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Abstract

Recently we demonstrated that, after chemotherapy, pediatric patients frequently lose the protective humoral immunity induced by vaccination, with the degree of loss varying according to the type of vaccination (52% for hepatitis B, 25% for measles, 21% for mumps, 18% for rubella, 13% for tetanus, and 8% for polio).1 It is interesting to note that the administration of a booster vaccination to 51 patients enabled all but 3 patients to recover protective antibody titers. In their study, Fioredda et al. did not find a comparable percentage of loss of hepatitis B antibody in a smaller study conducted at two other Italian pediatric centers.2 In view of this, they suggest continuing the vaccination schedule on the basis of the patient's age and do not advocate any booster immunizations. In contrast to our study, the effect of chemotherapy on the loss of protective antibody titers is not clear from these data because of the lack of any assessment of the patient's serologic status before chemotherapy. Differences in patient age at the time of diagnosis, type of malignancy, chemotherapy protocol, and the time to assessment of the antibody levels after the completion of chemotherapy may explain in part the differences between the two studies. Regardless, a major impairment of humoral immunity against hepatitis B has been reported previously in other immunocompromised patients such as those who are positive for the human immunodeficiency virus and patients undergoing hemodialysis.3, 4 Conversely, Laws et al. state that higher losses of protective antibody titers have been observed in children after chemotherapy (20–70% of children for diphtheria and in up to 72% of children for polio). These authors consider that revaccination is the best tool with which to reconstitute protective antibody titers, although their reported response rate was as low as 30% after the first booster and only 60% after a second booster vaccination for diphtheria.5 These data suggest that standard nonmyeloablative chemotherapy can definitely delete specific memory B-cell clones obtained by vaccination and that no spontaneous recovery is expected. This point requires further confirmation but, if true, the lack of epidemiologic data concerning the incidence of vaccine-preventable diseases among children after chemotherapy may reduce the strength of the case for revaccination. In other words, we do not know whether these children are really at risk of developing such diseases or if the immunity of the rest of population will protect them, at least for diseases such as diphtheria and polio.6 The different opinions expressed by several authors clearly reflect the diversity of data regarding vaccine-specific immune recovery after standard chemotherapy. This point is crucial to deciding which strategy of (re-)immunization after chemotherapy (if any) is needed and further prospective studies concerning this important issue are advocated. Simone Cesaro M.D.*, Ruggiero D'Elia M.D. , * Clinic of Pediatric Hematology Oncology, Department of Pediatrics, University of Padova, Padova, Italy, Service of Infectious Disease in, the Pediatric Immunocompromised Host, Department of Pediatrics, University of Padova, Padova, Italy