Infections with human herpesvirus 6 variant B delay platelet engraftment after allogeneic haematopoietic stem cell transplantation

Summary The clinical significance of human herpesvirus (HHV‐6) infections after allogeneic stem cell transplantation (SCT) remains controversial. We analysed cryoconserved plasma samples from 82 patients after allogeneic SCT by quantitative polymerase chain reaction for HHV‐6 variants A and B. Platelet engraftment was delayed in patients with HHV‐6B infections but not with HHV‐6A infections detected before day +28. In multivariate analysis early HHV‐6B infections and the type of conditioning were associated with platelet engraftment. In conclusion, the two variants of HHV‐6 should be studied separately; early infections with HHV‐6B may contribute to delayed platelet engraftment after allogeneic SCT.