title: The role of older children and adults in wild poliovirus transmission.
abstract: As polio eradication inches closer, the absence of poliovirus circulation in most of the world and imperfect vaccination coverage are resulting in immunity gaps and polio outbreaks affecting adults. Furthermore, imperfect, waning intestinal immunity among older children and adults permits reinfection and poliovirus shedding, prompting calls to extend the age range of vaccination campaigns even in the absence of cases in these age groups. The success of such a strategy depends on the contribution to poliovirus transmission by older ages, which has not previously been estimated. We fit a mathematical model of poliovirus transmission to time series data from two large outbreaks that affected adults (Tajikistan 2010, Republic of Congo 2010) using maximum-likelihood estimation based on iterated particle-filtering methods. In Tajikistan, the contribution of unvaccinated older children and adults to transmission was minimal despite a significant number of cases in these age groups [reproduction number, R = 0.46 (95% confidence interval, 0.42-0.52) for >5-y-olds compared to 2.18 (2.06-2.45) for 0- to 5-y-olds]. In contrast, in the Republic of Congo, the contribution of older children and adults was significant [R = 1.85 (1.83-4.00)], perhaps reflecting sanitary and socioeconomic variables favoring efficient virus transmission. In neither setting was there evidence for a significant role of imperfect intestinal immunity in the transmission of poliovirus. Bringing the immunization response to the Tajikistan outbreak forward by 2 wk would have prevented an additional 130 cases (21%), highlighting the importance of early outbreak detection and response.
authors.affiliation: Medical Research Council Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, United Kingdom; isobel.blake@imperial.ac.uk.
authors.forename: Isobel M
authors.initials: IM
authors.lastname: Blake
authors.affiliation: Regional Office for Europe, World Health Organization, DK-2100 Copenhagen, Denmark;Global Immunization Division, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA 30333;
authors.forename: Rebecca
authors.initials: R
authors.lastname: Martin
authors.affiliation: Polio and Emergencies Cluster, World Health Organization, 1211 Geneva, Switzerland.
authors.forename: Ajay
authors.initials: A
authors.lastname: Goel
authors.affiliation: Global Immunization Division, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA 30333;
authors.forename: Nino
authors.initials: N
authors.lastname: Khetsuriani
authors.affiliation: Polio and Emergencies Cluster, World Health Organization, 1211 Geneva, Switzerland.
authors.forename: Johannes
authors.initials: J
authors.lastname: Everts
authors.affiliation: Polio and Emergencies Cluster, World Health Organization, 1211 Geneva, Switzerland.
authors.forename: Christopher
authors.initials: C
authors.lastname: Wolff
authors.affiliation: Global Immunization Division, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA 30333;
authors.forename: Steven
authors.initials: S
authors.lastname: Wassilak
authors.affiliation: Polio and Emergencies Cluster, World Health Organization, 1211 Geneva, Switzerland.
authors.forename: R Bruce
authors.initials: RB
authors.lastname: Aylward
authors.affiliation: Medical Research Council Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, United Kingdom;
authors.forename: Nicholas C
authors.initials: NC
authors.lastname: Grassly
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D002648:Child; D002675:Child, Preschool; D003223:Congo / Q000453:epidemiology; D004196:Disease Outbreaks / Q000706:statistics & numerical data; D005843:Geography; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008954:Models, Biological; D011051:Poliomyelitis / Q000453:epidemiology / Q000635:transmission* / Q000821:virology*; D017955:Poliovirus / Q000502:physiology*; D013620:Tajikistan / Q000453:epidemiology
keywords: epidemiology; infectious diseases; mathematical modeling