Regional COVID-19 spread despite expected declines: how mitigation is hindered by spatio-temporal variation in local control measures.


Successful public health regimes for COVID-19 push below unity long-term global Rt — the average number of secondary cases caused by an infectious individual. Most assessments use local information. Populations differ in Rt, amongst themselves and over time. We use a SIR model for two populations to make the conceptual point that even if each locality averages Rt < 1, the overall epidemic can still grow, provided these populations have asynchronous variation in transmission, and are coupled by movement of infectious individuals. This emergent effect in pandemic dynamics instantiates “Parrondo’s Paradox,” — an entity comprised of distinct but interacting units can behave qualitatively differently than each part on its own. For effective COVID-19 disease mitigation strategies, it is critical that infectious individuals moving among locations be identified and quarantined. This does not warrant indiscriminate prevention of movement, but rather rational, targeted testing and national coordination.

Competing Interest Statement

The authors have declared no competing interest.

Clinical Trial

Not applicable (no clinical trials)

Funding Statement

This work was funded (via support of postdoctoral salaries) by USDA (award number 2017-67013-26870) as part of the joint USDA-NSF-NIH Ecology and Evolution of Infectious Diseases program, the National Science Foundation (DEB-1655555), and the University of Florida Foundation.

Author Declarations

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.


The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The research is a modeling study, which did not require IRB/oversight body approval.

All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived.


I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).


I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.


Data Availability

The manuscript is a modeling story, all parameters used in the model are drawn from papers cited in the manuscript.

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