title: Decreased Carriage and Genetic Shifts in the Streptococcus pneumoniae Population After Changing the Seven-valent to the Thirteen-valent Pneumococcal Vaccine in Norway.
abstract: BACKGROUND
  Shifts in the pneumococcal population colonizing healthy children are expected after switching from a 7-valent pneumococcal conjugate vaccine (PCV7) to a 13-valent (PCV13) in the childhood immunization program. We assessed effects of the switch by comparing pneumococcal carriage and serotype and genetic diversity of pneumococci carried by children in the PCV13-era with those carried in the prevaccination-era and PCV7-era.
  
  
  METHODS
  Nasopharyngeal swabs were obtained in autumn 2013 from children attending day-care centers (874 swabs, 583 isolates). Serotyping, multilocus sequence typing and antimicrobial susceptibility testing were performed on all isolates. Results were compared with samples from 2006 (610 swabs, 538 isolates) and 2008 (600 swabs, 562 isolates).
  
  
  RESULTS
  The carriage prevalence in 2013 was 62 of 100 children (95% confidence intervals: 58-66), a significant decrease from 2006 and 2008. PCV13 serotypes accounted for 7% of isolates in 2013. Non-PCV13 prevalence increased from 2006 to 2008 [prevalence ratio: 1.73 (1.40-2.15)] but remained stable in 2013 [0.99 (0.88-1.12)]. Still, non-PCV13 serotypes 21, 23B, 23A and 22F had increased. In 2013, the serotype and genetic diversity had decreased slightly, and distinct serotype and genetic profiles clustered more within day-care centers compared with the earlier samples. Serotype switch was uncommon. Overall, antimicrobial resistance was limited.
  
  
  CONCLUSIONS
  Carriage of PCV13 serotypes has decreased without a coinciding increase in non-PCV13 serotypes. The serotype and genetic shifts among non-PCV13 serotypes suggest that a new equilibrium has not yet been reached. As the few non-PCV13 serotypes that increased have generally a lower invasive capacity than vaccine serotypes, direct and indirect protection of PCV13 on invasive pneumococcal disease can be expected to continue.
authors.affiliation: From the *Division of Infectious Disease Control, Department of Bacteriology and Immunology, Norwegian Institute of Public Health, Oslo, Norway; †Faculty of Medicine, University of Oslo, Oslo, Norway; and ‡European Programme for Public Health Microbiology Training (EUPHEM), European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden.
authors.forename: Anneke
authors.initials: A
authors.lastname: Steens
authors.forename: Dominique A
authors.initials: DA
authors.lastname: Caugant
authors.forename: Ingeborg S
authors.initials: IS
authors.lastname: Aaberge
authors.forename: Didrik F
authors.initials: DF
authors.lastname: Vestrheim
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002353:Carrier State / Q000453:epidemiology / Q000276:immunology / Q000382:microbiology*; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D024881:Drug Resistance, Bacterial; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008826:Microbial Sensitivity Tests; D058885:Multilocus Sequence Typing; D009664:Norway / Q000453:epidemiology; D011008:Pneumococcal Infections / Q000453:epidemiology / Q000276:immunology / Q000382:microbiology*; D022242:Pneumococcal Vaccines / Q000276:immunology*; D013296:Streptococcus pneumoniae / Q000187:drug effects / Q000235:genetics* / Q000276:immunology
chemical_list: D000900:Anti-Bacterial Agents; D022242:Pneumococcal Vaccines