggest some ways and means to avoid a similar situation in the future.

Preclinical activity of VX-787, a first-in-class, orally bioavailable inhibitor of the influenza virus polymerase PB2 subunit.

VX-787 is a novel inhibitor of influenza virus replication that blocks the PB2 cap-snatching activity of the influenza viral polymerase complex. Viral genetics and X-ray crystallography studies provide support for the idea that VX-787 occupies the 7-methyl GTP (m(7)GTP) cap-binding site of PB2. VX-787 binds the cap-binding domain of the PB2 subunit with a KD (dissociation constant) of 24 nM as determined by isothermal titration calorimetry (ITC). The cell-based EC50 (the concentration of compound that ensures 50% cell viability of an uninfected control) for VX-787 is 1.6 nM in a cytopathic effect (CPE) assay, with a similar EC50 in a viral RNA replication assay. VX-787 is active against a diverse panel of influenza A virus strains, including H1N1pdm09 and H5N1 strains, as well as strains with reduced susceptibility to neuraminidase inhibitors (NAIs). VX-787 was highly efficacious in both prophylaxis and treatment models of mouse influenza and was superior to the neuraminidase inhibitor, oseltamivir, including in delayed-start-to-treat experiments, with 100% survival at up to 96 h postinfection and partial survival in groups where the initiation of therapy was delayed up to 120 h postinfection. At different doses, VX-787 showed a 1-log to >5-log reduction in viral load (relative to vehicle controls) in mouse lungs. Overall, these favorable findings validate the PB2 subunit of the viral polymerase as a drug target for influenza therapy and support the continued development of VX-787 as a novel antiviral agent for the treatment of influenza infection.

Should we recommend neuroaminidase inhibitors for influenza?

A recent Cochrane systematic review challenged the evidence base for neuraminidase inhibitors (NIs) by claiming that NIs have negligible efficacy in the treatment of influenza [1]. An individual patient data meta-analysis seemingly contradicts these findings [2]. The public, physicians, policy-makers and governments are now struggling to understand how to translate these findings to clinical practice. Jefferson et al. [1] updated their Cochrane review of randomized controlled trials (RCTs) that compared NIs with placebo as treatment or prophylaxis for influenza, basing it on study reports sent to regulators in an attempt to include full data from all RCTs performed (60% of the data from RCTs on oseltamivir have not been published). The review included healthy children and adults of all ages, including people with chronic diseases that do not affect the immune system profoundly. Among adults (eight trials, 3954 participants), oseltamivir reduced the duration of symptoms by 16.8 h (95% CI 8.4– 25.1, no heterogeneity). Hospital admissions were identical in the placebo and NI treatment arms. Pneumonia rates were reported less frequently with treatment (numbers needed to treat (NNT) = 100), but the reduction was mainly observed in studies that did not collect this information systematically. Sinusitis and otitis media had the same rates. Nausea and vomiting were the most common adverse effects of the drug, but the rate of withdrawal because of adverse events was similar to that with placebo. The reduction in duration of symptoms for adults given zanamivir as inhalation or as nasal spray (13 studies, 5411 participants) was 14 h (95% CI 9– 28 h, low heterogeneity). A significant reduction was observed in bronchitis rates, but not in pneumonia rates. Serious adverse events and adverse events that led to withdrawal from the study were not more common in the active arm than in the placebo arm. When given for prophylaxis among adults and children, oseltamivir reduced the rate of symptomatic laboratory-confirmed influenza (relative risk (RR) 0.45 (95% CI 0.30–0.67, NNT c. 50), but not the rates of influenza-like illnesses, hospital admissions, or any other severe complication. Zanamivir reduced the rates of symptomatic influenza (RR 0.39, 95% CI 0.22–0.70, NNT c. 50) and pneumonia (RR 0.30, 95% CI 0.11–0.80, NNT 311). The rates of influenza-like illnesses were not available. Elderly participants were separately investigated in only four prophylaxis trials. Few elderly patients were included in the treatment trials, and the Cochrane review did not assess this subgroup. The original studies did not include persons with severe underlying disorders or patients with a severe presentation of influenza, e.g. those requiring hospital admission. Muthuri et al. [2]. conducted an individual patient-data meta-analysis of observational studies, including 29 234 people from 78 centres (including our dataset [3]) hospitalized because of influenza A H1N1 (81.5% laboratory-confirmed). Patients given NIs had a lower fatality rate than patients not treated with NIs (adjusted OR 0.81, 95% CI 0.70–0.93). Patients given treatment within 2 days of symptom onset had a lower fatality rate than those given later treatment (adjusted OR 0.48, 95% CI 0.41–0.56). The meta-analysis shares two weaknesses with the observational studies published on this issue. Patients were not randomized to treatment vs. no treatment or to early vs. late treatment. Physicians had reasons for prescribing NIs in certain patients and for not prescribing them in others. We cannot be sure that the techniques used (adjusting for the propensity for treatment and risk factors for mortality) can compensate in full for this bias. Another potential source of bias is the immortal time bias: patients given treatment and late treatment survived at least to the day on which the treatment was prescribed. Researchers might have published positive results but not negative ones, and researchers showing positive results might have been more inclined to share their data and include them in the meta-analysis (publication bias). We also do not know whether the results obtained during the H1N1 pandemic can be generalized to all influenza epidemics or pandemics. How should these data direct practice? For healthy people in the community, the modest reduction in symptom duration (out of the 7-day illness duration without treatment) with no other proven positive outcomes does not, in our opinion, justify treatment with NIs. In people admitted to hospital with severe influenza complications or severe