The primary objective of this study is to evaluate the effect of presatovir on nasal respiratory syncytial virus (RSV) viral load in RSV-positive lung transplant (LT) recipients with acute respiratory symptoms.

Key Inclusion Criteria:

• Males and females ≥18 years of age who have received a LT (single or double) or heart/lung transplant > 90 days prior to Screening
• Confirmed to be RSV-positive by local polymerase chain reaction (PCR) testing (starting from when the upper or lower respiratory tract sample is obtained) ≤ 7 days prior to investigational medicinal product (IMP) administration on Day 1/Baseline
• New onset or acute worsening, if the symptom is chronic, of at least 1 of the following respiratory symptoms ≤ 7 days prior to IMP administration on Day 1/Baseline: nasal congestion, earache, runny nose, cough, sore throat, shortness of breath, or wheezing
• A negative local urine or serum pregnancy test for female subjects of childbearing potential at Screening, within 1 day prior to IMP administration. When available, existing local pregnancy test results obtained prior to Screening may be used, provided the testing was completed within 1 day prior to IMP administration
• Agreement from male and female subjects of childbearing potential who engage in heterosexual intercourse to use protocol specified method(s) of contraception

Key Exclusion Criteria:

Related to concomitant or previous medication use:

• Use of any non-marketed (according to region) investigational agents within 30 days, OR use of any investigational monoclonal anti-RSV antibodies within 4 months or 5 half-lives of Screening, whichever is longer, OR use of any prior investigational RSV vaccines
• Use of a strong or moderate cytochrome P450 enzyme (CYP) inducer including but not limited to rifampin, St. John's Wort, carbamazepine, phenytoin, efavirenz, bosentan, etravirine, modafinil, and nafcillin, within 2 weeks prior to the first dose of IMP

Related to transplant history:

• Recipient of any other organ transplant prior to Screening, with the exception of a LT (single or double) or heart/lung transplant

Related to medical condition at Screening:

• Known viral coinfection (including but not limited to influenza, metapneumovirus, human rhinovirus, parainfluenza, cytomegalovirus, or coronavirus) in the upper or lower respiratory tract ≤ 14 days prior to Screening unless discussed with the medical monitor and deemed acceptable
• Active systemic infection or infectious pneumonia of any etiology (ie, bacterial, viral [other than RSV] or fungal), including aspiration pneumonia, that is considered clinically significant by the investigator unless discussed with the medical monitor and deemed acceptable

Related to laboratory values:

• Clinically significant kidney dysfunction as defined by: An estimated glomerular filtration rate (eGFR) < 30 mL/min/1.73 m2 as calculated by the Modification of Diet in Renal Disease (MDRD) study 4 parameter equation obtained from screening laboratory measurements or via local laboratory measurements obtained ≤ 7 days prior to Screening. The eGFR may be manually calculated or the reported eGFR value may be used, but any automatically calculated eGFR must be calculated using the MDRD equation.
• Clinically significant liver function test abnormalities as defined by an alanine aminotransferase (ALT) or aspartate aminotransferase (AST) > 5 times the upper limit of normal (ULN) obtained in screening laboratory measurements or via local laboratory measurements obtained ≤ 7 days prior to Screening
• Clinically significant elevations in total bilirubin (TB), as determined by the investigator

Note: Other protocol defined Inclusion/ Exclusion criteria may apply.