Study of S-033188 (Baloxavir Marboxil) Compared With Placebo or Oseltamivir in Patients With Influenza at High Risk of Influenza Complications

Inclusion Criteria:

1. Patients or their legal guardians who provide written informed consent to participate
in the study on a voluntary basis. For adolescent patients, informed consent/assent of
voluntary participation should be obtained in accordance with local requirements.

2. Male or female patients ≥ 12 years at the time of signing the informed consent/assent
form.

3. Patients with a diagnosis of influenza confirmed by all of the following:

1. Fever ≥ 38ºC (axillary) during the predose examinations or within the 4 hours
prior if antipyretics were taken

2. A positive rapid influenza diagnostic test (RIDT) result OR A patient with a
negative RIDT may be enrolled if the patient reports contact with a known case of
influenza within the prior 7 days and all other inclusion criteria are met.

3. At least 1 each of the following general and respiratory symptoms associated with
influenza is present with a severity of moderate or greater:

i. General symptoms (headache, feverishness or chills, muscle or joint pain, or
fatigue) ii. Respiratory symptoms (cough, sore throat, or nasal congestion)

4. The time interval between the onset of symptoms and the predose examinations is 48
hours or less. The onset of symptoms is defined as either:

1. Time of the first increase in body temperature (an increase of at least 1ºC from
normal body temperature)

2. Time when the patient experiences at least 1 new general or respiratory symptom

5. If a women of childbearing potential, agrees to use a highly effective method of
contraception for 3 months after the first dose of study drug

6. Patients will be considered at high risk* of influenza complications due to the
presence of at least 1 of the following inclusion criteria:

1. Asthma or chronic lung disease (such as chronic obstructive pulmonary disease or
cystic fibrosis)

2. Endocrine disorders (including diabetes mellitus)

3. Residents of long-term care facilities (eg, nursing homes)

4. Compromised immune system (including patients receiving corticosteroids not
exceeding 20 mg of prednisolone or equivalent, and patients being treated for
human immunodeficiency virus [HIV] infection with a CD4 count > 350 cells/mm³
within the last 6 months)

5. Neurological and neurodevelopmental disorders (including disorders of the brain,
spinal cord, peripheral nerve, and muscle, eg, cerebral palsy, epilepsy [seizure
disorders], stroke, muscular dystrophy, or spinal cord injury)

6. Heart disease (such as congenital heart disease, congestive heart failure, or
coronary artery disease), excluding hypertension without any other heart-related
symptoms

7. Adults aged ≥ 65 years

8. American Indians and Alaskan Natives

9. Blood disorders (such as sickle cell disease)

10. Metabolic disorders (such as inherited metabolic disorders and mitochondrial
disorders)

11. Morbid obesity (body mass index ≥ 40 kg/m²)

12. Women who are within 2 weeks postpartum and are not breastfeeding

Exclusion Criteria:

1. Patients with severe influenza virus infection requiring inpatient treatment.

2. Patients with known allergy to oseltamivir (Tamiflu®).

3. Patients unable to swallow tablets or capsules.

4. Patients who have previously received Baloxavir Marboxil.

5. Patients weighing ≤ 40 kg.

6. Patients who have been exposed to an investigational drug within 30 days prior to the
predose examinations.

7. Women who are pregnant, breastfeeding, or have a positive pregnancy test at the
predose examinations. The following female patients who have documentation of either a
or b below do not need to undergo a pregnancy test at the predose examinations:

1. Postmenopausal women (defined as cessation of regular menstrual periods for 2
years or more and confirmed by a follicle-stimulating hormone test)

2. Women who are surgically sterile by hysterectomy, bilateral oophorectomy, or
tubal ligation

8. Patients with concurrent infections at the predose examinations requiring systemic
antimicrobial therapy.

9. Patients with liver disease associated with hepatic impairment.

10. Patients with cancer within the last 5 years (unless nonmelanoma skin cancer).

11. Patients with untreated HIV infection or treated HIV infection with a CD4 count below
350 cells/mm3 in the last 6 months.

12. Patients with immunosuppression following organ or bone marrow transplants.

13. Patients exceeding 20 mg of prednisolone or equivalent dose of chronic systemic
corticosteroids.

14. Patients who have received peramivir, laninamivir, oseltamivir, zanamivir,
rimantadine, umifenovir or amantadine within 30 days prior to the predose
examinations.

15. Patients who have received an investigational monoclonal antibody for a viral disease
in the last year.

16. Patients with known creatinine clearance ≤ 60 mL/min.

17. Patients who, in the opinion of the investigator, would be unlikely to comply with
required study visits, self-assessments, and interventions