title: Impact of meningococcal serogroup C conjugate vaccines on carriage and herd immunity.
abstract: BACKGROUND
  In 1999, meningococcal serogroup C conjugate (MCC) vaccines were introduced in the United Kingdom for those under 19 years of age. The impact of this intervention on asymptomatic carriage of meningococci was investigated to establish whether serogroup replacement or protection by herd immunity occurred.
  
  
  METHODS
  Multicenter surveys of carriage were conducted during vaccine introduction and on 2 successive years, resulting in a total of 48,309 samples, from which 8599 meningococci were isolated and characterized by genotyping and phenotyping.
  
  
  RESULTS
  A reduction in serogroup C carriage (rate ratio, 0.19) was observed that lasted at least 2 years with no evidence of serogroup replacement. Vaccine efficacy against carriage was 75%, and vaccination had a disproportionate impact on the carriage of sequence type (ST)-11 complex serogroup C meningococci that (rate ratio, 0.06); these meningococci also exhibited high rates of capsule expression.
  
  
  CONCLUSIONS
  The impact of vaccination with MCC vaccine on the prevalence of carriage of group C meningococci was consistent with herd immunity. The high impact on the carriage of ST-11 complex serogroup C could be attributed to high levels of capsule expression. High vaccine efficacy against disease in young children, who were not protected long-term by the schedule initially used, is attributed to the high vaccine efficacy against carriage in older age groups.
authors.affiliation: Dept. of Zoology, John Radcliffe Hospital, Oxford University, Oxford, United Kingdom. martin.maiden@zoo.ox.ac.uk
authors.forename: Martin C J
authors.initials: MC
authors.lastname: Maiden
authors.forename: Ana Belén
authors.initials: AB
authors.lastname: Ibarz-Pavón
authors.forename: Rachel
authors.initials: R
authors.lastname: Urwin
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Gray
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Andrews
authors.forename: Stuart C
authors.initials: SC
authors.lastname: Clarke
authors.forename: A Mark
authors.initials: AM
authors.lastname: Walker
authors.forename: Meirion R
authors.initials: MR
authors.lastname: Evans
authors.forename: J Simon
authors.initials: JS
authors.lastname: Kroll
authors.forename: Keith R
authors.initials: KR
authors.lastname: Neal
authors.forename: Dlawer A A
authors.initials: DA
authors.lastname: Ala'aldeen
authors.forename: Derrick W
authors.initials: DW
authors.lastname: Crook
authors.forename: Kathryn
authors.initials: K
authors.lastname: Cann
authors.forename: Sarah
authors.initials: S
authors.lastname: Harrison
authors.forename: Richard
authors.initials: R
authors.lastname: Cunningham
authors.forename: David
authors.initials: D
authors.lastname: Baxter
authors.forename: Edward
authors.initials: E
authors.lastname: Kaczmarski
authors.forename: Jenny
authors.initials: J
authors.lastname: Maclennan
authors.forename: J Claire
authors.initials: JC
authors.lastname: Cameron
authors.forename: James M
authors.initials: JM
authors.lastname: Stuart
mesh_terms: D000293:Adolescent; D000328:Adult; D002353:Carrier State / Q000453:epidemiology*; D003430:Cross-Sectional Studies; D006801:Humans; D032521:Immunity, Herd / Q000276:immunology*; D032541:Mass Vaccination; D008589:Meningococcal Infections / Q000453:epidemiology* / Q000517:prevention & control; D022401:Meningococcal Vaccines / Q000276:immunology*; D009345:Neisseria meningitidis / Q000145:classification / Q000276:immunology; D038542:Neisseria meningitidis, Serogroup C / Q000276:immunology* / Q000472:pathogenicity; D012703:Serotyping; D006113:United Kingdom / Q000453:epidemiology
chemical_list: D022401:Meningococcal Vaccines; C410218:serogroup C meningococcal conjugate vaccine