<br>        Inclusion Criteria:<br><br>          1. Patients or their legal guardians who provide written informed consent to participate<br>             in the study on a voluntary basis. For adolescent patients, informed consent/assent of<br>             voluntary participation should be obtained in accordance with local requirements.<br><br>          2. Male or female patients = 12 years at the time of signing the informed consent/assent<br>             form.<br><br>          3. Patients with a diagnosis of influenza confirmed by all of the following:<br><br>               1. Fever = 38ºC (axillary) during the predose examinations or within the 4 hours<br>                  prior if antipyretics were taken<br><br>               2. A positive rapid influenza diagnostic test (RIDT) result OR A patient with a<br>                  negative RIDT may be enrolled if the patient reports contact with a known case of<br>                  influenza within the prior 7 days and all other inclusion criteria are met.<br><br>               3. At least 1 each of the following general and respiratory symptoms associated with<br>                  influenza is present with a severity of moderate or greater:<br><br>             i. General symptoms (headache, feverishness or chills, muscle or joint pain, or<br>             fatigue) ii. Respiratory symptoms (cough, sore throat, or nasal congestion)<br><br>          4. The time interval between the onset of symptoms and the predose examinations is 48<br>             hours or less. The onset of symptoms is defined as either:<br><br>               1. Time of the first increase in body temperature (an increase of at least 1ºC from<br>                  normal body temperature)<br><br>               2. Time when the patient experiences at least 1 new general or respiratory symptom<br><br>          5. If a women of childbearing potential, agrees to use a highly effective method of<br>             contraception for 3 months after the first dose of study drug<br><br>          6. Patients will be considered at high risk* of influenza complications due to the<br>             presence of at least 1 of the following inclusion criteria:<br><br>               1. Asthma or chronic lung disease (such as chronic obstructive pulmonary disease or<br>                  cystic fibrosis)<br><br>               2. Endocrine disorders (including diabetes mellitus)<br><br>               3. Residents of long-term care facilities (eg, nursing homes)<br><br>               4. Compromised immune system (including patients receiving corticosteroids not<br>                  exceeding 20 mg of prednisolone or equivalent, and patients being treated for<br>                  human immunodeficiency virus [HIV] infection with a CD4 count > 350 cells/mm³<br>                  within the last 6 months)<br><br>               5. Neurological and neurodevelopmental disorders (including disorders of the brain,<br>                  spinal cord, peripheral nerve, and muscle, eg, cerebral palsy, epilepsy [seizure<br>                  disorders], stroke, muscular dystrophy, or spinal cord injury)<br><br>               6. Heart disease (such as congenital heart disease, congestive heart failure, or<br>                  coronary artery disease), excluding hypertension without any other heart-related<br>                  symptoms<br><br>               7. Adults aged = 65 years<br><br>               8. American Indians and Alaskan Natives<br><br>               9. Blood disorders (such as sickle cell disease)<br><br>              10. Metabolic disorders (such as inherited metabolic disorders and mitochondrial<br>                  disorders)<br><br>              11. Morbid obesity (body mass index = 40 kg/m²)<br><br>              12. Women who are within 2 weeks postpartum and are not breastfeeding<br><br>        Exclusion Criteria:<br><br>          1. Patients with severe influenza virus infection requiring inpatient treatment.<br><br>          2. Patients with known allergy to oseltamivir (Tamiflu®).<br><br>          3. Patients unable to swallow tablets or capsules.<br><br>          4. Patients who have previously received baloxavir marboxil.<br><br>          5. Patients weighing = 40 kg.<br><br>          6. Patients who have been exposed to an investigational drug within 30 days prior to the<br>             predose examinations.<br><br>          7. Women who are pregnant, breastfeeding, or have a positive pregnancy test at the<br>             predose examinations. The following female patients who have documentation of either a<br>             or b below do not need to undergo a pregnancy test at the predose examinations:<br><br>               1. Postmenopausal women (defined as cessation of regular menstrual periods for 2<br>                  years or more and confirmed by a follicle-stimulating hormone test)<br><br>               2. Women who are surgically sterile by hysterectomy, bilateral oophorectomy, or<br>                  tubal ligation<br><br>          8. Patients with concurrent infections at the predose examinations requiring systemic<br>             antimicrobial therapy.<br><br>          9. Patients with liver disease associated with hepatic impairment.<br><br>         10. Patients with cancer within the last 5 years (unless nonmelanoma skin cancer).<br><br>         11. Patients with untreated HIV infection or treated HIV infection with a CD4 count below<br>             350 cells/mm3 in the last 6 months.<br><br>         12. Patients with immunosuppression following organ or bone marrow transplants.<br><br>         13. Patients exceeding 20 mg of prednisolone or equivalent dose of chronic systemic<br>             corticosteroids.<br><br>         14. Patients who have received peramivir, laninamivir, oseltamivir, zanamivir,<br>             rimantadine, umifenovir or amantadine within 30 days prior to the predose<br>             examinations.<br><br>         15. Patients who have received an investigational monoclonal antibody for a viral disease<br>             in the last year.<br><br>         16. Patients with known creatinine clearance = 60 mL/min.<br><br>         17. Patients who, in the opinion of the investigator, would be unlikely to comply with<br>             required study visits, self-assessments, and interventions<br>