MBI Videos

Workshop 2: Socioepidemiology

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    Matthew Osborne

    Disease and behavior have long been recognized as coupled contagions, and models treating them as such have existed since the mid 2000s. In these models behavior is typically treated as a simple contagion. However, the means of behavior spread may in fact be more complex. We will develop a family of disease-behavior coupled contagion compartmental models in order to examine the effect of behavior contagion type on disease-behavior dynamics. Both a simple and complex behavior contagion model will be investigated, revealing that behavior contagion type can have a significant impact on dynamics. We will also propose a study design for determining how an important health behavior spreads, flu vaccination.

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    Grzegorz Rempala
    Stochastic SIR-type epidemic processes on random graphs are a special class of interaction networks that have become of interest lately for modeling contact-type epidemics (Ebola, HIV, election choices etc). I will discuss a particular case of the SIR epidemic evolving on a configuration model random graph with given degree distribution. In particular, I will describe the relevant large graph limit result which yields the law of large numbers (LLN) for the edge-based SIR process and is useful in building a "network-free" SIR Markov hybrid model for epidemic parameters inference.
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    Joel Miller
    A recent localized outbreak of CVDPV-2 (circulating vaccine-derived Polio virus 2) in Syria caused great concern for the ongoing effort to eradicate Polio. Over 70 children experienced symptoms in a relatively localized geographic region. Given the fact that fewer than 1 in 1000 infected children would be expected to experience symptoms, this suggests a very high attack rate in the region. No cases have been identified since September, and there is (as yet) no evidence that it has spread from the region. A plausible explanation is that lack of vaccination in the region led to a large outbreak which then went extinct, hopefully without seeding other regions. This leads to the possibility that there may be two modes for extinction in a sufficiently isolated community: either high vaccination leading to high immunity, or a large epidemic leading to high immunity. It is plausible that there is an intermediate regime where insufficient vaccination coverage leads to persistence within a community. I will use simulation and analytic models to explore this further. This work is very preliminary and should be interpreted as a speculative attempt to explore scenarios.
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    Eben Kenah
    When integrating epidemiologic data with pathogen phylogenetics, the likelihood for the transmission model is often a branching-process likelihood based on a generation interval distribution. We show that a misspecified likelihood can lead to severely biased estimates with or without a pathogen phylogeny. Writing the likelihood as a survival likelihood with failure times in pairs---a method we call pairwise survival analysis---accounts for time spent at risk of infection. In a simple example with three infections, we show that a pairwise survival likelihood produces more accurate source attribution. In a mass-action model with negligible depletion of susceptibles, the pairwise survival likelihood depends only on information about infected individuals in the limit of a large population. However, this asymptotic likelihood has cumulative hazard terms that have no counterpart in a branching process likelihood. As an example of the flexibility of pairwise survival analysis, we describe a pairwise accelerated failure time model that can be used to estimate covariate effects on infectiousness and susceptibility. This model---modified to account for the buildup of immunity---will be used to estimate the efficacy of the Ebola vaccine based on the WHO ring vaccination trial in Guinea. This trial collected data on individuals exposed to infection who escaped as well as Ebola virus genetic sequences. Finally, we describe a pruning algorithm for calculating an approximate likelihood using both epidemiologic data and a pathogen phylogeny. Pathogen genetics can improve statistical efficiency and reduce bias, but this depends on good epidemiologic study design and a good likelihood for transmission.
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    Matthew Bonds
    Over the past two decades, the global health agenda has increasingly embraced the concept of sustainable development in pursuit of solutions at the “systems� level. A central challenge is that the relevant social, economic, and biophysical systems that influence human health and wellbeing operate at difference spatial and temporal scales and scopes of problem solving. Here, we explore three interconnected self-reinforcing systems of central importance to planetary health: 1) the ecology of poverty, 2) the ecology of disease, and 3) systems of health care delivery. We frame these issues to inform how practical interventions can be implemented and studied to a) create practical systems-level change at the ground level, and b) establish methods for evaluating that change and produce transferable knowledge for scaling or replication.
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    Shweta Bansal
    In high-income countries such as the United States (US), coverage rates for vaccination against vaccine-preventable childhood infections remain high. However, the phenomenon of vaccine hesitancy makes maintenance of herd immunity difficult, impeding global disease eradication efforts. Reaching the ‘last mile’ will require early detection of vaccine refusal (due to philosophical or religious choice), identifying pockets of susceptibility created by underimmunization (due to vaccine unavailability, costs, ineligibility), and determining the factors associated with the behaviors to target strategies to ameliorate the concerns. Towards this goal, we harness high-resolution medical claims data to geographically localize vaccine refusal and underimmunization in the US. Our work represents the first large-scale effort for vaccination behavior surveillance and has the potential to aid in the development of targeted public health strategies for optimizing vaccine uptake globally in high-income settings.
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    Carlos Castillo-Chavez
    Abstract not submitted.
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    John Drake
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    Baltazar Espinoza Cortes, Victor Moreno
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    Ben Althouse

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