  The ongoing SARS-CoV-2 pandemic has been holding the world hostage for more
than a year now. Mobility is key to viral spreading and its restriction is the
main non-pharmaceutical interventions to fight the virus expansion. Previous
works have shown a connection between the structural organization of cities and
the movement patterns of their residents. This puts urban centers in the focus
of epidemic surveillance and interventions. Here we show that the organization
of urban flows has a tremendous impact on disease spreading and on the
amenability of different mitigation strategies. By studying anonymous and
aggregated intra-urban flows in a variety of cities in the United States and
other countries, and a combination of empirical analysis and analytical
methods, we demonstrate that the response of cities to epidemic spreading can
be roughly classified in two major types according to the overall organization
of those flows. Hierarchical cities, where flows are concentrated primarily
between mobility hotspots, are particularly vulnerable to the rapid spread of
epidemics. Nevertheless, mobility restrictions in such types of cities are very
effective in mitigating the spread of a virus. Conversely, in sprawled cities
which present many centers of activity, the spread of an epidemic is much
slower, but the response to mobility restrictions is much weaker and less
effective. Investing resources on early monitoring and prompt ad-hoc
interventions in more vulnerable cities may prove helpful in containing and
reducing the impact of future pandemics.
