title: Are anticapsular antibodies the primary mechanism of protection against invasive pneumococcal disease?
abstract: BACKGROUND
  Antibody to capsular polysaccharide has been the basis of several vaccines that offer protection against invasive disease from Streptococcus pneumoniae. The success of such vaccines has led to the inference that natural protection against invasive pneumococcal disease is largely conferred by anticapsular antibody. If this is so, one would expect that the decline in disease from different serotypes would vary significantly, and that the appearance of substantial concentrations of anticapsular antibodies would coincide temporally with the decline in age-specific incidence.
  
  
  RESULTS
  Using incidence data from the United States, we show that, on the contrary, the decline in incidence with age is quite similar for the seven most important serogroups, despite large differences in exposure in the population. Moreover, only modest increases in antibody concentration occur over the second and third years of life, a period in which serotype-specific incidence declines to less than 25% of its peak. We also present detailed data on the distribution of antibody concentrations in Israeli toddlers, which are consistent with the United States findings. The same conclusion is supported by new data on age-specific incidence in Finland, which is compared with published data on antibody acquisition in Finnish toddlers.
  
  
  CONCLUSIONS
  We suggest some additional studies of the mechanisms of protection that could distinguish among potential alternative mechanisms, including acquired immunity to noncapsular antigens, maturation of nonspecific immune responses, or changes in anatomy or exposure.
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA. mlipsitc@hsph.harvard.edu
authors.forename: Marc
authors.initials: M
authors.lastname: Lipsitch
authors.forename: Cynthia G
authors.initials: CG
authors.lastname: Whitney
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Zell
authors.forename: Tarja
authors.initials: T
authors.lastname: Kaijalainen
authors.forename: Ron
authors.initials: R
authors.lastname: Dagan
authors.forename: Richard
authors.initials: R
authors.lastname: Malley
mesh_terms: D000367:Age Factors; D000907:Antibodies, Bacterial / Q000276:immunology / Q000627:therapeutic use*; D000917:Antibody Formation; D002675:Child, Preschool; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007223:Infant; D011008:Pneumococcal Infections / Q000276:immunology* / Q000517:prevention & control*; D022242:Pneumococcal Vaccines / Q000276:immunology*; D011135:Polysaccharides, Bacterial / Q000276:immunology*
chemical_list: D000907:Antibodies, Bacterial; D022242:Pneumococcal Vaccines; D011135:Polysaccharides, Bacterial