EVALUATION OF BOOSTER DOSES, OF HAEMOPHILUS-INFLUENZAE TYPE-B TETANUSTOROID CONJUGATE VACCINE IN 18-MONTH-OLD CHILDREN

A booster dose of Haemophilus influenzae type b conjugate vaccine in t he second year of life is the final step in the recommended series of doses to protect infants from invasive infection. This study assessed the safety and immunogenicity of PRP-T conjugate vaccine booster doses (Act-HIB(R), Connaught Laboratories Ltd), The participants were 367 h ealthy children who had taken part in a study of primary immunization with PRP-T. At 18-19 months old, subjects were randomly assigned to re ceive diphtheria-pertussis-tetanus (DPT) and PRP-T vaccines either mix ed in one syringe (n = 183) or separately in opposite limbs (n = 184). Adverse events were monitored for 48 h after immunization, Blood was obtained prior to vaccination in half of the subjects (combined inject ions group) and following vaccination in all subjects to test for anti bodies to each of the antigens administered. Local adverse reactions w ere infrequent with PRP-T alone and equally frequent at sites of DPT o r DPT/PRP-T injection, except for redness greater than or equal to 25 mm in diameter which was more frequent after the combined vaccines (25 .1 versus 14.1%, p<0.01). Systemic adverse events did not differ in ty pe or frequency betwen groups, Before immunization, the geometric mean anti-PRP level in those tested was 0.41 mu g ml(-1); 26.7% had levels below 0.15 mu g ml(-1). Both treatment groups responded strongly to v accination. In those serially tested anti-PRP levels rose by over 90-f old, to 38.1 mu g ml(-1). No difference existed between postimmunizati on anti-PRP levels in those given PRP-T separately or mixed with DPT. No intergroup differences existed for postimmunization levels of dipht heria, tetanus or pertussis antibodies tested, We conclude that booste r doses of PRP-Tare safe and highly immunogenic even when mixed in one syringe with DPT vaccine.