ABSTRACT
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 the response of 182 patients to mRNA vaccines against SARS-CoV2. Methods: During routine follow up visits, patients were asked about their vaccination status and if they had a previous infection with SARS-CoV2. In fully vaccinated patients, the antibody titer was measured using the Roche Elecsys Anti-SARS-CoV2 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 im-munosuppressive therapy, a lymphocyte count <0.9 G/l, ongoing treatment for the underlying malignancy and active GvHD. The vaccine (Moderna vs Pfizer), donor type, underlying disease, a previous SARS-CoV2 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 large patient cohort confirms the data of previous smaller studies, showing that most patients do have a good response to mRNA vaccines against SARS-CoV2. Nevertheless, a significant proportion of patients shows an inadequate vaccination response and thus qualifies for a third vaccination.