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

ABSTRACT: 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.

SUBMITTER: Kalkowska DA

PROVIDER: S-EPMC7842182 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

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

Kalkowska Dominika A DA Duintjer Tebbens Radboud J RJ Pallansch Mark A MA Thompson Kimberly M KM

Risk analysis : an official publication of the Society for Risk Analysis 20181008 2

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 complex ...[more]

PMID: 30296340

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Project description:BackgroundAfghanistan is one of two countries with endemic wild poliovirus type 1 (WPV1). The oral poliovirus vaccine (OPV) is the predominant vaccine used for polio eradication. Although OPV has been administered in routine childhood immunization and during frequent supplementary immunization activities, WPV1 continues to circulate in Afghanistan and case incidence has been increasing since 2017. We estimated the effectiveness of OPV in Afghanistan during 2010-2020.MethodsWe conducted a matched case-control analysis using acute flaccid paralysis (AFP) surveillance data from 29,370 children < 15 years with AFP onset between January 1, 2010 and December 31, 2020. We matched children with confirmed WPV1 (cases) with children with non-polio AFP (controls) by age at onset of paralysis (+/- 3 months), date of onset of paralysis (+/- 3 months), and province of residence, and compared their reported OPV vaccination history to estimate the effectiveness of OPV in preventing paralysis by WPV1 using conditional logistic regression. To account for changes in OPV formulations provided over the analysis period, we stratified the analysis based on dates of the global switch from trivalent OPV (tOPV) to bivalent OPV (bOPV) in April 2016.ResultsBetween January 1, 2010 and December 31, 2020, there were 329 WPV1 cases in Afghanistan. The per-dose estimated effectiveness of OPV against WPV1 was 19% (95% CI: 15%-22%) and of ≥ 7 doses was 94% (95% CI: 90%-97%). Before the global switch from tOPV to bOPV, the per-dose estimated effectiveness of OPV was 14% (95% CI: 11%-18%) and of ≥ 7 doses was 92% (95% CI: 85%-96%). After the switch, the per-dose estimated effectiveness of OPV against WPV1 was 32% (24%-39%) and of ≥ 7 doses was 96% (95% CI: 90%-99%).DiscussionOPV is highly effective in preventing paralysis by WPV1; these results indicate that continued WPV1 transmission in Afghanistan is due to failure to vaccinate, not failure of the vaccine. Although difficult to implement in parts of country, improving the administration of OPV in routine immunization and supplementary immunization activities will be critical for achieving polio eradication in Afghanistan.

Project description:BackgroundPakistan and Afghanistan are two of the three remaining countries yet to interrupt wild-type poliovirus transmission. The increasing incidence of poliomyelitis in these countries during 2010-11 led the Executive Board of WHO in January, 2012, to declare polio eradication a "programmatic emergency for global public health". We aimed to establish why incidence is rising in these countries despite programme innovations including the introduction of new vaccines.MethodsWe did a matched case-control analysis based on a database of 46,977 children aged 0-14 years with onset of acute flaccid paralysis between Jan 1, 2001, and Dec 31, 2011. The vaccination history of children with poliomyelitis was compared with that of children with acute flaccid paralysis due to other causes to estimate the clinical effectiveness of oral poliovirus vaccines (OPVs) in Afghanistan and Pakistan by conditional logistic regression. We estimated vaccine coverage and serotype-specific vaccine-induced population immunity in children aged 0-2 years and assessed their association with the incidence of poliomyelitis over time in seven regions of Afghanistan and Pakistan.FindingsBetween Jan 1, 2001, and Dec 31, 2011, there were 883 cases of serotype 1 poliomyelitis (710 in Pakistan and 173 in Afghanistan) and 272 cases of poliomyelitis serotype 3 (216 in Pakistan and 56 in Afghanistan). The estimated clinical effectiveness of a dose of trivalent OPV against serotype 1 poliomyelitis was 12·5% (95% CI 5·6-18·8) compared with 34·5% (16·1-48·9) for monovalent OPV (p=0·007) and 23·4% (10·4-34·6) for bivalent OPV (p=0·067). Bivalent OPV was non-inferior compared with monovalent OPV (p=0·21). Vaccination coverage decreased during 2006-11 in the Federally Administered Tribal Areas (FATA), Balochistan, and Khyber Pakhtunkhwa in Pakistan and in southern Afghanistan. Although partially mitigated by the use of more effective vaccines, these decreases in coverage resulted in lower vaccine-induced population immunity to poliovirus serotype 1 in FATA and Balochistan and associated increases in the incidence of poliomyelitis.InterpretationThe effectiveness of bivalent OPV is comparable with monovalent OPV and can therefore be used in eradicating serotype 1 poliomyelitis whilst minimising the risks of serotype 3 outbreaks. However, decreases in vaccination coverage in parts of Pakistan and southern Afghanistan have severely limited the effect of this vaccine.FundingPoliovirus Research subcommittee of WHO, Royal Society, and Medical Research Council.

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

Publications

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

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