title: Effect on nasopharyngeal pneumococcal carriage of replacing PCV7 with PCV13 in the Expanded Programme of Immunization in The Gambia.
abstract: In 2011, two years after the introduction of 7-valent Pneumococcal conjugate vaccine (PCV7), the Gambian immunization programme replaced PVC7 with PCV13 (13-valent). Our objective was to assess the additional impact of PCV13 on prevalence of pneumococcal nasopharyngeal carriage.
  
  
  
  We recruited healthy Gambian infants who had received three PCV doses. Nasopharyngeal swabs were collected from infants and their mothers during two cross-sectional surveys (CSS) conducted in infants vaccinated with PCV7 (CSS1) and vaccinated with PCV13 (CSS2). Pneumococci were isolated and serotyped following standardized methods. Whole genome sequencing was performed on non-typable pneumococcus isolated in CSS1 and CSS2.
  
  
  
  339 and 350 infants and their mothers were recruited in CSS1 and CSS2, respectively. Overall prevalence of pneumococcal carriage was 85.4% in infants. Among infants, prevalence of vaccine type (VT) carriage was lower in CSS2 [9.4% versus 4.9% (p=0.025) for PCV7-VT; 33.3% versus 18.3% (p<0.001) for PCV13-VT and 23.9% versus 13.7% (p=0.001) for the 6 additional serotypes included in PCV13]. At CSS2, there was a decrease of serotypes 6A (from 15.3% to 5.7%, p<0.001) and 19F (from 5.6% to 1.7%, p=0.007), and an increase of non-typable pneumococci (0.3-6.0%, p<0.001), most of which (82.4%) were from typable serotype backgrounds that had lost the ability to express a capsule. Prevalence of overall and VT carriage in mothers was similar in CSS1 and CSS2.
  
  
  
  Replacing PCV7 for PCV13 rapidly decreased prevalence of VT carriage among vaccinated Gambian infants. An indirect effect in mothers was not observed yet. Vaccine-driven selection pressure may have been responsible for the increase of non-typable isolates.
authors.affiliation: Medical Research Council Unit, Fajara, The Gambia; London School of Hygiene & Tropical Medicine, London, United Kingdom. Electronic address: aroca@mrc.gm.
authors.forename: Anna
authors.initials: A
authors.lastname: Roca
authors.affiliation: Medical Research Council Unit, Fajara, The Gambia.
authors.forename: Abdoulie
authors.initials: A
authors.lastname: Bojang
authors.affiliation: London School of Hygiene & Tropical Medicine, London, United Kingdom.
authors.forename: Christian
authors.initials: C
authors.lastname: Bottomley
authors.affiliation: Pathogen Genomics, Wellcome Trust Sanger Institute, Hinxton, Cambridge, United Kingdom.
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Gladstone
authors.affiliation: Medical Research Council Unit, Fajara, The Gambia.
authors.forename: Jane U
authors.initials: JU
authors.lastname: Adetifa
authors.affiliation: Medical Research Council Unit, Fajara, The Gambia.
authors.forename: Uzochukwu
authors.initials: U
authors.lastname: Egere
authors.affiliation: Medical Research Council Unit, Fajara, The Gambia; London School of Hygiene & Tropical Medicine, London, United Kingdom.
authors.forename: Sarah
authors.initials: S
authors.lastname: Burr
authors.affiliation: Medical Research Council Unit, Fajara, The Gambia.
authors.forename: Martin
authors.initials: M
authors.lastname: Antonio
authors.affiliation: Pathogen Genomics, Wellcome Trust Sanger Institute, Hinxton, Cambridge, United Kingdom.
authors.forename: Stephen
authors.initials: S
authors.lastname: Bentley
authors.affiliation: Medical Research Council Unit, Fajara, The Gambia; Department of Paediatrics, Imperial College London, United Kingdom.
authors.forename: Beate
authors.initials: B
authors.lastname: Kampmann
mesh_terms: D000328:Adult; D002353:Carrier State / Q000453:epidemiology / Q000382:microbiology / Q000517:prevention & control*; D003430:Cross-Sectional Studies; D005260:Female; D005714:Gambia / Q000453:epidemiology; D006801:Humans; D007223:Infant; D008297:Male; D009305:Nasopharynx / Q000382:microbiology*; D011008:Pneumococcal Infections / Q000453:epidemiology / Q000382:microbiology / Q000517:prevention & control*; D022242:Pneumococcal Vaccines / Q000008:administration & dosage* / Q000276:immunology; D015995:Prevalence; D017422:Sequence Analysis, DNA; D065288:Serogroup; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*; D055815:Young Adult
chemical_list: C538862:13-valent pneumococcal vaccine; D022242:Pneumococcal Vaccines
keywords: Africa; Epidemiology; Expanded Programme of Immunization; Non-typable; PCV13; PCV7; Vaccine-type