Letermovir for Prevention of Cytomegalovirus Reactivation in Haploidentical and Mismatched Adult Donor Allogeneic Hematopoietic Cell Transplantation with Post-Transplantation Cyclophosphamide for Graft-versus-Host Disease Prophylaxis

•Letermovir is effective in reducing clinically significant cytomegalovirus (CMV) infection in haploidentical or mismatched adult unrelated donor allogeneic hematopoietic cell transplantation using post-transplantation cyclophosphamide-based graft-versus host-disease prophylaxis (letermovir, 21.9% versus no letermovir, 68.8%; P< .001).•Persistent CMV infection necessitating >28 days of therapy was more common in patients who did not receive letermovir (31.2% versus 6.2%; P = .02).•Late clinically significant CMV infection is rare if letermovir prophylaxis is continued beyond 14 weeks (1 of 24 patients; 4.2%).