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Will travel restrictions control the international spread of pandemic influenza?

Nature Medicine volume 12, pages 497–499 (2006)Cite this article

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A key question in contingency planning for a possible influenza pandemic is the value of restricting international travel to and from affected countries or regions, or imposing entry or exit screening of passengers at airports1. The potential for infectious diseases to spread rapidly through an increasingly well-connected, steadily growing world population2,3,4,5 was brought into sharp focus during the 2003 epidemic of severe acute respiratory syndrome (SARS). By 12 March, 150 suspected cases had been reported in seven countries. By the end of the outbreak, 27 countries had reported 8,096 suspected cases6 and five incidents of transmission on commercial aircraft7. The World Health Organization (WHO) issued several travel advisories in an attempt to slow the international spread of the disease8. These were controversial because of their adverse economic impact and the uncertainty about their effectiveness. Here we analyze the impact of WHO travel advisories in 2003, and evaluate the likely effect of similar interventions in the case of an influenza pandemic.

Case isolation was highly effective in reducing onward transmission of SARS, and most imported cases were contained at their destination6 because infectiousness peaked well after the onset of clinical symptoms. In contrast, considerable infectiousness can be associated with presymptomatic or mildly symptomatic influenza infection5,9. Secondary influenza infections would be more likely to arise on international flights and from imported cases, accelerating international spread well beyond that seen for SARS. Conversely, the incubation period of influenza is short compared with SARS (∼1.5 d10,11 rather than 4 d12), which reduces the probability an asymptomatic person will travel. This effect, however, is more than offset by the much faster epidemic growth rate for pandemic influenza—potentially an average doubling time as short as 2.3 d (compared with 5.8 d for SARS; Fig. 1b and Supplementary Note online).

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Figure 1: International travel and epidemic spread.

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Acknowledgements

We gratefully acknowledge funding from the European Union (to T.D.H., N.M.F., R.M.A.), the Wellcome Trust (to T.D.H., R.M.A.) and the Medical Research Council (N.M.F.) We also thank the referees for their comments.

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  1. Department of Infectious Disease Epidemiology, Faculty of Medicine, St Mary's Campus, Imperial College, London, W2 1PG

    T Déirdre Hollingsworth, Neil M Ferguson & Roy M Anderson

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  1. T Déirdre Hollingsworth
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Hollingsworth, T., Ferguson, N. & Anderson, R. Will travel restrictions control the international spread of pandemic influenza?. Nat Med 12, 497–499 (2006). https://doi.org/10.1038/nm0506-497

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