Cytomegalovirus (CMV), the beta-human herpesvirus type 5 (HHV-5), is a major cause of morbidity in immunocompromised hosts, especially recipients of allogeneic hematopoietic cell transplantation (HCT) or solid organ transplantation. The standard-of-care approach to CMV prevention based on CMV surveillance-guided preemptive therapy is being challenged by the recent approval of letermovir (LMV) for primary prophylaxis. Real-word clinical data show dramatic improvement in the reduction of risk of CMV infection and any CMV viremia in all studies performed so far. LMV is the drug that is breaking the paradigm of preemptive therapy with shift to prophylaxis. A summary of reported data presented in 2019 annual meetings of American Society of Transplantation and Cellular Therapy (ASTCT), European Society for Blood and Marrow Transplantation (EBMT) and American Society of Hematology (ASH), as well as already published results, is presented in this review. A total number of 401 adult high-risk patients on primary prophylaxis after HCT were reported in 11 studies up to January 1, 2020. It was shown that fewer patients in the LMV arms had any CMV reactivation or need for CMV treatment compared with the any other prophylactic or preemptive approaches. In conclusion, LMV is much highly effective than CMV-guided preemptive therapy in preventing CMV infection and CMV disease. The use of LMV in prophylaxis results in an improvement in overall survival during the first 24 and 48 weeks. LMV has a favorable safety profile, as it does not cause myelotoxicity. Current guidelines of European Conference on Infections in Leukemia (ECIL7) recommend LMV for the use in prophylaxis of CMV infection in patients after allogeneic hematopoietic cell transplant.