title: Persistent low carriage of serogroup A Neisseria meningitidis two years after mass vaccination with the meningococcal conjugate vaccine, MenAfriVac.
abstract: BACKGROUND
  The conjugate vaccine against serogroup A Neisseria meningitidis (NmA), MenAfriVac, is currently being introduced throughout the African meningitis belt. In repeated multicentre cross-sectional studies in Burkina Faso we demonstrated a significant effect of vaccination on NmA carriage for one year following mass vaccination in 2010. A new multicentre carriage study was performed in October-November 2012, two years after MenAfriVac mass vaccination.
  
  
  METHODS
  Oropharyngeal samples were collected and analysed for presence of N. meningitidis (Nm) from a representative selection of 1-29-year-olds in three districts in Burkina Faso using the same procedures as in previous years. Characterization of Nm isolates included serogrouping, multilocus sequence typing, and porA and fetA sequencing. A small sample of invasive isolates collected during the epidemic season of 2012 through the national surveillance system were also analysed.
  
  
  RESULTS
  From a total of 4964 oropharyngeal samples, overall meningococcal carriage prevalence was 7.86%. NmA prevalence was 0.02% (1 carrier), significantly lower (OR, 0.05, P = 0.005, 95% CI, 0.006-0.403) than pre-vaccination prevalence (0.39%). The single NmA isolate was sequence type (ST)-7, P1.20,9;F3-1, a clone last identified in Burkina Faso in 2003. Nm serogroup W (NmW) dominated with a carriage prevalence of 6.85%, representing 87.2% of the isolates. Of 161 NmW isolates characterized by molecular techniques, 94% belonged to the ST-11 clonal complex and 6% to the ST-175 complex. Nm serogroup X (NmX) was carried by 0.60% of the participants and ST-181 accounted for 97% of the NmX isolates. Carriage prevalence of serogroup Y and non-groupable Nm was 0.20% and 0.18%, respectively. Among the 20 isolates recovered from meningitis cases, NmW dominated (70%), followed by NmX (25%). ST-2859, the only ST with a serogroup A capsule found in Burkina Faso since 2004, was not found with another capsule, neither among carriage nor invasive isolates.
  
  
  CONCLUSIONS
  The significant reduction of NmA carriage still persisted two years following MenAfriVac vaccination, and no cases of NmA meningitis were recorded. High carriage prevalence of NmW ST-11 was consistent with the many cases of NmW meningitis in the epidemic season of 2012 and the high proportion of NmW ST-11 among the characterized invasive isolates.
authors.affiliation: WHO Collaborating Center for Reference and Research on Meningococci, Norwegian Institute of Public Health, Oslo, Norway. paul.kristiansen@fhi.no.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Kristiansen
authors.affiliation: Laboratoire National de Santé Public, Ouagadougou, Burkina Faso. absetou@yahoo.fr.
authors.forename: Absatou Ky
authors.initials: AK
authors.lastname: Ba
authors.affiliation: Centre Hospitalier Universitaire Souro Sanou, Bobo-Dioulasso, Burkina Faso. abdousal2000@yahoo.fr.
authors.forename: Abdoul-Salam
authors.initials: AS
authors.lastname: Ouédraogo
authors.affiliation: Centre Hospitalier Universitaire Souro Sanou, Bobo-Dioulasso, Burkina Faso. idrissasanou@yahoo.com.|Centre Hospitalier Universitaire Yalgado, Ouagadougou, Burkina Faso. idrissasanou@yahoo.com.
authors.forename: Idrissa
authors.initials: I
authors.lastname: Sanou
authors.affiliation: Centre Hospitalier Universitaire Pédiatrique Charles de Gaulle, Ouagadougou, Burkina Faso. ramaouedtra@yahoo.fr.
authors.forename: Rasmata
authors.initials: R
authors.lastname: Ouédraogo
authors.affiliation: Centre Hospitalier Universitaire Yalgado, Ouagadougou, Burkina Faso. sangarel@hotmail.com.
authors.forename: Lassana
authors.initials: L
authors.lastname: Sangaré
authors.affiliation: WHO Inter Country Support Team, Ouagadougou, Burkina Faso. diomandef@who.int.|Centers for Disease Control and Prevention, Atlanta, USA. diomandef@who.int.
authors.forename: Fabien
authors.initials: F
authors.lastname: Diomandé
authors.affiliation: WHO Inter Country Support Team, Ouagadougou, Burkina Faso. kandolokakongod@who.int.
authors.forename: Denis
authors.initials: D
authors.lastname: Kandolo
authors.affiliation: WHO Collaborating Center for Reference and Research on Meningococci, Norwegian Institute of Public Health, Oslo, Norway. inger.marie.saga@fhi.no.
authors.forename: Inger Marie
authors.initials: IM
authors.lastname: Saga
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, USA. are9@cdc.gov.
authors.forename: Lara
authors.initials: L
authors.lastname: Misegades
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, USA. tnc4@cdc.gov.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Clark
authors.affiliation: Meningitis Vaccine Project, Ferney, France. preziosim@who.int.|WHO Initiative for Vaccine Research, Geneva, Switzerland. preziosim@who.int.
authors.forename: Marie-Pierre
authors.initials: MP
authors.lastname: Préziosi
authors.affiliation: WHO Collaborating Center for Reference and Research on Meningococci, Norwegian Institute of Public Health, Oslo, Norway. dominique.caugant@fhi.no.|Faculty of Medicine, University of Oslo, Oslo, Norway. dominique.caugant@fhi.no.
authors.forename: Dominique A
authors.initials: DA
authors.lastname: Caugant
mesh_terms: D000293:Adolescent; D000328:Adult; D058345:Asymptomatic Infections / Q000453:epidemiology; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics; D002050:Burkina Faso / Q000453:epidemiology; D002353:Carrier State / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D032541:Mass Vaccination; D008585:Meningitis, Meningococcal / Q000453:epidemiology; D008589:Meningococcal Infections / Q000453:epidemiology* / Q000517:prevention & control; D022401:Meningococcal Vaccines / Q000627:therapeutic use*; D058885:Multilocus Sequence Typing; D038381:Neisseria meningitidis, Serogroup A / Q000235:genetics / Q000302:isolation & purification*; D009960:Oropharynx / Q000382:microbiology; D018272:Porins / Q000235:genetics; D015995:Prevalence; D014611:Vaccination; D055815:Young Adult
chemical_list: D001425:Bacterial Outer Membrane Proteins; C093120:FrpB protein, bacteria; C573970:MenAfriVac; D022401:Meningococcal Vaccines; D018272:Porins; C057699:porin protein, Neisseria