The probability of undetected wild poliovirus circulation: Can we do better?

Houy, Nicolas

doi:10.1016/j.jtbi.2015.06.046

Cited by 10 publications

(7 citation statements)

References 21 publications

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“…These factors impact the estimates of the probability and duration of undetected LPV circulation in real populations (Kalkowska et al., ). In the context of some hypothetical assumptions about vaccination strategies to achieve elimination in a highly simplified population structure, the date of occurrence of the last paralytic infection also influences the estimates of the risk of declaring WPV eradicated despite ongoing transmission (Houy, ). A recent analysis focused on specific populations that may represent conditions corresponding to the last global reservoirs of WPV transmission (Kalkowska et al., ).…”

Section: Introductionmentioning

confidence: 99%

Modeling Undetected Live Poliovirus Circulation After Apparent Interruption of Transmission: Pakistan and Afghanistan

Kalkowska¹,

Tebbens²,

Pallansch

et al. 2018

Risk Analysis

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Since most poliovirus infections occur with no paralytic symptoms, the possibility of silent circulation complicates the confirmation of the end of poliovirus transmission. Based on empirical field experience and theoretical modeling results, the Global Polio Eradication Initiative identified three years without observing paralytic cases from wild polioviruses with good acute flaccid paralysis surveillance as an indication of sufficient confidence that poliovirus circulation stopped. The complexities of real populations and the imperfect nature of real surveillance systems subsequently demonstrated the importance of specific modeling for areas at high risk of undetected circulation, resulting in varying periods of time required to obtain the same level of confidence about no undetected circulation. Using a poliovirus transmission model that accounts for variability in transmissibility and neurovirulence for different poliovirus serotypes and characterizes country‐specific factors (e.g., vaccination and surveillance activities, demographics) related to wild and vaccine‐derived poliovirus transmission in Pakistan and Afghanistan, we consider the probability of undetected poliovirus circulation for those countries once apparent die‐out occurs (i.e., in the absence of any epidemiological signals). We find that gaps in poliovirus surveillance or reaching elimination with borderline sufficient population immunity could significantly increase the time to reach high confidence about interruption of live poliovirus transmission, such that the path taken to achieve and maintain poliovirus elimination matters. Pakistan and Afghanistan will need to sustain high‐quality surveillance for polioviruses after apparent interruption of transmission and recognize that as efforts to identify cases or circulating live polioviruses decrease, the risks of undetected circulation increase and significantly delay the global polio endgame.

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Section: Introductionmentioning

confidence: 99%

Modeling Undetected Live Poliovirus Circulation After Apparent Interruption of Transmission: Pakistan and Afghanistan

Kalkowska¹,

Tebbens²,

Pallansch

et al. 2018

Risk Analysis

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“…Second, even with that adjustment, as noted above, the TBC metric does not represent the probability of circulation as a function of time without detections, which requires conditioning on the absence of detections. Eichner and Dietz (1996) developed a metric that truly informs the probability of circulation as a function of time without detections, which various other groups subsequently adopted to further address this question (Houy, 2015; Kalkowska, Duintjer Tebbens, Pallansch, et al., 2015). Third, the use of only 1,000 iterations remains insufficient to generate statistically robust findings for the relatively rare events that reflect the tails of highly skewed distributions.…”

Section: Discussionmentioning

confidence: 99%

“…Briefly, Vallejo et al. (2017) explored the model behavior in terms of time between detected cases (TBC), which represents a different metric than those developed in the prior literature (Berchenko et al., 2017; Eichner & Dietz, 1996; Famulare, 2016; Houy, 2015; Kalkowska, Duintjer Tebbens, Pallansch, et al., 2015; Kalkowska et al., 2012). Vallejo et al.…”

Section: Methodsmentioning

confidence: 99%

“…Prior to Vallejo et al. (2017), numerous modeling studies addressed the possibility of prolonged poliovirus circulation without any detected polio cases in different populations using different metrics, and spanning different model structures and assumptions about surveillance, vaccination, transmissibility, and demographics (Berchenko et al., 2017; Eichner & Dietz, 1996; Famulare, 2016; Houy, 2015; Kalkowska, Duintjer Tebbens, Pallansch, et al., 2015; Kalkowska, Duintjer Tebbens, & Thompson, 2012). These models generally agree that in most realistic situations, 3 years without any detected cases implies at least 95% confidence about no circulation, although our studies show that results depend on surveillance quality, serotype, seasonality, and vaccination strategies (Kalkowska, Duintjer Tebbens, Pallansch, et al., 2015; Kalkowska et al., 2012).…”

