Abstract This was a monocentric prospective study testing the efficacy and safety of a first injection of BNT162b2 (Pfizer‐BioNTech) in 112 Allo‐HSCT patients. Antibody response to SARS‐CoV‐2 spike protein receptor‐binding domain was tested at the time of the second injection (Roche Elecsys). The study also included a non‐randomized control arm of 26 healthy controls. This study shows that a first dose of SARS‐CoV‐2 messenger RNA vaccine is safe and provides a 55% rate of seroconversion in allotransplanted patients compared to 100% for the controls (p < 0.001). Factors influencing the absence of response in patients were recent transplantation (<2 years), lymphopenia (<1 × 109/L) and immunosuppressive treatment or chemotherapy at the time of vaccination.
