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)