title: Population effect of 10-valent pneumococcal conjugate vaccine on nasopharyngeal carriage of Streptococcus pneumoniae and non-typeable Haemophilus influenzae in Kilifi, Kenya: findings from cross-sectional carriage studies.
abstract: BACKGROUND
  The effect of 7-valent pneumococcal conjugate vaccine (PCV) in developed countries was enhanced by indirect protection of unvaccinated individuals, mediated by reduced nasopharyngeal carriage of vaccine-serotype pneumococci. The potential indirect protection of 10-valent PCV (PCV10) in a developing country setting is unknown. We sought to estimate the effectiveness of introduction of PCV10 in Kenya against carriage of vaccine serotypes and its effect on other bacteria.
  
  
  METHODS
  PCV10 was introduced into the infant vaccination programme in Kenya in January, 2011, accompanied by a catch-up campaign in Kilifi County for children aged younger than 5 years. We did annual cross-sectional carriage studies among an age-stratified, random population sample in the 2 years before and 2 years after PCV10 introduction. A nasopharyngeal rayon swab specimen was collected from each participant and was processed in accordance with WHO recommendations. Prevalence ratios of carriage before and after introduction of PCV10 were calculated by log-binomial regression.
  
  
  RESULTS
  About 500 individuals were enrolled each year (total n=2031). Among children younger than 5 years, the baseline (2009-10) carriage prevalence was 34% for vaccine-serotype Streptococcus pneumoniae, 41% for non-vaccine-serotype Streptococcus pneumoniae, and 54% for non-typeable Haemophilus influenzae. After PCV10 introduction (2011-12), these percentages were 13%, 57%, and 40%, respectively. Adjusted prevalence ratios were 0·36 (95% CI 0·26-0·51), 1·37 (1·13-1·65), and 0·62 (0·52-0·75), respectively. Among individuals aged 5 years or older, the adjusted prevalence ratios for vaccine-serotype and non-vaccine-serotype S pneumoniae carriage were 0·34 (95% CI 0·18-0·62) and 1·13 (0·92-1·38), respectively. There was no change in prevalence ratio for Staphylococcus aureus (adjusted prevalence ratio for those <5 years old 1·02, 95% CI 0·52-1·99, and for those ≥5 years old 0·90, 0·60-1·35).
  
  
  CONCLUSIONS
  After programmatic use of PCV10 in Kilifi, carriage of vaccine serotypes was reduced by two-thirds both in children younger than 5 years and in older individuals. These findings suggest that PCV10 introduction in Africa will have substantial indirect effects on invasive pneumococcal disease.
  
  
  BACKGROUND
  GAVI Alliance and Wellcome Trust.
authors.affiliation: Kenya Medical Research Institute-Wellcome Trust Research Programme, Kilifi, Kenya; Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA. Electronic address: lhammitt@jhsph.edu.
authors.forename: Laura L
authors.initials: LL
authors.lastname: Hammitt
authors.affiliation: Kenya Medical Research Institute-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Donald O
authors.initials: DO
authors.lastname: Akech
authors.affiliation: Kenya Medical Research Institute-Wellcome Trust Research Programme, Kilifi, Kenya; Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK.
authors.forename: Susan C
authors.initials: SC
authors.lastname: Morpeth
authors.affiliation: Kenya Medical Research Institute-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Angela
authors.initials: A
authors.lastname: Karani
authors.affiliation: Kenya Medical Research Institute-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Norbert
authors.initials: N
authors.lastname: Kihuha
authors.affiliation: Kenya Medical Research Institute-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Sammy
authors.initials: S
authors.lastname: Nyongesa
authors.affiliation: Kenya Medical Research Institute-Wellcome Trust Research Programme, Kilifi, Kenya; Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK.
authors.forename: Tahreni
authors.initials: T
authors.lastname: Bwanaali
authors.affiliation: Kenya Ministry of Health, Kilifi, Kenya.
authors.forename: Edward
authors.initials: E
authors.lastname: Mumbo
authors.affiliation: Kenya Ministry of Health, Nairobi, Kenya.
authors.forename: Tatu
authors.initials: T
authors.lastname: Kamau
authors.affiliation: Kenya Ministry of Health, Nairobi, Kenya.
authors.forename: Shahnaaz K
authors.initials: SK
authors.lastname: Sharif
authors.affiliation: Kenya Medical Research Institute-Wellcome Trust Research Programme, Kilifi, Kenya; Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK; London School of Hygiene & Tropical Medicine, London, UK.
authors.forename: J Anthony G
authors.initials: JA
authors.lastname: Scott
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D002353:Carrier State / Q000276:immunology* / Q000517:prevention & control; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D003906:Developing Countries; D005260:Female; D006193:Haemophilus influenzae / Q000187:drug effects / Q000276:immunology*; D006801:Humans; D017589:Immunization Programs / Q000379:methods / Q000706:statistics & numerical data; D007223:Infant; D007630:Kenya; D008297:Male; D008875:Middle Aged; D009305:Nasopharynx / Q000187:drug effects / Q000276:immunology*; D011008:Pneumococcal Infections / Q000276:immunology / Q000517:prevention & control; D022242:Pneumococcal Vaccines / Q000276:immunology*; D011159:Population Surveillance / Q000379:methods*; D013296:Streptococcus pneumoniae / Q000187:drug effects / Q000276:immunology*; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: C586648:10-valent pneumococcal conjugate vaccine; D022242:Pneumococcal Vaccines
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