John Libbey Eurotext

Environnement, Risques & Santé

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Mathematical modelling of the spatio‐temporal spread of smallpox epidemics Volume 2, issue 4, Juillet 2003

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Épidémiologie et sciences de l‘information, INSERM U444, CHU Saint‐Antoine, Université Pierre et Marie Curie, 27, rue Chaligny, 75012 Paris, France Centre collaborateur OMS pour la surveillance électronique des maladies <legrandu444.jussieu.fr>
  • Key words: smallpox; variola virus; bioterrorism; biological warfare; mathematical model; disease outbreaks.
  • Page(s) : 211-20
  • Published in: 2003

Smallpox, which was eradicated in 1979, is a communicable disease that could be used as a biological weapon. Several recent models of smallpox epidemics have attempted to evaluate the efficacy of various possible interventions to control it, but they do not take the spatial component of the epidemic‘s dynamics into account. Individual mobility has increased since smallpox eradication and may promote the extension of the epidemic over large areas. If smallpox reappeared in France, the issue of limiting travel might arise. To evaluate this type of intervention, we developed a deterministic spatio‐temporal SEIR model (susceptible, exposed, infectious, removed) that can simulate ring vaccination and isolation of cases. We applied this model to the 21 French administrative regions (excluding Corsica) to forecast the impact of a bioterrorist attack in the Paris metropolitan area. After a sensitivity analysis of various model parameters (number of index cases, R 0, intervention efficacy), we concluded that restricting travel would not effectively limit the size of the epidemic. The reference model assumed that 100 persons were initially contaminated in the Paris area, with R 0 equal to 3, 80% of contacts vaccinated and 60% of those infectious isolated at 25 days after the initial attack. In this case, 730 cases of smallpox would occur (395 cases in the Paris region), 5,500 doses of vaccine would be used and 550 persons isolated. Reducing the movements of contacts by 90% (25 days after the attack) would not substantially decrease the epidemic size.