Safety and immunogenicity of BNT162b2 mRNA COVID-19 vaccine in Japanese patients after allogeneic stem cell transplantation

Patients who have undergone hematopoietic stem cell transplantation (HSCT) for hematological disease experience high mortality when infected by coronavirus disease 2019 (COVID-19). However, the safety and efficacy of COVID-19 vaccine in HSCT patients remains to be investigated. We prospectively evaluated the safety and immunogenicity of BNT162b2 mRNA COVID-19 vaccine (Pfizer BioNTech) in 25 Japanese allogeneic HSCT patients in comparison with 19 healthy volunteers. While anti-S1 antibody titers in almost all healthy volunteers after the second dose were higher than the cut-off value reported previously, levels in HSCT patients after the second dose were diverse. Nineteen patients (76%) got seroconversion of anti-S1 IgG. Median optical density of antibody levels in HSCT patients with low IgG levels (< 600 mg/dL), steroid treatment, or low lymphocytes (< 1000 /μL) was significantly lower than that in the other HSCT patients. There were no serious adverse events (> Grade 3), no new development or exacerbation of graft-versus-host disease after vaccination. We concluded BNT162b2 mRNA vaccine is safe and effective in Japanese allogeneic HSCT patients.