title: Nasopharyngeal colonization: a target for pneumococcal vaccination.
abstract: The pneumococcal conjugate vaccine (PCV), licensed in 2000, is highly efficient in preventing serious disease caused by serotypes in the vaccine and also prevents symptomless colonization of the nasopharynx. Prevention of this first step in the infection cycle has important consequences: it reduces chances of spread of the infection and indirectly protects from disease. Through these indirect effects, the protection afforded by the vaccine extends to the whole population, including those not vaccinated (herd immunity). Already now, after 5 years of wide use of PCV for infant immunization in the USA, more cases are prevented through the indirect effects than by vaccine-induced immunity in those vaccinated. The extended protection increases the cost-effectiveness of PCV and should clearly encourage its use in poorly resourced countries. However, the accumulated experience also shows that the herd immunity, due to PCV, is partly offset by replacement of the vaccine serotypes by other, nonvaccine serotypes. Owing to the general reduced virulence of the latter, this has only had a modest effect on disease, but the possibility of more virulent nonvaccine serotypes arising cannot be ignored and should be the focus of continued surveillance.
authors.affiliation: National Public Health Institute, Department of Vaccines, Helsinki, Finland. helena.kayhty@ktl.fi
authors.forename: Helena
authors.initials: H
authors.lastname: Käyhty
authors.forename: Kari
authors.initials: K
authors.lastname: Auranen
authors.forename: Hanna
authors.initials: H
authors.lastname: Nohynek
authors.forename: Ron
authors.initials: R
authors.lastname: Dagan
authors.forename: Helena
authors.initials: H
authors.lastname: Mäkelä
mesh_terms: D000818:Animals; D002353:Carrier State; D002648:Child; D002675:Child, Preschool; D002986:Clinical Trials as Topic; D024881:Drug Resistance, Bacterial; D005060:Europe / Q000453:epidemiology; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D006801:Humans; D032521:Immunity, Herd; D017589:Immunization Programs / Q000639:trends; D007223:Infant; D007231:Infant, Newborn; D022401:Meningococcal Vaccines / Q000276:immunology; D009305:Nasopharynx / Q000382:microbiology*; D011008:Pneumococcal Infections / Q000453:epidemiology / Q000276:immunology / Q000517:prevention & control* / Q000635:transmission; D022242:Pneumococcal Vaccines / Q000276:immunology*; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification / Q000254:growth & development* / Q000276:immunology
chemical_list: C414006:23-valent pneumococcal capsular polysaccharide vaccine; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D022401:Meningococcal Vaccines; D022242:Pneumococcal Vaccines