How Necessary is it to Revaccinate Hemopoietic Transplant Recipients?

Abstract

The loss of specific immunity against vacci nation-preventable diseases after hemopoietic stem cell transplantation (HSCT) was repeatedly reported in the literature during the 1980s and 1990s. Those observations, mainly based on quantitative antibody assays, led to the gener ation of various schemes for the revaccination of HSCT recipients [1,101]. Although based on a low level of evidence and differing in the recommended timing to start the revaccination program, all recommendations followed common patterns (e.g., administering live vaccines only after the first year post-HSCT and delaying immunizations in the event of graft-versus-host disease). Following these revaccination guidelines seems to reassure clinicians and appears to satisfy transplant physicians. Also, from a public health perspective, revaccinating the increasing population of long-term HSCT survivors may reduce the impact that these patients may have in the protection of the overall population. Conversely, reimmunizing HSCT recipients may protect them against the risks derived from the growing tendency to disregard the advice to vaccinate children against certain diseases [2,3]. It would therefore appear that “all is well”, as the scientific community has accepted that the low post-HSCT antibody titers translate into a loss of protection, and the implementation of revaccination schedules appears to correct this deficiency [4,5]. However, from a transplantation immunology point of view, a key question remains unanswered: have the post-HSCT antibody titers for these diseases ever been compared with those of age-paired healthy volunteers? Or, in other words, have we investigated whether it is really necessary to revaccinate these patients in the first place?