title: Haemophilus influenzae type b conjugate vaccine diluted tenfold in diphtheria-tetanus-whole cell pertussis vaccine: a randomized trial.
abstract: BACKGROUND
  Despite their proven efficacy Haemophilus influenzae type b (Hib) conjugate vaccines are not given to most children in the developing world in the face of an estimated global Hib disease burden of nearly 2 million cases per annum. A major barrier to the introduction of the vaccine would be overcome by diluting the vaccine 10-fold in diphtheria-tetanus-whole cell pertussis (DTP). We report a randomized trial comparing the use of Hib conjugate vaccine diluted in a multidose vial of DTP with that of the full Hib dose.
  
  
  METHODS
  We randomized 168 infants to receive either the full dose Hib polysaccharide-tetanus toxoid conjugate (PRP-T) vaccine or a 1/10 dilution prepared by reconstituting the full dose in a 10-dose DTP vial. Infants were vaccinated at 6, 10 and 14 weeks of age and received a full dose as a test of immunologic memory at 9 months of age. Sera were collected at each visit and at 1 week after the booster dose. Serum anti-capsular PRP antibody concentrations were measured by enzyme-linked immunosorbent assay.
  
  
  RESULTS
  After the primary vaccination series, 95% of infants in the full dose arm and 94% of infants in the 1/10 dose arm achieved anti-PRP IgG antibody concentrations of > or = 1.0 microg/ml. Infants receiving the diluted vaccine had significantly higher titers of anti-PRP antibody in response to the booster dose (151.36 microg/ml vs. 68.55 microg/ml, P = 0.009).
  
  
  CONCLUSIONS
  The 1/10 dose of PRP-T was as immunogenic and safe as the full dose. The technique of diluting a single dose of PRP-T in a 10-dose DTP vial could potentially allow the widespread introduction of Hib vaccine in resource-poor countries currently unable to afford full dose Hib conjugate vaccine.
authors.affiliation: Pneumococcal Diseases Research Unit of the Medical Research Council, South African Institute for Medical Research and University of the Witwatersrand, Johannesburg, South Africa.
authors.forename: Mark
authors.initials: M
authors.lastname: Nicol
authors.forename: Robin
authors.initials: R
authors.lastname: Huebner
authors.forename: Rosalia
authors.initials: R
authors.lastname: Mothupi
authors.forename: Helena
authors.initials: H
authors.lastname: Käyhty
authors.forename: Nontombi
authors.initials: N
authors.lastname: Mbelle
authors.forename: Esther
authors.initials: E
authors.lastname: Khomo
authors.forename: Keith P
authors.initials: KP
authors.lastname: Klugman
mesh_terms: D000914:Antibodies, Viral / Q000032:analysis; D000917:Antibody Formation; D016667:Bacterial Capsules; D003906:Developing Countries; D015721:Diphtheria-Tetanus-Pertussis Vaccine / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D005260:Female; D018073:Haemophilus Vaccines / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology; D006801:Humans; D007223:Infant; D008297:Male; D011135:Polysaccharides, Bacterial / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology
chemical_list: D000914:Antibodies, Viral; D015721:Diphtheria-Tetanus-Pertussis Vaccine; D018073:Haemophilus Vaccines; C044237:Haemophilus influenzae type b polysaccharide vaccine; D011135:Polysaccharides, Bacterial