Immunogenicity and safety of the BNT162b2 mRNA COVID-19 vaccine in haematopoietic stem cell transplantation recipients

The immunogenicity and safety of Pfizer-BioNTech BNT162b2 mRNA vaccine in allogeneic haematopoietic stem cell transplantation (HSCT) recipients are unknown. We prospectively followed 152 HSCT recipients who were at least six months following transplantation and with no active acute graft-versus-host disease (GVHD). Blood samples were taken 2-4 weeks after the second vaccination and analyzed for receptor-binding domain (RBD) antibodies and neutralizing antibodies (NA). 272 immunocompetent healthcare workers served as controls. At a median of 28 days after the second vaccination, 118 patients (77 center dot 6%) developed RBD immunoglobulin G (IgG) with a geometric mean titre (GMT) of 2 center dot 61 [95% CI (confidence interval), 2 center dot 16-3 center dot 16]. In the control group 269/272 (98 center dot 9%) developed RBD IgG, with a GMT of 5 center dot 98 (95% CI 5 center dot 70-6 center dot 28), P < 0 center dot 0001. The GMT of NA in HSCT recipients and controls was 116 center dot 0 (95% CI 76 center dot 5-175 center dot 9), and 427 center dot 9 (95% CI 354 center dot 3-516 center dot 7) respectively (P < 0001). Multivariate logistic regression analysis revealed that HSCT recipients with no chronic GVHD and no immunosuppressive therapy at the time of vaccination had significantly higher levels of NA following the second vaccination. Adverse events were minimal and were less common than in healthy controls. In conclusion; the BNT162b2 mRNA vaccination is safe and effective in HSCT recipients, especially those who are immunosuppression-free. A significant fraction developed protecting NA.