BACKGROUND:Neuraminidase inhibitors (NIs) are stockpiled and recommended by public health agencies for treating and preventing seasonal and pandemic influenza. They are used clinically worldwide.OBJECTIVE:To describe the potential benefits and harms of NIs for influenza in all age groups by reviewing all clinical study reports of published and unpublished randomised, placebo-controlled trials and regulatory comments.METHODSSearch methods: We searched trial registries, electronic databases (to 22 July 2013) and regulatory archives, and corresponded with manufacturers to identify all trials. We also requested clinical study reports. We focused on the primary data sources of manufacturers but we checked that there were no published randomised controlled trials (RCTs) from non-manufacturer sources by running electronic searches in the following databases: the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, MEDLINE (Ovid), EMBASE, Embase.com, PubMed (not MEDLINE), the Database of Reviews of Effects, the NHS Economic Evaluation Database and the Health Economic Evaluations Database.Selection criteria: Randomised, placebo-controlled trials on adults and children with confirmed or suspected exposure to naturally occurring influenza.Data collection and analysis: We extracted clinical study reports and assessed risk of bias using purpose-built instruments. We analysed the effects of zanamivir and oseltamivir on time to first alleviation of symptoms, influenza outcomes, complications, hospitalisations and adverse events in the intention-to-treat (ITT) population. All trials were sponsored by the manufacturers.MAIN RESULTS: We obtained 107 clinical study reports from the European Medicines Agency (EMA), GlaxoSmithKline and Roche. We accessed comments by the US Food and Drug Administration (FDA), EMA and Japanese regulator. We included 53 trials in Stage 1 (a judgement of appropriate study design) and 46 in Stage 2 (formal analysis), including 20 oseltamivir (9623 participants) and 26 zanamivir trials (14,628 participants). Inadequate reporting put most of the zanamivir studies and half of the oseltamivir studies at a high risk of selection bias. There were inadequate measures in place to protect 11 studies of oseltamivir from performance bias due to non-identical presentation of placebo. Attrition bias was high across the oseltamivir studies and there was also evidence of selective reporting for both the zanamivir and oseltamivir studies. The placebo interventions in both sets of trials may have contained active substances.Time to first symptom alleviation. For the treatment of adults, oseltamivir reduced the time to first alleviation of symptoms by 16.8 hours (95% confidence interval (CI) 8.4 to 25.1 hours, P < 0.0001). This represents a reduction in the time to first alleviation of symptoms from 7 to 6.3 days. There was no effect in asthmatic children, but in otherwise healthy children there was (reduction by a mean difference of 29 hours, 95% CI 12 to 47 hours, P = 0.001). Zanamivir reduced the time to first alleviation of symptoms in adults by 0.60 days (95% CI 0.39 to 0.81 days, P < 0.00001), equating to a reduction in the mean duration of symptoms from 6.6 to 6.0 days. The effect in children was not significant. In subgroup analysis we found no evidence of a difference in treatment effect for zanamivir on time to first alleviation of symptoms in adults in the influenza-infected and non-influenza-infected subgroups (P = 0.53).Hospitalisations. Treatment of adults with oseltamivir had no significant effect on hospitalisations: risk difference (RD) 0.15% (95% CI -0.78 to 0.91). There was also no significant effect in children or in prophylaxis. Zanamivir hospitalisation data were unreported.Serious influenza complications or those leading to study withdrawal.In adult treatment trials, oseltamivir did not significantly reduce those complications classified as serious or those which led to study withdrawal (RD 0.07%, 95% CI -0.78 to 0.44), nor in child treatment trials; neither did zanamivir in the treatment of adults or in prophylaxis. There were insufficient events to compare this outcome for oseltamivir in prophylaxis or zanamivir in the treatment of children.Pneumonia.Oseltamivir significantly reduced self reported, investigator-mediated, unverified pneumonia (RD 1.00%, 95% CI 0.22 to 1.49); number needed to treat to benefit (NNTB) = 100 (95% CI 67 to 451) in the treated population. The effect was not significant in the five trials that used a more detailed diagnostic form for pneumonia. There were no definitions of pneumonia (or other complications) in any trial. No oseltamivir treatment studies reported effects on radiologically confirmed pneumonia. There was no significant effect on unverified pneumonia in children. There was no significant effect of zanamivir on either self reported or radiologically confirmed pneumonia. In prophylaxis, zanamivir significantly reduced the risk of self reported, investigator-mediated, unverified pneumonia in adults (RD 0.32%, 95% CI 0.09 to 0.41); NNTB = 311 (95% CI 244 to 1086), but not oseltamivir.Bronchitis, sinusitis and otitis media.Zanamivir significantly reduced the risk of bronchitis in adult treatment trials (RD 1.80%, 95% CI 0.65 to 2.80); NNTB = 56 (36 to 155), but not oseltamivir. Neither NI significantly reduced the risk of otitis media and sinusitis in both adults and children.Harms of treatment.Oseltamivir in the treatment of adults increased the risk of nausea (RD 3.66%, 95% CI 0.90 to 7.39); number needed to treat to harm (NNTH) = 28 (95% CI 14 to 112) and vomiting (RD 4.56%, 95% CI 2.39 to 7.58); NNTH = 22 (14 to 42). The proportion of participants with four-fold increases in antibody titre was significantly lower in the treated group compared to the control group (RR 0.92, 95% CI 0.86 to 0.97, I2 statistic = 0%) (5% absolute difference between arms). Oseltamivir significantly decreased the risk of diarrhoea (RD 2.33%, 95% CI 0.14 to 3.81); NNTB = 43 (95% CI 27 to 709) and cardiac events (RD 0.68%, 95% CI 0.04 to 1.0); NNTB = 148 (101 to 2509) compared to placebo during the on-treatment period. There was a dose-response effect on psychiatric events in the two oseltamivir "pivotal" treatment trials, WV15670 and WV15671, at 150 mg (standard dose) and 300 mg daily (high dose) (P = 0.038). In the treatment of children, oseltamivir induced vomiting (RD 5.34%, 95% CI 1.75 to 10.29); NNTH = 19 (95% CI 10 to 57). There was a significantly lower proportion of children on oseltamivir with a four-fold increase in antibodies (RR 0.90, 95% CI 0.80 to 1.00, I2 = 0%).Prophylaxis.In prophylaxis trials, oseltamivir and zanamivir reduced the risk of symptomatic influenza in individuals (oseltamivir: RD 3.05% (95% CI 1.83 to 3.88); NNTB = 33 (26 to 55); zanamivir: RD 1.98% (95% CI 0.98 to 2.54); NNTB = 51 (40 to 103)) and in households (oseltamivir: RD 13.6% (95% CI 9.52 to 15.47); NNTB = 7 (6 to 11); zanamivir: RD 14.84% (95% CI 12.18 to 16.55); NNTB = 7 (7 to 9)). There was no significant effect on asymptomatic influenza (oseltamivir: RR 1.14 (95% CI 0.39 to 3.33); zanamivir: RR 0.97 (95% CI 0.76 to 1.24)). Non-influenza, influenza-like illness could not be assessed due to data not being fully reported. In oseltamivir prophylaxis studies, psychiatric adverse events were increased in the combined on- and off-treatment periods (RD 1.06%, 95% CI 0.07 to 2.76); NNTH = 94 (95% CI 36 to 1538) in the study treatment population. Oseltamivir increased the risk of headaches whilst on treatment (RD 3.15%, 95% CI 0.88 to 5.78); NNTH = 32 (95% CI 18 to 115), renal events whilst on treatment (RD 0.67%, 95% CI -2.93 to 0.01); NNTH = 150 (NNTH 35 to NNTB > 1000) and nausea whilst on treatment (RD 4.15%, 95% CI 0.86 to 9.51); NNTH = 25 (95% CI 11 to 116).AUTHORS' CONCLUSIONS: Oseltamivir and zanamivir have small, non-specific effects on reducing the time to alleviation of influenza symptoms in adults, but not in asthmatic children. Using either drug as prophylaxis reduces the risk of developing symptomatic influenza. Treatment trials with oseltamivir or zanamivir do not settle the question of whether the complications of influenza (such as pneumonia) are reduced, because of a lack of diagnostic definitions. The use of oseltamivir increases the risk of adverse effects, such as nausea, vomiting, psychiatric effects and renal events in adults and vomiting in children. The lower bioavailability may explain the lower toxicity of zanamivir compared to oseltamivir. The balance between benefits and harms should be considered when making decisions about use of both NIs for either the prophylaxis or treatment of influenza. The influenza virus-specific mechanism of action proposed by the producers does not fit the clinical evidence.

