The primary objective of this study is to evaluate the effect of presatovir on respiratory syncytial virus (RSV) viral load in autologous or allogeneic hematopoietic cell transplant (HCT) recipients with an acute RSV upper respiratory tract infection (URTI), the effect of presatovir on development of lower respiratory tract complication, being free of any supplemental oxygen progression to respiratory failure, and pharmacokinetics (PK), safety, and tolerability of presatovir.

Inclusion Criteria:

• Received an autologous or allogeneic HCT using any conditioning regimen
• Documented to be RSV-positive as determined by local testing (eg, polymerase chain reaction, direct fluorescence antibody, respiratory viral panel assay, or culture) using an upper respiratory tract sample collected ≤ 6 days prior to Day 1
• New onset of at least 1 of the following respiratory symptoms for ≤ 7 days prior to Day 1: nasal congestion, runny nose, cough, or sore throat, or worsening of one of these chronic (associated with a previously existing diagnosis, eg, chronic rhinorrhea, seasonal allergies, chronic lung disease) respiratory symptoms ≤ 7 days prior to Day 1
• No evidence of new abnormalities consistent with lower respiratory tract infection (LRTI) on a chest X-ray relative to the most recent chest X-ray, as determined by the local radiologist. If a chest X-ray is not available or was not obtained during standard care < 48 hours prior to screening, a chest X-ray must be obtained for screening
• O2 saturation ≥ 92% on room air
• An informed consent document signed and dated by the participant or a legal guardian of the participant and the investigator or his/her designee
• A negative urine or serum pregnancy test is required for female participants (unless surgically sterile or greater than two years post-menopausal)
• Male and female participants of childbearing potential must agree to contraceptive requirements as described in the study protocol
• Willingness to complete necessary study procedures and have available a working telephone or email

Exclusion Criteria:

Related to concomitant or previous medication use:

• Use of non-marketed (according to region) investigational agents within 30 days, OR use of any monoclonal anti-RSV antibodies within 4 months or 5 half-lives of screening, whichever is longer, OR use of any investigational RSV vaccines after HCT

Related to medical history:

• Pregnant, breastfeeding, or lactating females
• Unable to tolerate nasal sampling required for this study, as determined by the investigator
• Known history of HIV/AIDS with a CD4 count <200 cells/μL within the last month
• History of drug and/or alcohol abuse that, in the opinion of the investigator, may prevent adherence to study activities

Related to medical condition at screening:

• Documented to be positive for other respiratory viruses (limited to influenza, parainfluenza, human rhinovirus, adenovirus, or human metapneumovirus, or coronavirus) within 7 days prior to the screening visit, as determined by local testing (additional testing is not required)
• Clinically significant bacteremia or fungemia within 7 days prior to screening that has not been adequately treated, as determined by the investigator
• Clinically significant bacterial, fungal, or viral pneumonia within 2 weeks prior to screening that has not been adequately treated, as determined by the investigator
• Excessive nausea/vomiting at screening, as determined by the investigator, or an inability to swallow pills that precludes oral administration of the investigational medical product (for participants without an nasogastric tube in place)
• Any condition which, in the opinion of the investigator, would prevent full participation in this trial or would interfere with the evaluation of the trial endpoints

Related to laboratory results:

• Creatinine clearance < 30 mL/min (calculated using the Cockcroft-Gault method)
• Clinically significant aspartate aminotransferase/alanine aminotransferase, as determined by the investigator
• Clinically significant total bilirubin, as determined by the investigator