title: Asymptomatic wild-type poliovirus infection in India among children with previous oral poliovirus vaccination.
abstract: BACKGROUND
  Mucosal immunity induced by oral poliovirus vaccine (OPV) is imperfect and potentially allows immunized individuals to participate in asymptomatic wild-type poliovirus transmission in settings with efficient fecal-oral transmission of infection.
  
  
  METHODS
  We examined the extent of asymptomatic wild-type poliovirus transmission in India by measuring the prevalence of virus in stool samples obtained from 14,005 healthy children who were in contact with 2761 individuals with suspected poliomyelitis reported during the period 2003-2008.
  
  
  RESULTS
  Wild-type poliovirus serotypes 1 and 3 were isolated from the stool samples of 103 (0.74%) and 104 (0.74%) healthy contacts, respectively. Among contacts of individuals with laboratory-confirmed poliomyelitis, 27 (12.7%) of 213 and 29 (13.9%) of 209 had serotypes 1 and 3, respectively, isolated from their stool samples. The odds ratio of excreting serotype 1 wild-type poliovirus was 0.13 (95% confidence interval, 0.02-0.87) among healthy children reporting 6 doses of OPV, compared with children reporting 0-2 doses. However, two-thirds of healthy children who excreted this virus reported >or=6 doses, and the prevalence of this virus did not decrease with age over the sampled range.
  
  
  CONCLUSIONS
  Although OPV is protective against infection with poliovirus, the majority of healthy contacts who excreted wild-type poliovirus were well vaccinated. This is consistent with a potential role for OPV-vaccinated children in continued wild-type poliovirus transmission and requires further study.
authors.affiliation: Department of Infectious Disease Epidemiology, Imperial College London, London, United Kingdom. n.grassly@imperial.ac.uk
authors.forename: Nicholas C
authors.initials: NC
authors.lastname: Grassly
authors.forename: Hamid
authors.initials: H
authors.lastname: Jafari
authors.forename: Sunil
authors.initials: S
authors.lastname: Bahl
authors.forename: Sunita
authors.initials: S
authors.lastname: Durrani
authors.forename: Jay
authors.initials: J
authors.lastname: Wenger
authors.forename: Roland W
authors.initials: RW
authors.lastname: Sutter
authors.forename: R
authors.initials: R
authors.lastname: Bruce Aylward
mesh_terms: D002675:Child, Preschool; D005243:Feces / Q000821:virology; D006801:Humans; D007194:India / Q000453:epidemiology; D007223:Infant; D007231:Infant, Newborn; D011051:Poliomyelitis / Q000453:epidemiology / Q000517:prevention & control* / Q000635:transmission / Q000821:virology*; D017955:Poliovirus / Q000145:classification*; D011055:Poliovirus Vaccine, Oral / Q000008:administration & dosage / Q000276:immunology*
chemical_list: D011055:Poliovirus Vaccine, Oral