Abstract
When a region tries to prevent an outbreak of an epidemic, two broad strategies are available: limiting the inflow of infected cases by using travel restrictions and quarantines or limiting the risk of local transmission from imported cases by using contact tracing and other community interventions. A number of papers have used epidemiological models to argue that inflow restrictions are unlikely to be effective. We simulate a simple epidemiological model to show that this conclusion changes if containment efforts such as contact tracing have limited capacity. In particular, our results show that moderate travel restrictions can lead to large reductions in the probability of an epidemic when contact tracing is effective but the contact tracing system is close to being overwhelmed.
Highlights
Two main factors determine if, and when, a region will be affected by an epidemic like the current COVID-19 outbreak, be it the first epidemic or a second wave after a successful lockdown has eliminated internal spread
Epidemics break out at a rate λπT when the contact tracing system is below capacity and at a rate λπNT > λπT when at capacity
Instead of inflow restrictions leading to a gradual delay of an epidemic, there are nonlinear effects once the system goes below capacity
Summary
Two main factors determine if, and when, a region will be affected by an epidemic like the current COVID-19 outbreak, be it the first epidemic or a second wave after a successful lockdown has eliminated internal spread. Chinazzi et al [2] study the effect of reducing the inflow of infected individuals while simultaneously reducing π in the community at large and find that inflow reductions can only marginally delay an epidemic unless π is reduced drastically. These pessimistic findings mirror those from a large number of earlier models [3,4,5,6,7,8]. If effective contact tracing is not in place, reducing the inflow rate λ will only marginally delay the epidemic, in line with the literature findings above. We think that epidemiological models used for policy analysis should incorporate capacity constraints, since they might otherwise underestimate the potential of travel restrictions to prevent epidemic outbreaks (or the re-emergence of an epidemic)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
