Inclusion Criteria:  Age 18 or older High performance liquid chromatography (HPLC) confirmed diagnosis of SCD (not applicable to participating donors). An indication for and a planned matched sibling or haploidentical donor non-myeloablative HSCT at the Amsterdam UMC, location AMC (not applicable to patients in cohort 2 (control group) and participating donors) Written informed consent  Exclusion Criteria:  History of either cleared, chronic or active HBV infection (positive HBsAg, anti-HBs, anti-HBc and/or HBV DNA) History of auto-immune diseases and/or use of immunosuppressive drugs History of HIV infection Known hypersensitivity to yeast of any vaccine constituent Donor with a history of HBV infection