RESPONSE TO A BOOSTER DOSE OF H.influenzae TYPE B CAPSULAR POLYSACCHARIDE - DIPHTERIA TOXOID CONJUGATE VACCINE (PRP-D) IN CHILDREN INITIALLY IMMUNIZED AT 3- 5-7 OR ONLY 7 MONTHS

摘要

22 three months old children received three doses of PRP-D at 2 months intervals, and 21 only one dose when 7 months old. In both groups half of the children received booster immunization at 14 months, and the other half at 18 months. Sera were obtained prior and post immunizations and anti-PRP antibody levels were measured by Farr-type RIA. The vaccine was well tolerated; only mild reactions were noted. The antibody responses to initial immunization have already been published (Lancet, 1985): The third dose at 7 months resulted in high antibody levels, whereas only one dose at 7 months did not. The geometric mean (GM) antibody levels before booster immunization at 14 months were 1.02 ug/ml in children who had received 3 doses of PRP-D and 0.22 ug/ml when only 1 dose had been given.The post booster levels (GM) were 40.41, 43.56, 25.41 and 37.21 ug/ml in the four groups. All groups differed significantly from any group of children of the same age immunized with PRP only (GM levels below 1 ug/ml).In conclusion. A PRP-D booster given at 14 or 18 months to children who were previously immunized at 3-5-7 or only 7 months was well tolerated and resulted in significantly higher antibody levels than immunization by PRP alone does. This suggests that PRP-D can induce a real booster effect.