MK-8228 (Letermovir) Versus Placebo in the Prevention of Clinically-Significant Cytomegalovirus (CMV) Infection in Adult, CMV-Seropositive Allogeneic Hematopoietic Stem Cell Transplant Recipients (MK-8228-001)

Inclusion Criteria:

- Has documented seropositivity for CMV within 1 year before hematopoietic stem cell
transplant (HSCT)

- Receiving first allogeneic HSCT (bone marrow, peripheral blood stem cell, or cord
blood transplant)

- Female or male participant who is not of reproductive potential, or, if of
reproductive potential, agrees to true abstinence or to use (or have their partner
use) 2 acceptable methods of birth control from the time of consent through 90 days
after the last dose of study drug

- Able to read, understand, and complete questionnaires and diaries

Exclusion Criteria:

- Received a previous allogeneic HSCT (previous autologous HSCT is acceptable)

- History of CMV end-organ disease within 6 months before randomization

- Has evidence of CMV viremia (if tested) at any time from either signing of the
Informed Consent Form or the HSCT procedure, whichever is earlier, until the time of
randomization.

- Received the following within 7 days before screening or plans to receive during the
study: ganciclovir, valganciclovir, foscarnet, acyclovir, valacyclovir, or
famciclovir

- Received the following within 30 days before screening or plan to receive during the
study: cidofovir, CMV hyper-immune globulin, any investigational CMV antiviral agent
or biological therapy

- Has suspected or known hypersensitivity to ingredients of MK-8228 (letermovir)
formulations

- Has severe hepatic insufficiency within 5 days before randomization

- Has end-stage renal impairment

- Has an uncontrolled infection on the day of randomization

- Requires mechanical ventilation or is hemodynamically unstable at the time of
randomization

- Has documented positive results for human immunodeficiency virus (HIV) antibody,
hepatitis C virus (HCV) antibody with detectable HCV ribonucleic acid, or hepatitis B
surface antigen (HBsAg) within 90 days before randomization

- Has active solid tumor malignancies with the exception of localized basal cell or
squamous cell skin cancer or the condition under treatment (for example, lymphoma)

- Is pregnant or expecting to conceive, is breastfeeding, or plans to breastfeed from
the time of consent through 90 days after the last dose of study drug

- Is expecting to donate eggs or sperm from the time of consent through 90 days after
the last dose of study drug

- Has participated in a study with an unapproved investigational compound (monoclonal
antibodies are excepted) or device within 28 days of the first dose of study drug

- Has previously participated in a MK-8228 (letermovir) study

- Has, is, or is planning (during the study) to participate in any study involving
administration of a CMV vaccine or another CMV investigational agent

- Is a user of recreational or illicit drugs or has a recent history (<=1 year) of drug
or alcohol abuse or dependence