title: Declining serotype coverage of new pneumococcal conjugate vaccines relating to the carriage of Streptococcus pneumoniae in young children.
abstract: BACKGROUND
  Asymptomatic carriage of the opportunistic pathogen Streptococcus pneumoniae is known to precede the development of invasive disease. Young children are one of the major reservoirs for pneumococci and worldwide over 700,000 children under two years old die due to invasive pneumococcal disease each year. Heptavalent conjugate vaccine (PCV-7) was introduced into the UK childhood immunisation schedule in September 2006. Our objective was to assess the emergence of colonising serotypes in young children in the three years following PCV-7 implementation.
  
  
  METHODS
  Time-series prevalence survey set in the paediatric outpatients department of a large UK teaching hospital. Participants were children aged four years and under attending the outpatients department during PCV-7 introduction (October 2006-February 2007) and in the same months of the two subsequent years. The main outcome measure was prevalence of pneumococcal carriage by serotype.
  
  
  RESULTS
  The rate of pneumococcal nasopharyngeal carriage remained stable during the three year period. We observed a significant 69% (95% CI, -40% to -118%, p<0.0001) decrease in carriage of PCV-7 serotypes during PCV-7 implementation and a concomitant increase in the proportion of non PCV-7 serotypes. The most prevalent emerging non-vaccine serotypes were 6C, 11A, 19A and 22F. By March 2009, PCV-13 was predicted to cover only 33.3% (95% CI, 24.2-42.5%) of strains carried in the study population.
  
  
  CONCLUSIONS
  Although the overall pneumococcal carriage rate remained stable between 2006 and 2009, we observed a significant decrease in the serotype coverage of PCV-7 and PCV-13. PCV-7 was highly successful in reducing carriage of vaccine serotypes. However, the increase in the proportion of non-vaccine serotypes found both in our study and causing invasive disease currently in the UK, underlines the importance of continued surveillance of carriage and disease.
authors.affiliation: Division of Infection, Inflammation and Immunity, University of Southampton, School of Medicine, Southampton, UK.
authors.forename: Anna S
authors.initials: AS
authors.lastname: Tocheva
authors.forename: Johanna M C
authors.initials: JM
authors.lastname: Jefferies
authors.forename: Henry
authors.initials: H
authors.lastname: Rubery
authors.forename: Jessica
authors.initials: J
authors.lastname: Bennett
authors.forename: Geraldine
authors.initials: G
authors.lastname: Afimeke
authors.forename: Joanna
authors.initials: J
authors.lastname: Garland
authors.forename: Myron
authors.initials: M
authors.lastname: Christodoulides
authors.forename: Saul N
authors.initials: SN
authors.lastname: Faust
authors.forename: Stuart C
authors.initials: SC
authors.lastname: Clarke
mesh_terms: D002353:Carrier State / Q000453:epidemiology* / Q000276:immunology / Q000382:microbiology / Q000517:prevention & control; D002675:Child, Preschool; D006801:Humans; D009305:Nasopharynx / Q000382:microbiology; D011008:Pneumococcal Infections / Q000453:epidemiology* / Q000276:immunology / Q000382:microbiology / Q000517:prevention & control; D022242:Pneumococcal Vaccines / Q000008:administration & dosage* / Q000276:immunology; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification* / Q000276:immunology / Q000302:isolation & purification; D014611:Vaccination / Q000706:statistics & numerical data; D018074:Vaccines, Conjugate / Q000008:administration & dosage* / Q000276:immunology
chemical_list: D022242:Pneumococcal Vaccines; D018074:Vaccines, Conjugate