Jörg Halter

Introduction Patients after allogeneic stem cell transplantation are at high risk for infection‐related complications, and vaccination efficacy might be impaired depending on the immune reconstitution. In this study, we evaluate their response to mRNA vaccines against SARS‐CoV‐2. Methods During routine follow‐up visits, patients were asked about their vaccination status and if they had a previous infection with SARS‐CoV‐2. In fully vaccinated patients, the antibody titer was measured using the Roche Elecsys Anti‐SARS‐CoV‐2 S test. A titer of <1 U/L was considered as negative, titers of ≥250 U/ml as a high antibody titer, and a titer of 50–249 U/ml as a low antibody titer. Patient characteristics were evaluated by chart review to identify risk factors for poor vaccination response. Results The majority of patients developed a high antibody titer (138 out 182 patients, 75.8%). Risk factors for a low antibody titer were immunosuppressive therapy, a lymphocyte count <0.9 G/L, ongoing treatment for the underlying malignancy, and active graft‐versus‐host disease (GvHD). Donor type, underlying disease, a previous SARS‐CoV‐2 infection, and sex did not significantly influence the response to the vaccination. Discussion While patients undergoing allogeneic stem cell transplantation have been excluded from the initial registration trials, our real‐world experience with a large patient cohort confirms the data of previous studies, showing that most patients do have a good response to mRNA vaccines against SARS‐CoV‐2. Nevertheless, a significant proportion of patients shows an inadequate vaccination, which can be improved after a third vaccination in most cases despite immunosuppressive therapy. image