HAEMOPHILUS-INFLUENZAE TYPE-B POLYSACCHARIDE-TETANUS PROTEIN CONJUGATE VACCINE DOES NOT DEPRESS SEROLOGIC RESPONSES TO DIPHTHERIA, TETANUS OR PERTUSSIS ANTIGENS WHEN COADMINISTERED IN THE SAME SYRINGE WITH DIPHTHERIA-TETANUS-PERTUSSIS VACCINE AT 2, 4 AND 6 MONTHS OF AGE

The safety and immunogenicity of a vaccine against Haemophilus influen zae type b consisting of purified polyribosylribitol phosphate conjuga ted to tetanus toxoid (PRP-T) were evaluated in 277 Chilean infants wh o were randomly assigned to one of three treatment groups: Group A, PR P-T mixed with diphtheria-tetanus-pertussis (DTP) vaccine in a single syringe and given as a single inoculation in one arm and placebo in th e other arm; Group B, PRP-T given in one arm and DTP in the other arm; Group C, DTP given in one arm and placebo in the other. Infants were immunized at 2, 4 and 6 months of age and examined daily for 4 days af ter each immunization. Serum PRP antibodies; tetanus, diphtheria and p ertussis antitoxin; pertussis agglutinins; and antibodies to Bordetell a pertussis filamentous hemagglutinin were measured at baseline and 2 months after each dose. PRP-T was well-tolerated. After three doses of PRP-T vaccine 100% of infants attained PRP antibody concentrations gr eater-than-or-equal-to 0.15 mug/ml and 96 to 99% achieved high anti-PR P concentrations (greater-than-or-equal-to 1.0 mug/ml). The post-third dose anti-PRP geometric mean titer was high (6.94 mug/ml) in infants who were given PRP-T combined with DTP, although it was somewhat lower than the geometric mean titer of the group who received PRP-T in a se parate arm (9.93 mug/ml) (P not significant). No differences were dete cted among the groups in tetanus antitoxin response, whereas after two or three doses the geometric mean titer of diphtheria antitoxin was s ignificantly higher in the group who received PRP-T combined with DTP than in the group who received PRPT as a separate inoculation (P < 0.0 16). Pertussis agglutinin, antitoxin and anti-filamentous hemagglutini n responses did not differ among the groups. These results encourage c oadministration of PRP-T and DTP in a single inoculation, in view of t he practical advantages of such combined immunization.