Prevention and early treatment of influenza in healthy adults

Introduction: We present three systematic reviews carried out within the Co chrane Collaboration, focusing on a different influenza intervention in hea lthy adults: Vaccines; Ion Channel Inhibitor antivirals and Neuraminidase I nhibitor (NIs) antivirals. The objectives were to identify, retrieve and as sess all studies evaluating the effects of these interventions in prophylax is and early treatments of influenza and the frequency of adverse events. A dditionally we present the results of the economic evaluation of effective alternatives in order to define the most cost-effective intervention. The e conomic evaluation is set in the context of the British Army. Methods: Studies were identified using a standard Cochrane search strategy. Any randomised or quasi-randomised studies in healthy individuals aged 14- 60 years were considered for inclusion in the systematic review. Those whic h met inclusion criteria were assessed for quality and their data meta-anal ysed. The economic model was constructed using Cost-effectiveness and Cost- utility study designs, Results: Live aerosol vaccines reduced cases of clinical influenza A with v irological confirmation (by serology and/or viral isolation) by 48% (95%CI, 24-64%), whilst recommended inactivated parenteral vaccines have an effica cy of 68% (95%CI, 49-79%). Vaccine effectiveness in reducing clinical influ enza cases (i.e. without virological confirmation) was lower, with efficaci es of 13 and 24% respectively. Use of the vaccine significantly reduced tim e off work, but only by 0.4 days (95%CI, 0.1-0.8 days). Analysis of vaccine s matching the circulating strain gave higher estimates of efficacy, whilst inclusion of all other vaccines reduced the efficacy. When compared to pla cebo for the prevention of influenza, oral amantadine was 61% (95%CI: 51-69 %) efficacious (RR 0.39 - 95%CI: 0.31-0.49), and oral rimantadine was 64% ( 95%CI: 41-78%) efficacious (RR 0.36 - 95%CI: 0.22-0.59), When compared to p lacebo for the treatment of influenza, oral amantadine significantly shorte ned duration of fever (by 1.00 days - 95%CI: 0.73-1.29), and oral rimantadi ne significantly shortened duration of fever (by 1.27 days - 95%CI: 0.77-1. 77), When compared to placebo, NIs were 74% (95%CIs: 50-87%) effective in p reventing naturally occurring cases of clinically defined influenza. In a t reatment role, NIs shortened the duration of symptoms by one day (Weighted Mean Difference - 1.0; 95%CIs: -1.3 to - 0.6) when a clinical case definiti on is used. The economic results show that in healthy adults, inactivated v accines appear the best buy. Conclusions: If assessed from the point of view of effectiveness and effici ency, vaccines are undoubtedly the best preventive means for clinical influ enza in healthy adults. However, when safety and quality of life considerat ions are included, parenteral vaccines hate such low effectiveness and high incidence of trivial local adverse effects that the trade-off is unfavoura ble, This is so even when the incidence of influenza is high and adverse ef fect quality of life preferences are rated low. We reached similar conclusi ons for antivirals and NIs even at high influenza incidence levels. On curr ent evidence we conclude in healthy adults aged 14-60 the most cost-effecti ve option is not to take any action. (C) 2000 Elsevier Science Ltd. All rig hts reserved.