A third dose of mRNA-1273 vaccine improves SARS-CoV-2 immunity in HCT recipients with low antibody response after 2 doses.

Patients with hematologic malignancies treated with autologous (auto) and allogeneic (allo) hematopoietic cell transplantation (HCT) are at high risk of developing adverse outcomes related to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection due to immune dysregulation, prolonged immunosuppression, graft-versus-host disease (GVHD), and cytopenias.1 The estimated incidence of SARS-CoV-2 infection in auto- and allo-HCT is 5.5% and 11%, respectively, with a mortality rate of approximately 20% in the allo-HCT compared with the 1.8% observed in the general United States population.1,2 Vaccination remains the most effective tool in preventing severe COVID-19 disease, hospitalization, and death, and immunization with messenger RNA (mRNA) SARS-CoV-2 vaccines has been highly recommended and prioritized in fragile patients, including HCT.3,4 SARS-CoV-2 mRNA vaccination has shown to overall induce high levels of antibodies in the majority of HCT after 2 vaccine doses, but some patients do not mount an appreciable immune response to SARS-CoV-2 vaccination (Pettini et al; manuscript in preparation).5 Therefore, a third vaccine dose capable of effectively boosting the immune system is particularly critical for low responders who could have a weakened and/or slowed immune priming.(6)