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Infection with Haemophilus influenzae type b (Hib) can be life-threatening and is a major cause of meningitis in children. The incidence of H. influenzae infection in children under age five years is estimated to be between 67 and 129 cases per 100,000 children per year. The incidence of Hib infection among children with leukemia is much higher, due to the reduced immune function of these patients. The incidence of Hib disease in this population is about seven times that of the population in general. While it would seem that children with leukemia would be prime candidates for protective immunization, there is also some suggestion that children with leukemia do not respond well to Hib vaccines. In an investigation of the response of children to the newly available, and more efficacious, conjugated Hib vaccines, 50 children with leukemia were immunized; only half developed a satisfactory immune response. When the children who had received leukemic therapy for less than one year were considered separately, the response rate rose to 75 percent. Among those children treated longer, the response rate was only 18 percent. Furthermore, it was found that the use of additional inoculations to boost the response was of little or no value. The authors emphasize that their observations may not be valid for children treated at other institutions using different chemotherapeutic protocols. Nevertheless, it seems reasonable to suggest that children newly diagnosed with leukemia should have immunizations scheduled as rapidly as practical. (Consumer Summary produced by Reliance Medical Information, Inc.)