Posted on 1 May 2009
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.