title: Competition between Streptococcus pneumoniae strains: implications for vaccine-induced replacement in colonization and disease.
abstract: BACKGROUND
  Vaccine-induced replacement by nonvaccine serotypes in pneumococcal colonization and disease poses a threat to the long-term effectiveness of pneumococcal vaccination. One of the main drivers for serotype replacement is likely to be the competitive interactions between pneumococcal serotypes.
  
  
  METHODS
  We used longitudinal datasets of pneumococcal colonization among infants (American Indian and The Gambia) and toddlers (Denmark) to study the strength and mechanism of competition between pneumococcal serotypes. We characterized the strength of competition as the relative reduction in the expected time spent colonized with two serotypes (double colonization) as compared with colonization with no competition. We also assessed the mechanism of competition, that is, whether reduction in double colonization is due to reduced rate of acquisition or enhanced clearance of colonization. The three datasets were analyzed assuming both perfect (100%) and imperfect (50%) sensitivity in detection of double colonization.
  
  
  RESULTS
  Each dataset showed strong between-serotype competition, and competition in acquisition was clearly identified. These findings remained in the secondary analysis assuming only 50% sensitivity to detect double colonization. Inferences about enhanced clearance due to competition were susceptible to the assumed sensitivity of detection.
  
  
  CONCLUSIONS
  Strong competition between pneumococcal serotypes can explain the prompt replacement by the nonvaccine serotypes in vaccinated persons and populations. The main mechanism of between-serotype interaction was identified as competition in acquisition, which suggests that replacement in pneumococcal disease depends largely on propensities of the replacing serotypes to cause disease through acquisition of colonization.
authors.affiliation: Department of Vaccination and Immune Protection, National Institute for Health and Welfare, Helsinki, Finland. juha.mehtala@thl.fi
authors.forename: Juha
authors.initials: J
authors.lastname: Mehtälä
authors.forename: Martin
authors.initials: M
authors.lastname: Antonio
authors.forename: Margit S
authors.initials: MS
authors.lastname: Kaltoft
authors.forename: Katherine L
authors.initials: KL
authors.lastname: O'Brien
authors.forename: Kari
authors.initials: K
authors.lastname: Auranen
mesh_terms: D002675:Child, Preschool; D015169:Colony Count, Microbial; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D008954:Models, Biological; D011008:Pneumococcal Infections / Q000382:microbiology* / Q000517:prevention & control; D022242:Pneumococcal Vaccines / Q000276:immunology*; D013296:Streptococcus pneumoniae / Q000145:classification* / Q000302:isolation & purification
chemical_list: D022242:Pneumococcal Vaccines