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BMC Infectious Diseases

BioMed Central

Research article

Open Access

Small islands and pandemic influenza: Potential benefits and limitations of travel volume reduction as a border control measure Martin Eichner1, Markus Schwehm2, Nick Wilson*3 and Michael G Baker3

Address: 1Department of Medical Biometry, University of Tübingen, Germany, 2ExploSYS GmbH, Institute for Explorative Modeling, Leinfelden, Germany and 3Department of Public Health, University of Otago, Wellington, New Zealand

Email: Martin Eichner - martin.eichner@uni-tuebingen.de; Markus Schwehm - markus.schwehm@explosys.de; Nick Wilson* - nwilson@actrix.gen.nz; Michael G Baker - michael.baker@otago.ac.nz

  • *

    Corresponding author

Published: 29 September 2009 BMC Infectious Diseases 2009, 9:160

doi:10.1186/1471-2334-9-160

Received: 27 May 2009 Accepted: 29 September 2009

This article is available from: http://www.biomedcentral.com/1471-2334/9/160

© 2009 Eichner et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background: Some island nations have explicit components of their influenza pandemic plans for providing travel warnings and restricting incoming travellers. But the potential value of such restrictions has not been quantified.

Methods: We developed a probabilistic model and used parameters from a published model (i.e., InfluSim) and travel data from Pacific Island Countries and Territories (PICTs).

Results: The results indicate that of the 17 PICTs with travel data, only six would be likely to escape a major pandemic with a viral strain of relatively low contagiousness (i.e., for R0 = 1.5) even when imposing very tight travel volume reductions of 99% throughout the course of the pandemic. For a more contagious viral strain (R0 = 2.25) only five PICTs would have a probability of over 50% to escape. The total number of travellers during the pandemic must not exceed 115 (for R0 = 3.0) or 380 (for R0 = 1.5) if a PICT aims to keep the probability of pandemic arrival below 50%.

Conclusion: These results suggest that relatively few island nations could successfully rely on intensive travel volume restrictions alone to avoid the arrival of pandemic influenza (or subsequent waves). Therefore most island nations may need to plan for multiple additional interventions (e.g., screening and quarantine) to raise the probability of remaining pandemic free or achieving substantial delay in pandemic arrival.

Background There were large (voluntary) reductions of travel volumes associated with the global spread of severe acute respira- tory syndrome (SARS) [1]. There have also been media reports of reduced tourist flows associated with the swine- origin (H1N1) influenza pandemic during 2009 (particu- larly for Mexico). Such a phenomenon may reoccur with the emergence of more virulent waves of the current pan- demic or if new strains of pandemic influenza emerge.

In addition to voluntary changes in travel volumes, gov- ernments may also impose legal restrictions on travel and use exit and entry screening. Indeed, some island nations have explicit components of their influenza pandemic plans for providing travel warnings and restricting incom- ing travellers e.g., New Zealand [2] and all four Pacific Island Countries and Territories (PICTs) with published plans that were examined in a recent review [3]. Further- more, some modelling work suggests that international

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