Human Mobility Networks, Travel Restrictions, and the Global Spread of 2009 H1N1 Pandemic

Paolo Bajardi1,2, Chiara Poletto1, José J. Ramasco3, Michele Tizzoni1,4, Vittoria Colizza5,6,7 and Alessandro Vespignani8,9,10
1Computational Epidemiology Laboratory, ISI Foundation, Turin, Italy
2Centre de Physique Théorique, Université d'Aix-Marseille, Marseille, France
3Instituto de Física Interdisciplinar y Sistemas Complejos IFISC (CSIC-UIB), Palma de Mallorca, Spain
4Scuola di Dottorato, Politecnico di Torin, Turin, Italy
5INSERM, U707, Paris, France
6UPMC Université Paris 06, Faculté, de Médecine Pierre et Marie Curie, UMR S 707, Paris, France
7Complex Systems Lagrange Laboratory, ISI Foundation, Turin, Italy
8Center for Complex Networks and Systems Research, School of Informatics and Computing, Indiana University, Bloomington IN, USA
9Pervasive Technology Institute, Indiana University, Bloomington IN, USA
10ISI Foundation, Turin, Italy

(February 2011)

After the emergence of the H1N1 influenza in 2009, some countries responded with travel-related controls during the early stage of the outbreak in an attempt to contain or slow down its international spread. These controls along with self- imposed travel limitations contributed to a decline of about 40% in international air traffic to/from Mexico following the international alert. However, no containment was achieved by such restrictions and the virus was able to reach pandemic proportions in a short time. When gauging the value and efficacy of mobility and travel restrictions it is crucial to rely on epidemic models that integrate the wide range of features characterizing human mobility and the many options available to public health organizations for responding to a pandemic. Here we present a comprehensive computational and theoretical study of the role of travel restrictions in halting and delaying pandemics by using a model that explicitly integrates air travel and short-range mobility data with high-resolution demographic data across the world and that is validated by the accumulation of data from the 2009 H1N1 pandemic. We explore alternative scenarios for the 2009 H1N1 pandemic by assessing the potential impact of mobility restrictions that vary with respect to their magnitude and their position in the pandemic timeline. We provide a quantitative discussion of the delay obtained by different mobility restrictions and the likelihood of containing outbreaks of infectious diseases at their source, confirming the limited value and feasibility of international travel restrictions. These results are rationalized in the theoretical framework characterizing the invasion dynamics of the epidemics at the metapopulation level.