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Thompson K.M.,Kid Risk Inc.
Risk Analysis | Year: 2013

This introduction to the special issue on modeling poliovirus risks provides context about historical efforts to manage polioviruses and reviews the insights from models developed to support risk management and policy development. Following an overview of the contents of the special issue, the introduction explores the road ahead and offers perspective on the legacy of polio eradication. © 2013 Society for Risk Analysis. Source


Duintjer Tebbens R.J.,Kid Risk Inc. | Pallansch M.A.,Centers for Disease Control and Prevention | Thompson K.M.,Kid Risk Inc.
BMC Infectious Diseases | Year: 2015

Background: A small number of individuals with B-cell-related primary immunodeficiency diseases (PIDs) may exhibit long-term (prolonged or chronic) excretion of immunodeficiency-associated vaccine-derived polioviruses (iVDPVs) following infection with oral poliovirus vaccine (OPV). These individuals pose a risk of live poliovirus reintroduction into the population after global wild poliovirus eradication and subsequent OPV cessation. Treatment with polio antiviral drugs may potentially stop excretion in some of these individuals and thus may reduce the future population risk. Methods: We developed a discrete event simulation model to characterize the global prevalence of long-term iVDPV excretors based on the best available evidence. We explored the impact of different assumptions about the effectiveness of polio antiviral drugs and the fraction of long-term excretors identified and treated. Results: Due to the rarity of long-term iVDPV excretion and limited data on the survival of PID patients in developing countries, uncertainty remains about the current and future prevalence of long-term iVDPV excretors. While the model suggests only approximately 30 current excretors globally and a rapid decrease after OPV cessation, most of these excrete asymptomatically and remain undetected. The possibility that one or more PID patients may continue to excrete iVDPVs for several years after OPV cessation represents a risk for reintroduction of live polioviruses after OPV cessation, particularly for middle-income countries. With the effectiveness of a single polio antiviral drug possibly as low as 40% and no system in place to identify and treat asymptomatic excretors, the impact of passive use of a single polio antiviral drug to treat identified excretors appears limited. Higher drug effectiveness and active efforts to identify long-term excretors will dramatically increase the benefits of polio antiviral drugs. Conclusions: Efforts to develop a second polio antiviral compound to increase polio antiviral effectiveness and/or to maximize the identification and treatment of affected individuals represent important risk management opportunities for the polio endgame. Better data on the survival of PIDpatients in developing countries and more longitudinal data on their exposure to and recovery from OPV infections would improve our understanding of the risks associated with iVDPV excretors and the benefits of further investments in polio antiviral drugs. © 2015 Duintjer Tebbens et al. Source


Kalkowska D.A.,Kid Risk Inc. | Kalkowska D.A.,Technical University of Delft | Duintjer Tebbens R.J.,Kid Risk Inc. | Thompson K.M.,Kid Risk Inc.
American Journal of Epidemiology | Year: 2012

The Global Polio Laboratory Network maintains active surveillance for circulating live polioviruses by obtaining and testing stool samples from patients with acute flaccid paralysis. However, most poliovirus infections occur with no symptoms, and questions remain about the probability of undetected wild poliovirus (WPV) circulation after the apparent interruption of WPV transmission in different populations. In the context of making decisions about the timing of oral poliovirus vaccine cessation following global eradication of WPV, policy-makers need an understanding of this probability as a function of time. Prior modeling of the probability of undetected circulation relied on relatively simple models and assumptions, which limits extrapolation to current conditions. In this analysis, the authors revisit the topic and highlight important considerations for policy-makers related to the impact of initial conditions and seasonality and emphasize the need to focus on appropriate characterization of conditions in the last likely reservoirs of the virus. The authors conclude that the probability of undetected WPV circulation may vary significantly for different poliovirus serotypes, places, and conditions, which suggests that achieving the same level of confidence about the true interruption of WPV transmission will require different periods of time for different situations. © 2012 The Auther. Source


Thompson K.M.,Kid Risk Inc. | Thompson K.M.,University of Central Florida | Tebbens R.J.D.,Kid Risk Inc.
Journal of Infectious Diseases | Year: 2014

Background: Oral poliovirus vaccine (OPV) results in an ongoing burden of poliomyelitis due to vaccine-associated paralytic poliomyelitis and circulating vaccine-derived polioviruses (cVDPVs). This motivates globally coordinated OPV cessation after wild poliovirus eradication.Methods: We modeled poliovirus transmission and OPV evolution to characterize the interaction between population immunity, OPV-related virus prevalence, and the emergence of cVDPVs after OPV cessation. We explored strategies to prevent and manage cVDPVs for countries that currently use OPV for immunization and characterized cVDPV emergence risks and OPV use for outbreak response.Results: Continued intense supplemental immunization activities until OPV cessation represent the best strategy to prevent cVDPV emergence after OPV cessation in areas with insufficient routine immunization coverage. Policy makers must actively manage population immunity before OPV cessation to prevent cVDPVs and aggressively respond if prevention fails. Sufficiently aggressive response with OPV to interrupt transmission of the cVDPV outbreak virus will lead to die-out of OPV-related viruses used for response in the outbreak population. Further analyses should consider the risk of exportation to other populations of the outbreak virus and any OPV used for outbreak response.Conclusions: OPV cessation can successfully eliminate all circulating live polioviruses in a population. The polio end game requires active risk management. © The Author 2014. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. © 2014 Published by Oxford University Press on behalf of the Infectious Diseases Society of America 2014. This work is written by (a) US Government employee(s) and is in the public domain in the US. Source


Thompson K.M.,Kid Risk Inc. | Duintjer Tebbens R.J.,Kid Risk Inc.
BMC Infectious Diseases | Year: 2015

Background: World leaders remain committed to globally-coordinated oral poliovirus vaccine (OPV) cessation following successful eradication of wild polioviruses, but the best timing and strategy for implementation depend on existing and emerging conditions. Methods: Using an existing integrated global poliovirus risk management model, we explore alternatives to the current timing plan of coordinated cessation of each OPV serotype (i.e., OPV1, OPV2, and OPV3 cessation for serotypes 1, 2, and 3, respectively). We assume the current timing plan involves OPV2 cessation in 2016 followed by OPV1 and OPV3 cessation in 2019 and we compare this to alternative timing options, including cessation of all three serotypes in 2018 or 2019, and cessation of both OPV2 and OPV3 in 2017 followed by OPV1 in 2019. Results: If Supplemtal Immunization Activity frequency remains sufficiently high through cessation of the last OPV serotype, then all OPV cessation timing options prevent circulating vaccine-derived poliovirus (cVDPV) outbreaks after OPV cessation of any serotype. The various OPV cessation timing options result in relatively modest differences in expected vaccine-associated paralytic poliomyelitis cases and expected total of approximately 10-13 billion polio vaccine doses used. However, the expected amounts of vaccine of different OPV formulations needed changes dramatically with each OPV cessation timing option. Overall health economic impacts remain limited for timing options that only change the OPV formulation but preserve the currently planned year for cessation of the last OPV serotype and the global introduction of inactivated poliovirus vaccine (IPV) introduction. Earlier cessation of the last OPV serotype or later global IPV introduction yield approximately $1 billion in incremental net benefits due to saved vaccination costs, although the logistics of implementation of OPV cessation remain uncertain and challenging. Conclusions: All countries should maintain the highest possible levels of population immunity to transmission for each poliovirus serotype prior to the coordinated cessation of the OPV serotype to manage cVDPV risks. If OPV2 cessation gets delayed, then global health leaders should consider other OPV cessation timing options. © 2015 Thompson and Duintjer Tebbens. Source

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