<p>Pediatric liver transplant recipients are often transplanted at a young age, precluding them from receiving live virus vaccinations (LVV) such as varicella (VZV) vaccine and measles, mumps and rubella (MMR). This places them at profound risk for vaccine preventable illness. We sought to detail safety of vaccination. This was a retrospective cohort study of pediatric liver transplant recipients at two children's hospitals.&nbsp;Among 204 liver transplant recipients included in the study, 97 received at least one LVV after liver transplant. Six patients who did not receive LVV after transplant had evidence of vaccine-preventable infection following vaccination (1 disseminated VZV disease, 5 VZV-related rash), while one patient who received LVV after transplant developed a diffuse VZV-related rash. Rejection rates were the same between those that did and did not receive a live virus vaccine post-transplant. There were no serious adverse events caused by vaccination post-transplant.&nbsp;Live virus vaccination following liver transplant was safe at our two institutions, although there exist limitations in our study due to its retrospective study design. Larger scale studies should be performed to evaluate the effectiveness of LVV in relation to immunosuppression.</p>

<p><strong>BACKGROUND: </strong>Cytomegalovirus (CMV) is a significant source of morbidity and mortality among transplant recipients; the epidemiology is less understood in pediatric hematopoietic cell transplantation (HCT) cohorts. Furthermore, there is a paucity of data related to CMV prophylactic and preemptive strategies.</p>

<p><strong>METHODS: </strong>A single-center retrospective observational cohort of allogeneic HCT recipients at the Children's Hospital of Philadelphia January 1, 2004-December 31, 2017 was constructed. Subjects were followed for 180 days after transplant to determine whether they had CMV infection or disease. Data on antiviral therapy were collected as were outcomes of CMV disease and adverse events (AEs) related to the antiviral therapy.</p>

<p><strong>RESULTS: </strong>Between January 2004 and March 2017, 345 allogeneic HCTs in 333 patients undergoing CMV surveillance testing were identified. CMV DNAemia was detected during the 180-day follow-up in 89 (25.8%) HCTs. CMV recipient-positive transplants were most likely to have CMV infection (47%). Infection rates were high for those receiving a CMV-specific prophylaxis regimen (50%). CMV DNAemia progressed to CMV disease 11.2% of the time. Of 224 subjects receiving CMV-specific prophylaxis, 19.2% experienced ≥1 AE. Of 53 receiving preemptive therapy during any CMV DNAemia episode, 32.1% experienced ≥1 AE.</p>

<p><strong>CONCLUSIONS: </strong>CMV infection is common in pediatric allogeneic HCT recipients. The CMV-specific prophylaxis regimen employed in this cohort did not effectively prevent DNAemia, progression to CMV disease was uncommon, and AEs from prophylaxis and preemptive therapy were frequent. Novel approaches that reduce the impact of CMV on pediatric allogeneic HCT recipients are needed.</p>