Data on reducing the spread, infectiousness and pathogenicity of the virus could have important public health and pandemic preparedness implications -
New data published this week in the American Journal of Epidemiology has shown that antiviral drugs Tamiflu® (oseltamivir) and Relenza® (zanamivir) are highly effective at reducing the spread of influenza in households exposed to the influenza virus, an important aspect of intervention in pandemic influenza1. Analysing four household-based studies, the authors demonstrated that Tamiflu reduced the chance of an exposed person becoming ill with influenza by 81% compared with 75% for Relenza1. These data also show that antiviral drugs reduce the infectiousness (ability to transmit) and pathogenicity (ability to cause disease) of the influenza virus. Efficacy in reducing pathogenicity was 79% and 56% in the two Tamiflu studies; for Relenza, it was 52% and 56%1. Only Tamiflu significantly reduced the infectiousness of the virus, with an 80% reduction seen1. The effect was not significant with Relenza, demonstrating only a 19% reduction1.
Considering reasons for the greater impact of Tamiflu on infectiousness, the authors speculated that the oral formulation of Tamiflu could ensure it works successfully throughout the respiratory tract, versus the inhaled formulation of Relenza, which could make it less effective at targeting the influenza virus in the nose.1
Commenting on the results, John Melville, Roche UK General Manager said; “This study adds to the wealth of evidence that Tamiflu is extremely effective in the prevention of seasonal influenza. In addition, the data on reducing infectiousness and pathogenicity also has important public-health implications and highlights the important role Tamiflu will have in a future influenza pandemic, when controlling and limiting the spread of influenza will be paramount.”
Both the Department of Health, and the World Health Organization (WHO), recognise the important role of antiviral drugs in the management of pandemic influenza2, 3. The fulfilment of the first Department of Health Tamiflu stockpile order late last year, as part of the UK pandemic contingency plan, meant an important milestone in pandemic preparedness to protect the public was achieved, in line with WHO recommendations3.
According to recently published WHO guidelines on management of avian influenza, Tamiflu is recommended for the treatment of patients with confirmed or strongly suspected avian influenza A (H5N1); Relenza received a weak recommendation as an alternative due to a lower level of evidence for Relenza. Patients must also be able to use a disk haler to administer Relenza4. When given to prevent H5N1 influenza, Tamiflu was recommended for high- and moderate-risk exposure groups, including pregnant women, for seven to 10 days following exposure to the virus4.
Notes To Editors
The report evaluated data from four household-based, randomised, placebo-controlled clinical trials, conducted from 2000 to 2004, which were designed to estimate the effect of post-exposure antiviral treatment on preventing influenza within households. Two of the trials were conducted with zanamivir and two with oseltamivir, permitting comparisons to be made between the two. The trials covered a total of 1,475 households. The majority of index cases - first case in the household - (53% to 70%) had influenza A (H3N2 or H1N1).
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1. Halloran M et al. American Journal of Epidemiology. 2007 165(2):212-221
2. UK Health Department’s Influenza pandemic contingency plan. DH/ HPIH&SD / Immunisation Policy, Monitoring & Surveillance. 20 Oct 2005.
3. WHO global influenza preparedness plan. The role of WHO and recommendations for national measures before and during pandemics. http://www.who.int/csr/resources/publications/influenza/WHO_CDS_CSR_GIP_2005_5.pdf
4. Schunemann HJ et al. Lancet Infect Dis 2007;7:21-31