A Clinical Study of Letermovir (MK-8228) in Children and Adolescents Who Receive a Kidney Transplant (KT) (MK-8228-077)

Inclusion Criteria:

The main inclusion criteria include but are not limited to the following:

* Is a recipient of a primary or secondary allograft kidney
* Is at least 4 weeks posttransplant and not more than 52 weeks posttransplant at the time of enrollment (Day 1) and is being managed per local standard of care
* Has stable kidney function posttransplant
* Has undetectable CMV deoxyribonucleic acid (DNA) from a plasma or whole blood sample collected within 14 days prior to enrollment
* Must be able to take (as assessed by the investigator) letermovir tablets or oral pellets by mouth, or via gastrostomy or nasogastric tube (oral pellets only)
* Does not have a condition that may interfere with the absorption of oral medication (e.g., vomiting, diarrhea, or a malabsorptive condition) from the day of enrollment (Day 1) until the intensive pharmacokinetics (IPK) sampling is completed
* Weighs ≥2.5 and \<40 kg at enrollment (Day 1)

Exclusion Criteria:

The main exclusion criteria include but are not limited to the following:

* Has CMV disease or suspected CMV disease between screening and enrollment
* Is on dialysis or plasmapheresis at the time of enrollment
* Has evidence of CMV viremia at any time from screening until the time of enrollment
* Has Child-Pugh B or C hepatic insufficiency within 14 days before enrollment
* Is a multi-organ transplant recipient (e.g., kidney-pancreas)
* Has any uncontrolled infection on the day of enrollment
* Requires mechanical ventilation, or is hemodynamically unstable, at the time of enrollment
* Has received or is receiving protocol-specified prohibited medications