Diffusion of a Pandemic Through a Global Transportation Network

The above map provides a synthetic representation about how an (influenza) pandemic could spread through a global transportation network. The assumption in this scenario is a virulent strain of influenza in the line of the Spanish Flu (H1N1) with an incubation phase of about 3 to 4 days and that can easily been transmitted from human to human. The pandemic is divided into four succinct phases:

• Emergence. There are several ecological regions where new strains of influenza can emerge, particularly in Southeast Asia and Southern China. In the current transportation and economic context southern China is prone to risks. It has become one of the largest manufacturing cluster in the world, notably in the Pearl River Delta. This implies intense trade and business transactions and significant migrations of people from different regions of China as well as networks of people living in different countries that have kept roots (relatives) in the countryside. Additionally, large international transport terminals, including one of the largest airport in the world (Hong Kong), are in proximity. If the infection jumps right away at a gateway, then the diffusion could be rapid and extensive before being acknowledged as a significant health threat.
• Translocation. This phase involves a group of infected individuals, many still in the incubation phase without showing symptoms, entering the global air transport system over a period of a few days. The virus will be transmitted to several other individuals while in transit (in planes and at intermediary terminals) and at the destinations. The pandemic is translocated not necessarily by geographical proximity, but according to the structure of the international air transport network. It becomes a matter of flight scheduling and the destination served from the gateway the pandemic is translocated from. The pattern of this translocation will initially be shaped by social and commercial interactions, implying that depending on where the virus has emergence the translocation will be different. Several health authorities begin to issue warnings and try to assess the scale and scope of the infection. It is likely at this point that several segments of the air transport system would be voluntarily shut down or seriously curtailed by flight cancellations and the unwillingness to travel to high risk areas. If identified early and not affecting too many individuals, it is possible to stop the diffusion of the pandemic or seriously curtain its advance.
• Diffusion. At this point translocation has brought the influenza infection in almost every major transport hub of the world. From multiple hubs, the pandemic diffuse in a more standard fashion linked through proximity and slower land transport systems (rail, road, public transit). From a pandemic control standpoint, it is essentially too late to do anything since its extent is now global and a large mass of individuals have already been infected. The pandemic becomes apparent to the general public, emergency measures are put into action and most transport (from airlines to public transit) and economic systems (beginning with non-essential services such a leisure) are starting to shut down, either through decree or voluntarily (more likely).
• Pandemic. It this point a pandemic is a reality with few locations unaffected, either by chance, quarantine, isolation or containment. The matter is no longer mitigating the pandemic, but providing medical relief as well as maintaining essential supply chains, namely food, energy and medical supplies. Passenger transportation slows down to a trickle and essential freight distribution function more or less successfully depending on the level of preparedness and the resilience of contingency plans of specific countries. It is very difficult to assess what the world would look like at such a stage as it would obviously depend on the virulence and lethality of the pandemic and how the public and private sectors have responded. The outcome could range from the benign to the serious; from a slowdown followed by a rather quick recovery to a social collapse in large areas caused by shortages of food, energy and medical supplies. Since it has been close to 90 years since the last serious pandemic (1918-1920) and that the world was then a very different place with much lower independencies, there is limited ground to extrapolate the consequences of such a pandemic in a globalized economy.