Accessibility statement

The evidence base for influenza intervention

Posted on 1 May 2009

A statement on the most up to date evidence on prevention and treatment.

The outbreaks of H1N1 swine influenza in Mexico and its spread to other countries have raised the World Health Organisation pandemic alert level to phase 5. A number of cases have now been confirmed across the UK.

In this statement, we collate the most up to date evidence on prevention and treatment from the internationally renowned CRD Databases. We focus on the effectiveness of two drugs used to prevent and treat influenza - oseltamivir (tamiflu) and zanamivir (relenza).


The most up to date record included in DARE on prevention is from a Health Technology Assessment report of the prophylactic use of antiviral drugs published in February 2009.1

The systematic review reported a 7% absolute reduction in the risk of contracting influenza with oseltamivir and zanamivir when compared to placebo, in people from mixed households that had been in contact with an influenza-like-illness, reducing the risk of contracting influenza from approximately 9% to 2%.1

Evidence was limited for the prevention of complications, hospital admissions and in minimizing length of illness and time to return to normal activities. There were no data relating to mortality.1


The most up to date assessment of treatment2 was commissioned to inform NICE guidance issued in February 2009.3 The systematic review is due to be published in August 2009.

The evidence from the systematic review of the use of antiviral drugs for the treatment of influenza found that when compared to placebo, on average zanamivir or oseltamivir reduced the time to alleviation of influenza symptoms by approximately half a day in otherwise healthy adults.2 For people considered ‘at risk’ of influenza-related complications, the time to alleviation of symptoms was reduced by up to one day.

There were insufficient data available from which to draw conclusions regarding the potential of either treatment to reduce the incidence of complications such as bronchitis or pneumonia.

There were no data relating to mortality.2

Neither the prevention or treatment systematic reviews, nor the clinical trials they considered, were in the context of an influenza pandemic (all the evidence relates to ‘normal’ seasonal outbreak of flu).

Professor Lesley Stewart said “Although the research evidence derives from a relatively small number of trials and participants, this evidence is still likely to be useful in informing current discussions.”

The CRD Databases contain other critically appraised systematic reviews and economic evaluations relevant to influenza. 

Notes to editors:

  1. Tappenden P, Jackson R, Cooper K, Rees A, Simpson E, Read R, et al. Amantadine, oseltamivir and zanamivir for the prophylaxis of influenza (including a review of existing guidance no. 67). Health Technology Assessment 2009; 13:1-312. Available at:
  2. Burch J, Paulden M, Conti S, Stock C, Corbett M, Welton NJ, et al. Antiviral drugs for the treatment of influenza: a systematic review and economic evaluation. Health Technology Assessment 2009;13(58). Available at:
  3. National Institute for Health and Clinical Excellence. NICE technology appraisal guidance 168. Amantadine, oseltamivir and zanamivir for the treatment of influenza (review of NICE technology appraisal guidance 58). February 2009 . Available at:
  4. The CRD Databases provide a single point of access to worldwide health research evidence, including critical abstracts of systematic reviews of effects and records of Cochrane reviews and protocols (DARE), critical abstracts of economic evaluations (NHS EED) and records of completed and ongoing health technology assessments (HTA database). For more information visit:
  5. The Centre for Reviews and Dissemination is part of the National Institute for Health Research (NIHR) and is a department of the University of York. The Centre aims to provide decision makers with research-based information about the effects of interventions used in health and social care. For more information visit:
  6. The views expressed in this statement are those of CRD and not necessarily those of the University of York, Department of Health or NIHR.
  7. Further information can be obtained from Alison Booth or Paul Wilson, Tel: 01904 321040; email: