Humoral response and safety of the BNT162b2 and mRNA-1273 COVID-19 vaccines in allogeneic hematopoietic stem cell transplant recipients: an observational study

Abstract: The effectiveness of mRNA COVID-19 vaccines and the optimal timing of vaccine administration in allogeneic hematopoietic stem cell transplantation (Allo-HSCT) recipients remains inadequately investigated. We examine the effectiveness and safety of mRNA COVID-19 vaccines in allo-HSCT recipients. This prospective observational study included 44 allo-HSCT recipients and 38 healthy volunteers. The proportion of subjects acquiring anti-S1 IgG antibodies were considered as the primary endpoint. The occurrence of adverse events after vaccination and objective deterioration of chronic graft-versus-host disease (GVHD) were defined as secondary endpoints. In addition, we compared anti-S1 antibody titers in subgroups based on time interval between transplantation and vaccination. A humoral response to the vaccine was evident in 40 (91%) patients and all 38 healthy controls. The median anti-S1 IgG titers were 395 and 499 BAU/mL in patients and healthy controls, respectively (p = 0.606). A short time interval between transplantation and vaccination (≤ 6 months) was associated with low anti-S1 IgG antibody titers. No serious adverse events and deterioration of chronic GVHD were observed. Only one case of new development of mild chronic GVHD was recorded. Messenger RNA COVID-19 vaccines induce humoral responses in allo-HSCT recipients and can be administered safely.