Table 1 Inclusion and exclusion criteria

Inclusion criteria

Age 6 to < 12 years

Body weight ≥ 10 kg

Diagnosed with influenza infection defined as:

Fever (axillary temperature ≥ 38 °C)

 A positive RIDT by nasopharyngeal swab, pharyngeal swab, or nasal discharge

 At least one moderate or severe respiratory symptom (cough and nasal discharge/nasal congestion)

 Onset of first confirmed fever (≥ 37.5 °C) no more than 48 h before screening (Day 1)

Judged by the investigator as able to take baloxavir tablet(s) and oseltamivir capsules or dry syrup

Where possible, written informed assent from children

Written informed consent from a parent or legal guardian

Parents/guardians willing and able to comply with the trial requirements

Patients who can comply with the trial requirements to the level of their understanding

Exclusion criteria

Severe influenza symptoms requiring hospitalization

Risk factors for influenza infection including:

 Chronic respiratory diseases including uncontrolled bronchial asthma

 Hepatitis, liver cirrhosis

 Neurological disorders and neurodevelopmental disorders including brain, spinal, peripheral, and muscle disorders

 Endocrine disorders including diabetes, thyroid disease, and adrenal gland abnormalities

 Heart disease requiring drug treatment including congenital heart disease, congestive heart failure, and coronary artery disease

Receiving systemic corticosteroids or immunosuppressive therapy

Primary immunodeficiency syndrome

Severe renal impairment (creatinine clearance < 30 mL/min or eGFR < 30 mL/min/1.73 m²)

Human immunodeficiency virus infection

Malignant disease within the past 5 years

Disorders of consciousness including abnormal behavior^a and convulsions, and complicated by encephalitis/encephalopathy

History of encephalitis/encephalopathy or epilepsy not controlled with antiepileptic drugs or abnormal behavior^a associated with influenza infection in the past 2 years

Infectious diseases requiring systemic antimicrobial therapy and/or antiviral medicine (except anti-influenza medicine) at screening

Considered by the investigator to be using prohibited drugs

Receiving baloxavir, amantadine, or NAIs (oseltamivir, zanamivir, peramivir, and laninamivir) within 30 days before screening

History of allergies to anti-influenza drugs, or acetaminophen, or clinically problematic intolerance

Positive SARS-CoV-2 or suspected COVID-19 disease

Any underlying disease that may affect study outcomes

Difficulty collecting blood from a vein

Patients received an investigational or unapproved drug within 30 days or 5 half-lives, whichever is longer, before screening

Patients with diseases or conditions which, in the opinion of the investigator, may make it difficult to ensure patient safety or study data quality

Patients who, in the opinion of the investigator, are inappropriate for participation in the study

Female patients who has experienced menarche and who are pregnant, plan to become pregnant during the study period, or are breastfeeding