title: Modeling undetected live poliovirus circulation after apparent interruption of transmission: implications for surveillance and vaccination.
abstract: BACKGROUND
  Most poliovirus infections occur with no symptoms and this leads to the possibility of silent circulation, which complicates the confirmation of global goals to permanently end poliovirus transmission. Previous simple models based on hypothetical populations assumed perfect detection of symptomatic cases and suggested the need to observe no paralytic cases from wild polioviruses (WPVs) for approximately 3-4 years to achieve 95% confidence about eradication, but the complexities in real populations and the imperfect nature of surveillance require consideration.
  
  
  METHODS
  We revisit the probability of undetected poliovirus circulation using a more comprehensive model that reflects the conditions in a number of places with different characteristics related to WPV transmission, and we model the actual environmental WPV detection that occurred in Israel in 2013. We consider the analogous potential for undetected transmission of circulating vaccine-derived polioviruses. The model explicitly accounts for the impact of different vaccination activities before and after the last detected case of paralytic polio, different levels of surveillance, variability in transmissibility and neurovirulence among serotypes, and the possibility of asymptomatic participation in transmission by previously-vaccinated or infected individuals.
  
  
  RESULTS
  We find that prolonged circulation in the absence of cases and thus undetectable by case-based surveillance may occur if vaccination keeps population immunity close to but not over the threshold required for the interruption of transmission, as may occur in northwestern Nigeria for serotype 2 circulating vaccine-derived poliovirus in the event of insufficient tOPV use. Participation of IPV-vaccinated individuals in asymptomatic fecal-oral transmission may also contribute to extended transmission undetectable by case-based surveillance, as occurred in Israel. We also find that gaps or quality issues in surveillance could significantly reduce confidence about actual disruption. Maintaining high population immunity and high-quality surveillance for several years after the last detected polio cases will remain critical elements of the polio end game.
  
  
  CONCLUSIONS
  Countries will need to maintain vigilance in their surveillance for polioviruses and recognize that their risks of undetected circulation may differ as a function of their efforts to manage population immunity and to identify cases or circulating live polioviruses.
authors.affiliation: Kid Risk, Inc., 10524 Moss Park Road, Site 204-364, Orlando, FL, 32832, USA. d.a.kalkowska@gmail.com.|Delft University of Technology, Delft, Netherlands. d.a.kalkowska@gmail.com.
authors.forename: Dominika A
authors.initials: DA
authors.lastname: Kalkowska
authors.affiliation: Kid Risk, Inc., 10524 Moss Park Road, Site 204-364, Orlando, FL, 32832, USA. rdt@kidrisk.org.
authors.forename: Radboud J
authors.initials: RJ
authors.lastname: Duintjer Tebbens
authors.affiliation: Division of Viral Diseases, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA. map1@cdc.gov.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Pallansch
authors.affiliation: Global Immunization Division, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA, USA. slc1@cdc.gov.
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Cochi
authors.affiliation: Global Immunization Division, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA, USA. sgw1@cdc.gov.
authors.forename: Steven G F
authors.initials: SG
authors.lastname: Wassilak
authors.affiliation: Kid Risk, Inc., 10524 Moss Park Road, Site 204-364, Orlando, FL, 32832, USA. kimt@kidrisk.org.|College of Medicine, University of Central Florida, Orlando, FL, USA. kimt@kidrisk.org.
authors.forename: Kimberly M
authors.initials: KM
authors.lastname: Thompson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D058345:Asymptomatic Infections / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007557:Israel / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009549:Nigeria / Q000453:epidemiology; D011051:Poliomyelitis / Q000175:diagnosis / Q000453:epidemiology / Q000517:prevention & control / Q000635:transmission*; D023321:Poliovirus Vaccines; D062486:Public Health Surveillance / Q000379:methods*; D055815:Young Adult
chemical_list: D023321:Poliovirus Vaccines