Efficacy and safety of mRNA1273 SARS-CoV-2 vaccination in hematopoietic stem cell transplant recipients: Single center experience

Background: COVID-19 represents a worldwide pandemic and vaccination remains the most effective preventive strategy. Among hematological patients, COVID-19 has been associated with a high mortality rate. Vaccination against SARS-CoV-2 has shown high efficacy in reducing community transmission, hospitalization and deaths related to severe COVID-19 disease. However, patients with impaired immunity may have lower sero-responsiveness to vaccination. Methods: This study focuses on hematopoietic stem cell transplantation (HSCT) recipients. We performed a unicenter, prospective, observational study of a cohort of 31 allogeneic and 56 autologous-HSCT recipients monitored between March 2021 and May 2021 for serological response after COVID-19 vaccination with two doses of mRNA1273 vaccine (Moderna). In order to determine seroconversion, serological status before vaccination was studied. Results: At a median range of 75 days after the second vaccine dose, seroconversion rates were 84% and 85% for the autologous and allogeneic-HSCT groups, respectively. We confirmed some potential risk factors for a negative serological response, such as receiving anti-CD20 therapy in the previous year before vaccination, a low B-lymphocyte count and hypogammaglobulinemia. Neutralizing antibodies were quantified in 44 patients, with a good correlation with serological tests. Adverse events were minimal. Conclusion: mRNA1273 vaccination is safe and effective in HSCT recipients, especially in those presenting recovered immunity.