Risk of Haemophilus influenzae type b disease in children with cancer and response of immunocompromised leukemic children to a conjugate vaccine.

From 1969 to 1988, 8 cases of systemic Haemophilus influenzae type b (Hib) disease occurred among 5288 patients with cancer. For the first 4 years of life, systemic Hib disease was significantly greater in leukemic children than in the general population (606/100,000 vs. 90/100,000, respectively). Fifty children aged 2-6 years with acute leukemia were vaccinated with a Hib conjugate vaccine, ProHibit. The overall response rate was 50%; however, 75% of children receiving leukemic therapy for less than 12 months responded versus 18% of those treated longer. After vaccination, the geometric mean antibody concentration was 7.2 micrograms/ml, appreciably lower than for normal children of similar ages. After 12 months, the geometric mean antibody concentration had declined to 0.35 micrograms/ml, and 75% of subjects had antibody levels greater than or equal to 0.15 micrograms/ml. A booster dose for unsuccessfully vaccinated subjects was of minimal benefit. Children with acute leukemia in remission who were treated according to the leukemia therapy protocol of St. Jude Children's Research Hospital had a good likelihood of responding to the conjugate Hib vaccine if administered within a year of initiation of chemotherapy.