There has been considerable controversy over the past year, particularly in Europe, over whether the World Health Organization (WHO) changed its definition of pandemic influenza in 2009, after novel H1N1 influenza was identified. Some have argued that not only was the definition changed, but that it was done to pave the way for declaring a pandemic. Others claim that the definition was never changed and that this allegation is completely unfounded. Such polarized views have hampered our ability to draw important conclusions. This impasse, combined with concerns over potential conflicts of interest and doubts about the proportionality of the response to the H1N1 influenza outbreak, has undermined the public trust in health officials and our collective capacity to effectively respond to future disease threats. WHO did not change its definition of pandemic influenza for the simple reason that it has never formally defined pandemic influenza. While WHO has put forth many descriptions of pandemic influenza, it has never established a formal definition and the criteria for declaring a pandemic caused by the H1N1 virus derived from "pandemic phase" definitions, not from a definition of "pandemic influenza". The fact that despite ten years of pandemic preparedness activities no formal definition of pandemic influenza has been formulated reveals important underlying assumptions about the nature of this infectious disease. In particular, the limitations of "virus-centric" approaches merit further attention and should inform ongoing efforts to "learn lessons" that will guide the response to future outbreaks of novel infectious diseases.

Durante el pasado año, fundamentalmente en Europa, se generó una considerable polémica sobre si la Organización Mundial de la Salud (OMS) habría cambiado su definición de gripe pandémica en el año 2009, tras la identificación de la nueva gripe H1N1. Algunos argumentan que no solo se cambió la definición, sino que se hizo para despejar el camino hacia la declaración de una pandemia. Otros aseguran que la definición nunca se cambió y que esta alegación está completamente infundada. Estos puntos de vista tan opuestos han dificultado nuestra capacidad para extraer conclusiones relevantes. Este callejón sin salida, unido a las preocupaciones sobre los posibles conflictos de intereses y las dudas sobre la proporcionalidad de la respuesta al brote de la gripe H1N1, ha menoscabado la confianza de la población en los responsables de la salud y en nuestra capacidad colectiva para responder con eficacia a futuras amenazas de este tipo. La OMS no cambió su definición de gripe pandémica por el simple motivo de que nunca antes había definido formalmente el concepto de gripe pandémica. Si bien la OMS ha propuesto numerosas descripciones de gripe pandémica, nunca estableció una definición formal y los criterios para la declaración de una pandemia provocada por el virus H1N1 procedían de las definiciones de «fase de alerta pandémica», no de una definición de «gripe pandémica». El hecho de no contar con una definición formal de gripe pandémica, a pesar del bagaje de los diez años de actividades de preparación contra las pandemias, revela importantes suposiciones subyacentes sobre la naturaleza de esta enfermedad infecciosa. En particular, las limitaciones de los enfoques «centrados en el virus» reclaman una mayor atención y se debe informar sobre los esfuerzos que se realicen para «aprender las lecciones» que dirijan nuestra respuesta ante los futuros brotes de nuevas enfermedades infecciosas.

Depuis l'an dernier, il existe une importante controverse, en particulier en Europe: l'Organisation mondiale de la Santé (OMS) a-t-elle changé ou non sa définition de la grippe pandémique en 2009, après l'identification de la grippe H1N1 originale? Certains ont soutenu que non seulement cette définition a été modifiée, mais qu'elle l'a été dans le but de préparer la déclaration d'une pandémie. D'autres ont expliqué que la définition n'a jamais été changée et que cette allégation est dénuée de tout fondement. Ces vues polarisées ont gêné notre capacité à tirer des conclusions importantes. Cette impasse, associée aux préoccupations sur les conflits d'intérêts potentiels et aux doutes sur la proportionnalité de la réponse à l'apparition de la grippe H1N1, a sapé la confiance publique envers les autorités sanitaires et envers notre capacité collective à répondre de manière efficace aux menaces des maladies futures. L'OMS n'a pas modifié sa définition de la grippe pandémique pour la simple raison qu'elle ne l'a jamais définie de manière officielle. Alors que l'OMS a proposé de nombreuses descriptions de la grippe pandémique, elle n'a jamais élaboré une définition formelle. De plus, les critères de déclaration d'une pandémie causée par le virus H1N1 ont leur origine dans les définitions de la «phase pandémique», et non dans une définition de la «grippe pandémique». Le fait que, malgré dix années d'activités de préparation à une pandémie, aucune définition officielle de la grippe pandémique n'ait été formulée révèle des hypothèses sous-jacentes importantes sur la nature de cette maladie infectieuse. Les limitations des approches «axées sur les virus» méritent en particulier une plus grande attention et doivent contribuer aux efforts incessants pour «tirer des leçons» qui guideront la réponse aux apparitions futures de nouvelles maladies infectieuses.