  Mobility restrictions - travel advisories, trade and travel bans, border
closures and, in extreme cases, area quarantines or cordons sanitaires - are
among the most widely used measures to control infectious diseases.
Restrictions of this kind were important in the response to epidemics of SARS
(2003), H1N1 influenza (2009), and Ebola (2014). However, they do not always
work as expected. The imposition of a cordon sanitaire to control the 2014 West
African Ebola outbreak, for example, is argued to have led to a
higher-than-expected number of cases in the quarantined area. To determine when
mobility restrictions reduce the size of an epidemic, we use a model of disease
transmission within and between economically heterogeneous locally connected
communities. One community comprises a low-risk, resource-rich, low-density
population with access to effective medical resources. The other comprises a
high-risk, resource-poor, high-density population without access to effective
medical resources. We find that the overall size of an epidemic centered in the
high-risk community is sensitive to the stringency of mobility restrictions
between the two communities. Unrestricted mobility between the two risk
communities increases the number of secondary cases in the low-risk community
but reduces the overall epidemic size. By contrast, the imposition of a cordon
sanitaire around the high-risk community reduces the number of secondary
infections in the low-risk community but increases the overall epidemic size.
The degree to which mobility restrictions increase or decrease the overall
epidemic size depends on the level of risk in each community and the
characteristics of the disease.
