Cost-effectiveness of geographically targeted versus ring vaccination campaigns in response to an outbreak of Ebola Virus Disease

For response to an outbreak of Ebola Virus Disease (EVD), the World Health Organisation (WHO) guidelines recommend vaccination of any contacts and contacts-of-contacts of identified EVD cases, also known as ring vaccination. However this standard response can be challenging to implement in remote regions or conflict zones. In recent outbreaks, response efforts have also tried blanket vaccination in the immediate vicinity of the homes and workplaces of identified cases, also known as geographically targeted vaccination. The relative effectiveness of these deployment strategies is difficult to study empirically, and modelling work to date has been limited. In this study, we use a spatially explicit individual-based stochastic simulation to model an EVD epidemic and public health response using either ring or geographically targeted vaccination alongside standard response activities. We explore a wide range of outbreak scenarios and response levels. Overall, we find little difference between ring or geographically targeted vaccination for either health or cost outcomes; the quality of surveillance and effectiveness of standard response activities are much larger drivers. However, vaccination does provide incremental benefit in combination with those activities, and the preferred strategy changes depending how well non-pharmaceutical activities are executed. Ring vaccination provides more incremental benefit on top of otherwise effective response activities (e.g. rapid and high ascertainment of contacts) but geographically targeted vaccination is better when those activities are less effectively delivered. These findings are relevant to policy makers deciding how to most effectively and cost-effectively deploy EVD vaccines in resource-limited and often challenging outbreak settings.