[COVID-19 vaccination for allogeneic hematopoietic stem cell recipients]

The novel coronavirus disease 2019 (COVID-19) is caused by acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Hematopoietic stem cell transplant (HSCT) recipients are at increased risk of mortality and morbidity with COVID-19 due to severe immune dysfunction. Recombinant adenovirus vector-based vaccine, such as AstraZeneca ChAdOx1, and mRNA-based vaccines, such as Pfizer BNT162b2 and Moderna mRNA-1273 have been used in Japan. COVID-19 vaccine administration to HSCT recipients was reported to result in a 68-96.5% seroconversion for the spike protein. Factors associated with the absence of humoral responses were the time-interval from HSCT to vaccination, absolute lymphocyte count, systemic immunosuppressive treatments, graft versus host disease (GVHD), B-cell count, and hypogammaglobulinemia. New onset and exacerbation of chronic GVHD have been reported as an adverse events associated with vaccination. COVID-19 vaccination of HSCT recipients is relatively safe, and recipients should be vaccinated against COVID-19 6 months after transplantation. In the future, it is necessary to consider passive immunotherapy for HSCT patients who do not benefit from COVID1-19 vaccination.