IMMUNOGENICITY AND SAFETY OF HAEMOPHILUS-INFLUENZAE TYPE-B CAPSULAR POLYSACCHARIDE TETANUS CONJUGATE VACCINE (PRP-T) PRESENTED IN A DUAL-CHAMBER SYRINGE WITH DTP

Separate injections of Haemophilus influenzae type b capsular polysacc haride-tetanus conjugate (PRP-T) vaccine and diphtheria-tetanus-pertus sis (DTP) reconstitution of freeze-dried PRP-T vaccine with liquid DTP vaccine have been shown to be safe and immunogenic in infants. The pr esent study was conducted to test the safety and immunogenicity of the liquid combination vaccine administered to young infants in the dual- chamber syringe. The study was a monocenter. open clinical trial of 3 month-old infants receiving PRP-T and DTP vaccines in the dual-chamber syringe reconstituted prior to injection. Healthy infants were immuni zed according to a 3, 4 and 5 months-of-age schedule. The vaccine was administered in a dual-chamber syringe, ready to use with two chambers . The proximal chamber contained freeze-dried PRP-T and the distal cha mber contained liquid combination-vaccine DTP. The freeze-dried PRP-T vaccine was reconstituted with the liquid DTP vaccine in the same unid ose dual-chamber syringe (0.5 mL) and was injected intramuscularly int o the deltoid region. Blood sampling was performed prior to vaccinatio n at 3 months of age and after the third vaccination at 6 months. The primary end-point was the serological response to PRP-T vaccine as exp ressed by the percentage of infants with an antibody titer greater tha n or equal to 1 mu g/mL. The reactogenicity was expressed as the perce ntage of reported local and systemic reactions. A total of 108 infants were included in the study and received the dual-chamber syringe vacc ine. After the third injection, all the infants had a PRP antibody tit er greater than or equal to 0.15 mu g/mL and 94.4% of infants had a PR P antibody titer greater than or equal to 1 mu g/mL; the pertussis agg lutinin titers were over the threshold 40 and 80 in all infants and 98 .1% were over the threshold 320. After the third injection, all the in fants had diphtheria. antibody titers greater than 0.1 IU/mL and 83.3% had titers greater than 1 IU/mL: all the infants had tetanus antibody titers greater than 0.1 IU/mL and 97.2% had results over 1 IU/mL. Thi rty-seven infants (34.6%) had local reactions and 64.5% had systemic r eactions. The dual-chamber syringe may reduce the cost of vaccine deli very, as well as the workload, and increase the vaccine acceptability and coverage rate of vaccines.