When it comes to infectious disease outbreaks, cities are dual-edged. To be sure, cities are a big part of the problem. They intensify the spread and transmission of infectious disease through increased human contact. Today, roughly 4 billion people live in cities, more than half of the world’s population. According to some analysts, around 600 cities generate two thirds of global GDP. Precisely because they are hubs for transnational commerce and mobility, densely populated and hyper-connected cities can amplify pandemic risk.

It is not just ‘global cities’ that are a risk of SARS, H1N1 or COVID-19, but also secondary cities and other urban hubs as well. Scholars have found that pandemics often emerge from the edge of cities. Viral outbreaks are frequently incubated and transmitted via peri-urban communities and transportation corridors at the outskirts of cities before they spread into the downtown core. It is not just cities, but also their local and global supply chains, travel networks, airports and specific neighborhoods that are sources of contagion.