title: Persistence of IgG antibody following routine infant immunization with the 7-valent pneumococcal conjugate vaccine.
abstract: BACKGROUND
  Pneumococcal conjugate vaccine (PCV) induces protective anticapsular IgG, which mediates disease immunity. IgG persistence may influence long-term protection.
  
  
  METHODS
  An observational, prospective, longitudinal study of nasopharyngeal carriage among American Indian households from 2006 to 2008 evaluated long-term immunogenicity of 7-valent PCV (PCV7). Children unimmunized with PCV were age-matched to those PCV7 immunized at least 4 years prior (ratio 1:3 or 1:4). Blood collected at the final study visit was analyzed for PCV7 serotype IgG (enzyme-linked immunosorbent assay) and for functional activity (multiplex-opsonophagocytic assay) for serotypes 4, 6B, 14 and 23F. Geometric mean concentrations (GMCs), titers (GMTs) and the odds of serotype-specific IgG ≥0.35 μg/mL were compared according to immunization status using a matched regression approach.
  
  
  RESULTS
  Eight unimmunized and 28 immunized children age-matched at the time of serum collection (mean age: 7.9 years) were included. Serotype-specific GMCs, GMTs and proportions above the correlate of protection did not differ between the groups except for serotypes 14 and 23F. Serotype 14 GMCs (immunized 0.7 vs. unimmunized 0.2; P = 0.02) and serotype 23F GMTs (immunized 388.3 vs. unimmunized 47.8; P = 0.03) were significantly higher among immunized children. IgG concentrations and functional titers among immunized children were strongly correlated for serotypes 4 (r = 0.78; P ≤ 0.001) and 14 (r = 0.52; P ≤ 0.01).
  
  
  CONCLUSIONS
  PCV serotype-specific IgG concentrations 4 years following PCV vaccination do not persist above natural levels for most serotypes. Exposure to pneumococcus may be critical in maintaining persistent serotype-specific IgG; the elimination of circulating vaccine type pneumococci by PCV may have effects on long-term immunity.
authors.affiliation: From the *Department of International Health, Center for American Indian Health, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland; and †Institute Child Health, University College London, London, United Kingdom.
authors.forename: Lindsay R
authors.initials: LR
authors.lastname: Grant
authors.forename: Polly
authors.initials: P
authors.lastname: Burbidge
authors.forename: Mitch
authors.initials: M
authors.lastname: Haston
authors.forename: Marina
authors.initials: M
authors.lastname: Johnson
authors.forename: Raymond
authors.initials: R
authors.lastname: Reid
authors.forename: Mathuram
authors.initials: M
authors.lastname: Santosham
authors.forename: David
authors.initials: D
authors.lastname: Goldblatt
authors.forename: Katherine L
authors.initials: KL
authors.lastname: O'Brien
mesh_terms: D000907:Antibodies, Bacterial / Q000097:blood*; D002648:Child; D005260:Female; D000069443:Heptavalent Pneumococcal Conjugate Vaccine / Q000008:administration & dosage* / Q000276:immunology*; D006801:Humans; D007114:Immunization / Q000706:statistics & numerical data*; D007074:Immunoglobulin G / Q000097:blood*; D007198:Indians, North American / Q000706:statistics & numerical data; D008137:Longitudinal Studies; D008297:Male; D011008:Pneumococcal Infections / Q000517:prevention & control; D011446:Prospective Studies; D013296:Streptococcus pneumoniae / Q000276:immunology
chemical_list: D000907:Antibodies, Bacterial; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D007074:Immunoglobulin G