title: Immunologic considerations for the timing of the booster dose of 7-valent pneumococcal conjugate vaccine in young children.
abstract: BACKGROUND
  The booster (fourth) dose of 7-valent pneumococcal conjugate vaccine (PCV7) is recommended to be given at 12-15 months but in Canada it better fits the national schedule at 18 months, prompting this comparison of the safety and immunogenicity of booster immunization at 15 or 18 months.
  
  
  METHODS
  Children who had completed a study of primary PCV7 immunization (with final serology at 7-8 months of age) were enrolled at 12 months, bled and randomly assigned to receive a PCV7 booster at age 15 or 18 months, with serologic testing before and 4 weeks afterward. Adverse events were documented for 3 days postbooster. Antibody concentrations were measured for the 7 pneumococcal serotypes and Haemophilus influenzae type b at 7-8, 12, 15 or 18 months and after boosting.
  
  
  RESULTS
  Three hundred thirty-one children were boosted, 167 at 15 months and 164 at 18 months. Pneumococcal geometric mean antibody concentrations declined by 15 months to 23.4% of peak geometric mean concentrations at age 7-8 months and to 19.8% by 18 months. Spontaneous increases in 1 or more antibody concentrations were noted in 195 subjects (61.7%), most commonly with types 6B and 19F. Antibody responses to PCV7 were similarly brisk at 15 and 18 months. Mild injection-site redness and swelling were significantly more frequent at 15 than 18 months but no other differences in reactogenicity were observed.
  
  
  CONCLUSIONS
  Residual antibody concentrations differed minimally between 15 and 18 months. Spontaneous antibody increases often occurred before boosting, possibly from colonization. PCV7 booster vaccination at 18 months appears to be safe and provides comparable immunogenicity to 15 months vaccination.
authors.affiliation: Vaccine Evaluation Center, BC Children's Hospital and the University of British Columbia, Vancouver, BC, Canada. dscheifele@cw.bc.ca
authors.forename: David W
authors.initials: DW
authors.lastname: Scheifele
authors.forename: Scott A
authors.initials: SA
authors.lastname: Halperin
authors.forename: Jan J
authors.initials: JJ
authors.lastname: Ochnio
authors.forename: Michelle
authors.initials: M
authors.lastname: Mozel
authors.forename: Denzyl
authors.initials: D
authors.lastname: Duarte-Monteiro
authors.forename: David
authors.initials: D
authors.lastname: Wortzman
mesh_terms: D000907:Antibodies, Bacterial / Q000097:blood; D005260:Female; D006801:Humans; D007117:Immunization, Secondary; D007223:Infant; D008297:Male; D022401:Meningococcal Vaccines / Q000008:administration & dosage / Q000009:adverse effects / Q000276:immunology*; D013997:Time Factors
chemical_list: D000907:Antibodies, Bacterial; D022401:Meningococcal Vaccines