New publication on human mobility restrictions measures against the global spreading of H1N1pdm influenza
Travel-related and mobility restriction policies are often considered to be the first line of defence against the spread of an emerging infectious disease. The wide range of implementation scenarios of such policies calls for models that are able to anticipate their actual effectiveness. The GLEaM team tackles this problem in the recent publication:
Human mobility networks, travel restrictions and the global spread of 2009 H1N1 pandemic
Paolo Bajardi, Chiara Poletto, Jose J Ramasco, Michele Tizzoni, Vittoria Colizza, Alessandro Vespignani
PLoS ONE 6(1): e16591 (2011).
During the early phase of the 2009 H1N1 pandemic outbreak, some countries implemented travel-related measures to prevent the infection from crossing the national borders. Many governments advised against non-essential travel to Mexico and activated airports entry screening to detect the potentially infected travelers. Even a few countries banned every flight connection to/from Mexico. All these measures, with the addition of self-imposed travel limitations due to the pandemic concerns following the international alert, contributed to an almost 40% reduction in the international passengers flying to and from Mexico. However, no containment was achieved by such restrictions and the virus was able to reach pandemic proportions in a short time.
GLEaM is suitable to simulate the spreading of an influenza-like illness and, in particular, it has been calibrated to simulate the 2009 H1N1 pandemic considering the etiology of the disease and the initial conditions. Taking advantage of the high detailed mobility data at the global level integrated in the model structure, Bajardi and coworkers assessed the impact of different travel reduction policies in the unfolding of the simulated pandemics. The work shows that feasible mobility limitations, highly disruptive in economic terms, generally are not effective: even with strong and lasting restrictions (a 90% reduction in the international air traffic to/from Mexico starting with the international alert and kept to the end of the epidemic was tested) the delay achieved is limited to two weeks .
In a pandemic scenario, this delay can be used to allocate resources and to enhance the surveillance systems, but it is definitely too short to develop a vaccine. Finally, the paper provides a quantitative discussion devoted to explain how the large heterogeneity of human mobility patterns is responsible for the ineffectiveness of travel restrictions. It is unlikely that, given the ever-increasing mobility of people around the world, travel restrictions could be used effectively in a future pandemic event.