title: The role of vaccine coverage within social networks in cholera vaccine efficacy.
abstract: BACKGROUND
  Traditional vaccine trial methods have an underlying assumption that the effect of a vaccine is the same throughout the trial area. There are, however, many spatial and behavioral factors that alter the rates of contact among infectious and susceptible individuals and result in different efficacies across a population. We reanalyzed data from a field trial in Bangladesh to ascertain whether there is evidence of indirect protection from cholera vaccines when vaccination rates are high in an individual's social network.
  
  
  METHODS
  We analyzed the first year of surveillance data from a placebo-controlled trial of B subunit-killed whole-cell and killed whole-cell-only oral cholera vaccines in children and adult women in Bangladesh. We calculated whether there was an inverse trend for the relation between the level of vaccine coverage in an individual's social network and the incidence of cholera in individual vaccine recipients or placebo recipients after controlling for potential confounding variables.
  
  
  RESULTS
  Using bari-level social network ties, we found incidence rates of cholera among placebo recipients were inversely related to levels of vaccine coverage (5.28 cases per 1000 in the lowest quintile vs 3.27 cases per 1000 in the highest quintile; p = 0.037 for trend). Receipt of vaccine by an individual and the level of vaccine coverage of the individual's social network were independently related to a reduced risk of cholera.
  
  
  CONCLUSIONS
  Findings indicate that progressively higher levels of vaccine coverage in bari-level social networks can lead to increasing levels of indirect protection of non-vaccinated individuals and could also lead to progressively higher levels of total protection of vaccine recipients.
authors.affiliation: Department of Geography and Institute of Behavioral Sciences, University of Colorado at Boulder, Boulder, Colorado, United States of America. roote@colorado.edu
authors.forename: Elisabeth D
authors.initials: ED
authors.lastname: Root
authors.forename: Sophia
authors.initials: S
authors.lastname: Giebultowicz
authors.forename: Mohammad
authors.initials: M
authors.lastname: Ali
authors.forename: Mohammad
authors.initials: M
authors.lastname: Yunus
authors.forename: Michael
authors.initials: M
authors.lastname: Emch
mesh_terms: D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D001459:Bangladesh; D002648:Child; D002675:Child, Preschool; D002771:Cholera / Q000276:immunology* / Q000517:prevention & control*; D022121:Cholera Vaccines / Q000627:therapeutic use*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D032521:Immunity, Herd; D008137:Longitudinal Studies; D012944:Social Support; D016896:Treatment Outcome; D014611:Vaccination
chemical_list: D022121:Cholera Vaccines