A Study of Maribavir Pediatric Formulation in Healthy Adult Participants

Inclusion Criteria

• An understanding, ability, and willingness to fully comply with study procedures and restrictions and to voluntarily sign (personally or via a legally authorized representative) informed consent form to participate in the study.
• Age 18 to 55 years, inclusive at the time of consent, at the screening visit.
• Male, or non-pregnant, non-breastfeeding female who agrees to comply with any applicable contraceptive requirements of the protocol or female of non-childbearing potential.
• Body mass index (BMI) between 18.0 and 30.0 kilogram per meter square (kg/m^2), inclusive with a body weight greater than (>) 50 kilograms (kg) (110 pounds [lbs]), at the screening visit.
• Healthy as determined by the Investigator or designee on the basis of screening evaluations and medical history.
• Hemoglobin for males greater than or equal to (>=) 135.0 gram per liter (g/L) and females >=120.0 g/L, at the screening visit and on Day -1 of Treatment Period 1.
• Ability to swallow a dose of maribavir or rabeprazole.

Exclusion Criteria

• History or presence of gastritis, gastrointestinal (GI) tract disorder, hepatic disorder or cholecystectomy, history of treated or untreated Helicobacter pylori, ulcer disease or other clinical condition which, in the opinion of the investigator or designee, may affect the absorption, distribution, metabolism, or elimination of the study drugs.
• History of any hematological, hepatic, respiratory, cardiovascular, renal, neurological or psychiatric disease, gall bladder removal, or current recurrent disease that could affect the action, absorption, or disposition of the study drugs, or clinical or laboratory assessments.
• Current or relevant history of physical or psychiatric illness, any medical disorder that may require treatment or make the participant unlikely to fully complete the study, or any condition that presents undue risk from the study drugs or procedures.
• Known or suspected intolerance or hypersensitivity to maribavir or rabeprazole (Part 2 only), closely related compounds, or any of the stated ingredients and excipients.
• Significant illness, as judged by the Investigator or designee, within 2 weeks of the first dose of the investigational drug (ID).
• Has diarrhea within 4 hours of the first dose of the ID.
• Donation of blood or blood products (example, plasma or platelets) within 60 days prior to receiving the first dose of the ID.
• Within 30 days prior to the first dose of the ID:
• Have used any investigational product (if elimination half-life is less than [ 140 millimeters of mercury (mmHg) or 90 mmHg or 450 millisecond (msec) at the screening visit. If QTc exceeds 450 msec, the ECG should be repeated two more times and the average of the three QTc values should be used to determine the participant's eligibility.
• Known history of alcohol or other substance abuse within the last year.
• Male participants who consume more than 21 units of alcohol per week or three units per day. Female participants who consume more than 14 units of alcohol per week or two units per day (one alcohol unit = one beer or one wine [5 ounces [oz]/150 milliliter [mL]] or one liquor [1.5 oz/40 mL] or 0.75 oz alcohol).
• A positive screen for alcohol or drugs of abuse at the screening visit or on Day -1 of Treatment Period 1. Urine samples are to be tested for amphetamines, barbiturates, benzodiazepines, cannabinoids, cocaine, methadone, opiates, and phencyclidine.
• A positive Human immunodeficiency virus (HIV), Hepatitis B surface antigen (HBsAg), or Hepatitis C virus (HCV) antibody screen at the screening visit.
• Use of tobacco in any form (example, smoking or chewing) or other nicotine-containing products in any form (example, gum, patch). Ex-users must self-report that they have stopped using tobacco for at least 3 months prior to receiving the first dose.
• Routine consumption of more than two units of caffeine per day or participants who experience caffeine withdrawal headaches (O