Children receiving chemotherapy for treatment of malignancies are in an immune-compromised state. Immunosuppression occurs due to the underlying malignancy, the cytotoxic therapy the child is receiving, or a combination of these factors. Not only is the child at an increased risk for opportunistic infections, but any immunity associated with vaccines administered prior to chemotherapy is compromised. The loss of vaccine-associated antibody protection occurs in children with leukemia and lymphoma, as well as solid tumors, although the therapy for the former is more lymphotoxic.

Response to newly administered vaccines is also compromised in children undergoing chemotherapy. Immune reconstitution usually occurs 3 to 12 months after the cessation of chemotherapy, but younger children often take longer to recover their immune function. For these reasons, the immunization schedule for a child receiving chemotherapy needs to be altered.

Children receiving chemotherapy should not receive live vaccines because of the risk of developing an active infection from the immunization. Immunization with killed vaccines may be performed in these children. However, the degree of antibody response to vaccines administered while receiving chemotherapy has not been clearly delineated. It seems that immune response is best when vaccines are administered between cycles of chemotherapy. Table 171.1, reviews the recommendations for administration of specific vaccines.

As mentioned earlier, reconstitution of the immune system occurs at variable times in children who have been treated with chemotherapy. The timing and degree of immune reconstitution depends on a variety of factors,

including the type of malignancy, the age of the child, and the intensity of chemotherapy. Antibody titers can be obtained prior to vaccination to determine which series of vaccines are needed. Children should receive boosters following the completion of chemotherapy. As a general rule, immunization with killed vaccines can be resumed 6 months after the completion of chemotherapy, and live vaccines may be administered 12 months after the completion of chemotherapy.