The above map provides a synthetic representation of how an (influenza) pandemic could spread through a global transportation network. This scenario assumes a virulent strain of influenza in the line of the Spanish Flu (H1N1) with an incubation phase of about 3 to 4 days, which can easily be anthropogenically transmitted (R0 of 2 or above). The risk can be even higher if the incubation phase is longer and asymptomatic. A pandemic can be divided into four succinct phases:
- A. Emergence. Concerns the area where the contagion first emerged and the epidemiology involved before the virus is noticed by public authorities. The location and connectivity of the area of emergence are very important. 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, China is prone to risks. It has become one of the largest manufacturing centers in the world, notably around the Pearl River Delta. This implies intense trade and business transactions, significant migrations of people from different regions of China, and networks of people living in different countries that have kept roots (relatives) in the countryside. Additionally, large international transport terminals, including the largest airports in the world, are in proximity. If the infection jumps immediately at a gateway, the diffusion could be rapid and extensive before being acknowledged as a significant health threat.
- B. 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 international and regional air transport network structure. 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 the translocation will be different depending on the connectivity of where the virus has emerged. Clusters of infection appear, often in unrelated locations from a proximity standpoint. Several health authorities begin to issue warnings and try to assess the scale and scope of the infection. At this point, several segments of the air transport system would likely 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 curtail its advance.
- C. Diffusion. At this point, translocation has brought influenza-like infections in almost every major transport hub of the world. From multiple hubs, the pandemic diffuses in a more standard fashion linked through proximity and slower land transport systems (rail, road, public transit); often referred to as community spread. From a pandemic control standpoint, it is essentially too late to do anything since its extent is global, and many 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 as leisure) are starting to shut down, either through decree or voluntarily (more likely). The main goal is to impose measures that slow the spread of the disease so that medical systems are not overwhelmed, and that supply chains can continue to operate.
- D. Pandemic. At 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 (transit and air travel) slows down to a trickle, and essential freight distributions 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 depend on the virulence and lethality of the pandemic and how the public and private sectors have responded. The outcome could range from benign to serious; from a slowdown followed by a relatively quick recovery to social collapse in large areas caused by food, energy, and medical supply shortages. While the Spanish Flux pandemic (1918-1920) occurred in a world with much lower interdependencies, the Covid-19 (2019-22) pandemic occurred in a globalized economy.