Inclusion Criteria:  Presented to the healthcare facility with symptoms suggestive of a diagnosis of acute respiratory syncytial virus (RSV) infection Has at least 2 symptoms of lower respiratory tract disease (LRTD), one of which must be scored as at least 'moderate' if the symptoms did not pre-exist before RSV onset, or one of which is scored worse than usual if the symptoms pre-existed Tested positive for RSV infection using a molecular-based diagnostic assay (polymerase chain reaction [PCR] or other) on a bilateral nasal mid-turbinate swab sample Has at least one of the following high-risk conditions that predispose them to RSV-related disease progression: a. age greater than or equal to (>=) 65 years, b. congestive heart failure (CHF), c. chronic obstructive pulmonary disease (COPD), d. asthma Randomized to study intervention treatment within 72 hours after onset of any of the RSV symptoms or worsening of pre-existing symptoms Not be hospitalized during screening (emergency room or hospital observation status for an anticipated duration of less than [<] 24 hours are not considered as hospitalization)  Exclusion Criteria:  Known allergies, hypersensitivity, or intolerance to rilematovir or to any of the excipients of rilematovir or placebo formulation Presence of clinically significant heart arrhythmias, uncontrolled, unstable atrial arrhythmia, or sustained ventricular arrhythmia Participant has known or suspected (from medical history or participant examination) chronic or acute hepatitis B or C infection Immunocompromised conditions Living in institutional care or assisted living facility and also receiving acute care management for any respiratory condition