Section: Introductionmentioning

confidence: 99%

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Another look at silent circulation of poliovirus in small populations

Kalkowska¹,

Tebbens²,

Thompson³

2018

Infectious Disease Modelling

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BackgroundSilent circulation of polioviruses complicates the polio endgame and motivates analyses that explore the probability of undetected circulation for different scenarios. A recent analysis suggested a relatively high probability of unusually long silent circulation of polioviruses in small populations (defined as 10,000 people or smaller).MethodsWe independently replicated the simple, hypothetical model by Vallejo et al. (2017) and repeated their analyses to explore the model behavior, interpretation of the results, and implications of simplifying assumptions.ResultsWe found a similar trend of increasing times between detected cases with increasing basic reproduction number (R0) and population size. However, we found substantially lower estimates of the probability of at least 3 years between successive polio cases than they reported, which appear more consistent with the prior literature. While small and isolated populations may sustain prolonged silent circulation, our reanalysis suggests that the existing rule of thumb of less than a 5% chance of 3 or more years of undetected circulation with perfect surveillance holds for most conditions of the model used by Vallejo et al. and most realistic conditions.ConclusionsAvoiding gaps in surveillance remains critical to declaring wild poliovirus elimination with high confidence as soon as possible after the last detected poliovirus, but concern about transmission in small populations with adequate surveillance should not significantly change the criteria for the certification of wild polioviruses.

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“…A 2012 study25 relaxed some of the assumptions of the prior theoretical model20 and highlighted that the probability of undetected circulation varied for different poliovirus serotypes, places and conditions, which suggested the need to focus on appropriate characterisation of conditions in the last likely WPV reservoirs 25. A 2015 study26 also used the prior model20 to show that in the context of an instantaneous introduction of vaccination, the time of the last case relative to vaccine introduction further informs the confidence about the absence of circulation.…”

Section: Introductionmentioning

confidence: 99%

Global certification of wild poliovirus eradication: insights from modelling hard-to-reach subpopulations and confidence about the absence of transmission

Tebbens¹,

Kalkowska²,

Thompson³

2019

BMJ Open

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ObjectiveTo explore the extent to which undervaccinated subpopulations may influence the confidence about no circulation of wild poliovirus (WPV) after the last detected case.Design and participantsWe used a hypothetical model to examine the extent to which the existence of an undervaccinated subpopulation influences the confidence about no WPV circulation after the last detected case as a function of different characteristics of the subpopulation (eg, size, extent of isolation). We also used the hypothetical population model to inform the bounds on the maximum possible time required to reach high confidence about no circulation in a completely isolated and unvaccinated subpopulation starting either at the endemic equilibrium or with a single infection in an entirely susceptible population.ResultsIt may take over 3 years to reach 95% confidence about no circulation for this hypothetical population despite high surveillance sensitivity and high vaccination coverage in the surrounding general population if: (1) ability to detect cases in the undervaccinated subpopulation remains exceedingly small, (2) the undervaccinated subpopulation remains small and highly isolated from the general population and (3) the coverage in the undervaccinated subpopulation remains very close to the minimum needed to eradicate. Fully-isolated hypothetical populations of 4000 people or less cannot sustain endemic transmission for more than 5 years, with at least 20 000 people required for a 50% chance of at least 5 years of sustained transmission in a population without seasonality that starts at the endemic equilibrium. Notably, however, the population size required for persistent transmission increases significantly for realistic populations that include some vaccination and seasonality and/or that do not begin at the endemic equilibrium.ConclusionsSignificant trade-offs remain inherent in global polio certification decisions, which underscore the need for making and valuing investments to maximise population immunity and surveillance quality in all remaining possible WPV reservoirs.

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The probability of undetected wild poliovirus circulation: Can we do better?

Cited by 10 publications

References 21 publications

Modeling Undetected Live Poliovirus Circulation After Apparent Interruption of Transmission: Pakistan and Afghanistan

Modeling Undetected Live Poliovirus Circulation After Apparent Interruption of Transmission: Pakistan and Afghanistan

Another look at silent circulation of poliovirus in small populations

Global certification of wild poliovirus eradication: insights from modelling hard-to-reach subpopulations and confidence about the absence of transmission

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