Published 8 September 2009, doi:10.1136/bmj.b3620
Cite this as: BMJ 2009;339:b3620

Letters

A/H1N1 flu pandemic

Antiviral drugs: distinguish treatment from prophylaxis

Shun-Shin and colleagues provide a timely review of the effectiveness of neuraminidase inhibitors for treatment and chemoprophylaxis of flu virus infections.¹ As the pandemic A/H1N1 flu virus seems to have remained susceptible in vitro to neuraminidase inhibitors we expect that effectiveness against the pandemic virus would be similar to that against seasonal influenza A strains. There should by now be sufficient observational data to demonstrate this. Further trials to detect differences in effectiveness between pandemic and seasonal strains would need to be very large.

Distinguishing the use of antiviral drugs for treatment from their use as chemoprophylaxis against infection or illness is important. In the current pandemic oseltamivir treatment has been widely used in many countries as part of "mitigation phase" protocols whereas chemoprophylaxis has rarely been used since the initial "containment phase." Shun-Shin and colleagues’ conclusion that neuraminidase inhibitors shorten the duration of illness and reduce household transmission does not clarify that transmission refers to chemoprophylaxis whereas duration refers to treatment, as the review did not cover indirect benefits of treatment.¹ Oseltamivir treatment alone may lead to moderate reductions in transmission to household contacts.²

The 8% reduction in household transmission associated with chemoprophylaxis is an estimate of the absolute risk reduction, from around 12% in the placebo arm to around 4% in the antiviral arm,¹ corresponding to a relative risk reduction of almost 70%. However, in pandemics, secondary attack rates are typically higher because of the lack of population immunity,³ and absolute risk reductions associated with chemoprophylaxis may be greater.

Cite this as: BMJ 2009;339:b3620

¹ School of Public Health, University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China, ² Vaccine and Infectious Disease Institute, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA

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Competing interests: None declared.

References

1. Shun-Shin M, Thompson M, Heneghan C, Perera R, Harnden A, Mant D. Neuraminidase inhibitors for treatment and prophylaxis of influenza in children: systematic review and meta-analysis of randomised controlled trials. BMJ 2009;339:b3172. (11 August.)[Abstract/Free Full Text]
2. Halloran ME, Hayden FG, Yang Y, Longini IM Jr, Monto AS. Antiviral effects on influenza viral transmission and pathogenicity: observations from household-based trials. Am J Epidemiol 2007;165:212-21.[Abstract/Free Full Text]
3. World Health Organization. Assessing the severity of an influenza pandemic. 2009. Available from: www.who.int/csr/disease/swineflu/assess/disease_swineflu_assess_20090511/en/index.html

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Relevant Article

Neuraminidase inhibitors for treatment and prophylaxis of influenza in children: systematic review and meta-analysis of randomised controlled trials

Matthew Shun-Shin, Matthew Thompson, Carl Heneghan, Rafael Perera, Anthony Harnden, and David Mant
BMJ 2009 339: b3172. [Abstract] [Full Text] [PDF]

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