Calendar Details

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Friday, March 08

Integrating the Effects of Space, Environment, and
Social Networks in a Phase III Oral Cholera Vaccine Trial

Michael Emch, University of North Carolina, Chapel Hill
Geographic Information Science and Technology Group Seminar
10:30 AM — 11:30 AM, Research Office Building (5700), Room L-204
Contact: Budhendra Bhaduri (, 865.241.9272


Geographic heterogeneity in vaccine uptake can alter estimates of protective efficacy through analogous variations in vaccine herd protection. The goal of this study was to determine how geographic factors, along with environmental and social ties among vaccinated and unvaccinated individuals can influence indirect protection of unvaccinated individuals. Using data from a randomized cholera vaccine trial conducted between 1985-88 in Matlab, Bangladesh, we sought to determine how incidence among unvaccinated individuals varied according to social and environmental ties to vaccinated individuals across space. We addressed the impacts of social and environmental connectivity on incidence of non-vaccinees, while also accounting for spatial correlation of incidence, through a logistic model within a Bayesian hierarchical framework. We evaluated the support of competing models associated with environmental, social, and spatial effects using the deviance information criterion (DIC). We found that the best supported model incorporated environmental factors and spatial structure, suggesting that spatial and environmental processes are more important than social processes in predicting the incidence of cholera among non-vaccinees. Through this analysis we provide a unified framework to demonstrate how variation in spatial, environmental, and social processes can contribute to heterogeneity of post-baseline infection risk among unvaccinated individuals in vaccine trials.

About the Speaker:

Dr. Michael Emch is Professor of Geography, Fellow at the Carolina Population Center, and Professor of Epidemiology at the University of North Carolina at Chapel Hill. His expertise is in infectious disease ecology, neighborhood determinants of health, and geographic information science applications of public health. He leads the Spatial Health Research Group which conducts research that explores spatio-temporal patterns of disease, primarily infectious diseases of the developing world. Disease patterns are studied using a holistic approach by investigating the role of natural, social, and built environments in disease occurrence in different places and populations. Diverse statistical and spatial analytical methods are informed by theory from the fields of medical geography, epidemiology, ecology, and others. These theories and methods are used to examine diverse topics such as the role of population-environment drivers in viral evolution, how social connectivity contributes to disease incidence, and using environmental indicators to predict disease outbreaks. One study that he is presently conducting investigates population level drivers of HIV resistance. It integrates spatial analytical and molecular approaches. For more information see the Spatial Health Research Group website at