title: A decade of herd protection after introduction of meningococcal serogroup C conjugate vaccination.
abstract: BACKGROUND
  Vaccination with meningococcal serogroup C (MenC) conjugate (MCC) polysaccharide vaccines led to a substantial decline in MenC disease in the vaccinated and the unvaccinated population. The decline in the unvaccinated population can be explained by herd protection by reduced colonization of meningococci expressing the MenC capsule. The duration of such herd protection is unknown.
  
  
  METHODS
  In a nationwide study from the Netherlands, we compared MenC invasive disease between 1998 and the introduction of MCC vaccination (2002) with that from 2002 to 2012, in age groups eligible and not eligible for vaccination. The proportions of isolates from clonal complexes with high serogroup C capsule expression rate during carriage (sequence type [ST] 11 and ST-8 complex) was compared between the pre- and postvaccination periods.
  
  
  RESULTS
  A total of 814 patients with invasive MenC disease were included for analysis. There was a 99% decline in MenC disease in patients eligible for vaccination and a 93% decline in those not eligible. Thirty-six percent of the overall MenC reduction between the first and last 4 years of the observation period occurred in the unvaccinated population. Clonal complex was determined in 350 (43%) isolates. The proportion of cases caused by clonal complex ST-11 and ST-8 serogroup C meningococci decreased from 251 of 268 (94%) before, to 46 of 57 (81%) after MCC vaccine introduction (P = .004).
  
  
  CONCLUSIONS
  Our findings provide further evidence that herd protection results from reduced carriage of virulent meningococci. Herd protection was responsible for >36% of MCC vaccine impact and lasted for ≥10 years.
authors: Department of Neurology.
authors: Merijn W
authors: MW
authors: Bijlsma
authors: Department of Neurology.
authors: Matthijs C
authors: MC
authors: Brouwer
authors: Department of Medical Microbiology Netherlands Reference Laboratory for Bacterial Meningitis, Center of Infection and Immunity Amsterdam (CINIMA), Academic Medical Center, University of Amsterdam, The Netherlands.
authors: Lodewijk
authors: L
authors: Spanjaard
authors: Department of Neurology.
authors: Diederik
authors: D
authors: van de Beek
authors: Department of Medical Microbiology Netherlands Reference Laboratory for Bacterial Meningitis, Center of Infection and Immunity Amsterdam (CINIMA), Academic Medical Center, University of Amsterdam, The Netherlands.
authors: Arie
authors: A
authors: van der Ende
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006801:Humans; D032521:Immunity, Herd; D015994:Incidence; D007223:Infant; D008297:Male; D008589:Meningococcal Infections / Q000453:epidemiology* / Q000382:microbiology / Q000517:prevention & control*; D022401:Meningococcal Vaccines / Q000008:administration & dosage / Q000276:immunology*; D008875:Middle Aged; D058885:Multilocus Sequence Typing; D038542:Neisseria meningitidis, Serogroup C / Q000145:classification / Q000235:genetics; D009426:Netherlands / Q000453:epidemiology; D055815:Young Adult
chemical_list: D022401:Meningococcal Vaccines; C410218:serogroup C meningococcal conjugate vaccine
keywords: herd protection; meningococcal infections; serogroup C meningococcal conjugate vaccine