Real data confirm an excellent toxicity profile and effectiveness of letermovir prophylaxis with decreased cytomegalovirus reactivation and resistance in umbilical cord blood transplantation for both paediatric and adult patients.Commentary on: Yan et al. Letermovir prophylaxis reduced cytomegalovirus reactivation and resistance post umbilical cord blood transplantation. Br J Haematol 2024 (Online ahead of print). doi: 10.1111/bjh.19451.