Can an antiviral drug stop RSV in vulnerable patients?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * 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) * Receiving treatment for a refractory or relapsed hematologic malignancy, or received a hematopoietic cell transplant (HCT), chimeric antigen receptor T cell therapy (CARTx), or bispecific antibody (bsAb) therapy within the past 365 days (relative to RSV diagnosis date) * Categorized as moderate-risk (overall score 3-6) or high-risk (overall score 7-10) 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) 93% 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 ≥ 93%) 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 Exclusion Criteria: * Received or receiving an approved or authorized direct-acting antiviral therapy with potential efficacy against RSV (e.g. ribavirin) for ≥ 24 hours within the prior 7 days, and/or expected to receive anti-RSV direct-acting antiviral therapies for RSV during the course of the study at the time of screening * Received or receiving investigational direct-acting antiviral therapies against RSV for the current RSV episode * Received any investigational anti-RSV monoclonal antibodies or off-label use of approved anti-RSV monoclonal antibodies within \< 4 months or \< 5 half-lives, whichever is longer, before screening, or expected to receive anti-RSV monoclonal antibodies during the course of the study at the time of screening * Received an RSV vaccine after cellular therapy or after starting the current antitumor therapeutic regimen * Participation in any other concurrent clinical trial of an experimental treatment for RSV, including RSV vaccines * Alanine aminotransferase (ALT) ≥ 5 times the upper limit of normal within 7 days prior to screening * Unable to tolerate nasal sampling required for this study, as determined by the investigator (e.g., history of significant epistaxis, nasopharyngeal anatomical abnormalities, nasal or sinus surgery) * A life expectancy of three months or less, as determined by the investigator * Pregnant, as determined by a Point-of-Care urine pregnancy test or reported by the patient or their electronic health record within 7 days of screening * Receiving, requiring, or expected to require supplemental oxygen for RSV-related illness or SpO2 \< 93% at rest \< 24 hours prior to study drug administration * Previous infection or treatment for RSV, or previous treatment or hospitalization for another respiratory viral infection, \< 28 days before screening * Documented positive test for other respiratory viruses concomitantly (limited to influenza, parainfluenza, adenovirus, human metapneumovirus, or coronavirus \[including SARS-CoV-2\]) ≤ 7 days prior to screening, as determined by local testing (additional testing not required) * Clinically significant bacteremia or fungemia ≤ 7 days prior to screening and not adequately treated, as determined by the investigator * Clinically significant bacterial, fungal, or viral pneumonia within two (2) weeks prior to screening and not adequately treated, as determined by the investigator * Clinically significant symptoms of CRS or ICANS within the prior 72 hours before screening that is not adequately controlled, as determined by the investigator * Any inability to take study drug or comply with study procedures that, in the opinion of the investigator, would make the participant unsuitable for the study * Known hypersensitivity or allergy to the study drug, its metabolites, or formulation excipients