Please refer to protocol section 3 for information on study objectives.

Overall objectives include:

Objective 1: Determine the efficacy of letermovir for preventing CMV infection in thoracic organ transplant recipients as compared to valganciclovir prophylaxis

Objective 2: Determine the tolerability of letermovir for CMV prophylaxis among heart and lung transplant recipients as compared to valganciclovir Please refer to protocol section 3 for information on study objectives.

Objective 1: The primary outcome will be CMV infection (CMV viremia with CMV viral load greater than 1,000, CMV syndrome, or tissue invasive CMV disease) during the planned prophylaxis period and the following 180 days.

Objective 2: The primary outcome will be the proportion of days during which appropriately-dosed prophylaxis was received during the planned treatment course. Please refer to protocol section 3 for information on study objectives.

Objective 1: Secondary outcomes will include the proportion of subjects who develop the following during the planned prophylaxis period and the following 180 days:

1.      Biopsy-proven acute cellular rejection 
2.      CMV resistance will be determined by the presence of a clinical significant mutation on genomic sequencing9 

Objective 2: Secondary outcomes will include the proportion of subjects who develop the following during the planned prophylaxis period:

1.      Neutropenia (absolute neutrophil count (ANC) less than 1,500/microliter)
2.      Severe thrombocytopenia (platelet count less than 50,000/microliter)
3.      Unplanned discontinuation of MMF or azathioprine
4.      Incorrect renal dosing at any point during the planned prophylaxis period (measured as a binary variable, where the outcome is met if the recipient receives any days of incorrect dosing per their GFR)

You may be eligible for this study if you meet the following criteria:

• Conditions: Medical Research
• Age: 99 years or below
• Gender: All