• Aged ≥ 18 years

• Willing and able to provide written informed consent, or with a legal representative who can provide informed consent (where locally approved)

• RSV confirmed by local lab testing via nucleic acid amplification test (e.g. polymerase chain reaction \[PCR\] or respiratory viral panel \[RVP\]) using an upper respiratory tract sample collected within the 5 days prior to day 1 (RDV dosing)

• Symptomatic RSV infection of the upper respiratory tract, with symptom onset and positive microbiologic testing within the 5 days prior to day 1 (RDV dosing). Symptomatic RSV infection is defined as having new upper respiratory symptom(s) or worsening of a pre-existing upper respiratory symptom (if chronic and associated with a previously existing diagnosis, such as chronic lung disease, chronic rhinorrhea, or seasonal allergies)

• Have one of the following underlying diseases and/or received one of the following treatments relative to RSV diagnosis date:

‣ Received allogeneic hematopoietic cell transplant (HCT) with any conditioning regimen within 1 year

⁃ Received autologous HCT with any conditioning regimen within 3 months

⁃ Received Chimeric antigen receptor T cell therapy (CARTx) within 3 months

⁃ Have multiple myeloma (MM) and received bispecific antibody therapy (bsAb) within 3 months

⁃ Have lymphoma and received bsAb within 3 months

• Categorized as moderate-risk (overall score 3-6) or high-risk (overall score 7-12) per an adapted version of the Immunodeficiency Scoring Index (ISI) for RSV, as below, relative to the day of RSV diagnosis:

‣ 1 point:

• Recent (within the prior 30 days) allogeneic HCT, autologous HCT, or CARTx

∙ Corticosteroids within the prior 30 days for management of graft versus host disease (GVHD) or cytokine release syndrome (CRS) or immune effector cell-associated neurotoxicity syndrome (ICANS).

⁃ 2 points:

• Age ≥ 40 years

⁃ 3 points:

• Absolute neutrophil count (ANC) \< 500 cells/μL within the prior 7 days

∙ Absolute lymphocyte count (ALC) \< 200 cells/µL within the prior 7 days

• Oxygen saturation (SpO2) 92% or greater on room air and at rest (to be measured after participant has rested in a quiet room for ≥ 2 minutes, with oxygen \[O2\] saturation probe on finger or earlobe for ≥ 1 minute, with saturation reading remaining ≥ 92%) at screening

• Willingness to take study drug and complete necessary study procedures

• Participants of childbearing potential who engage in heterosexual intercourse must agree to use protocol-specified method(s) of contraception as described