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February 5, 1992

Impact of Haemophilus influenzae Type b Polysaccharide-Tetanus Protein Conjugate Vaccine on Responses to Concurrently Administered Diphtheria-Tetanus-Pertussis Vaccine

Author Affiliations

From the Center for Vaccine Development, University of Maryland School of Medicine, Baltimore (Drs Clemens, Ferreccio, and Levine, and Mr Rao); Division of Epidemiology, Statistics, and Prevention Research, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Md (Dr Clemens and Mr Rao); Ministry of Health, Republic of Chile (Dr Ferreccio); Department of Pediatrics, Roberto del Rio Hospital, Santiago (Dr Horwitz); Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, Tenn (Dr Edwards); and Pasteur Mérieux Sérums et Vaccins, Marcy l'Etoile, France (Dr Fritzell).

JAMA. 1992;267(5):673-678. doi:10.1001/jama.1992.03480050077028

Objective.  —To assess whether serum antibody responses to diphtheriatetanus-pertussis (DTP) vaccine were affected by coadministration of Haemophilus influenzae type b capsular polyribosylribitol phosphate polysaccharide-tetanus protein (PRP-T) conjugate vaccine when given to patients at 2, 4, and 6 months of age.

Design.  —Randomized, double-blind clinical trial.

Setting.  —Urban Santiago, Chile.

Patients.  —Healthy infants assembled from health centers. Two hundred seventy-eight (74%) of 375 eligible infants participated; 222, who complied with the complete protocol, constituted the primary group under analysis.

Interventions.  —One of three vaccine regimens was given to study participants at 2,4, and 6 months of age, either DTP mixed in the same syringe as PRP-T (group 1); DTP and PRP-T given at separate injection sites (group 2); or DTP without PRP-T (group 3).

Primary Outcome Measures.  —Titers of serum antidiphtheria toxoid, antitetanus toxoid, and pertussis agglutinin antibodies were measured in blood samples taken from patients 2 months after each dose.

Results.  —Serum antidiphtheria toxoid and antitetanus toxoid responses showed no important depressions in the patients receiving PRP-T. In contrast, geometric mean titers (GMTs) of pertussis agglutinins, expressed as reciprocal serum dilutions, after both the second and third doses (GMT2, GMT3) were lowest in group 1 (GMT2 = 89; GMT3 = 1230), intermediate in group 2 (GMT2 = 123; GMT3 = 1995), and highest in group 3 (GMT2 = 210; GMT3=3090; P<.05 for trend group 1<group 2<group 3 after each dose). Antipertussis toxin and antipertussis filamentous hemagglutinin antibody titers also were depressed in patients who received PRP-T. Follow-up of a subset at 18 months revealed an expected decline of pertussis agglutinin titers to near baseline levels in each group.

Conclusions.  —Concurrent administration of PRP-T vaccine with DTP vaccine, either in the same syringe or at different sites, interfered with antipertussis responses to a primary series of immunizations. Although the clinical significance of this antagonism is uncertain, these data underscore the caution required in decisions to add new vaccines to existing immunization regimens.(JAMA. 1992;267:673-678)