The purpose of this study is to determine if favipiravir is effective in reducing the time to resolution of influenza symptoms.

The purpose of this study is to determine if a 5-day regimen of favipiravir reduces the time to alleviation of influenza symptoms, resolution of fever, and viral shedding, in subjects with uncomplicated influenza compared to no treatment (e.g. placebo).

Inclusion Criteria:

• At time of enrollment has 2 or more of the following symptoms (moderate to severe in intensity) that began 48 hours or less prior to the anticipated start of dosing with study medication: cough, sore throat, headache, nasal congestion, body aches and pains, fatigue
• Has a fever at the first visit or in the 6 hours prior if antipyretics were taken, defined as: ≥ 38.0°C (≥ 100.4°F) if < 65 years old; or ≥ 37.8°C (≥ 100.0°F) if ≥ 65 years old
• Tests positive for influenza A or B during the 48 hours between onset of symptoms and anticipated dosing with study medication as confirmed by RAT or PCR testing (study or non-study procedure); or per Investigator and Medical Monitor discretion in the event there is a known influenza outbreak circulating in the community or the subject has been in close contact with a person who was recently confirmed to have laboratory-confirmed influenza
• Willing to adhere to strict contraceptive measures throughout study and for 3 months following last dose of study medication

Exclusion Criteria:

• Female subjects who are pregnant, currently breast-feeding, or have a positive pregnancy test at Screening
• Has taken an anti-influenza drug, or received any live attenuated influenza vaccine within 4 weeks prior to signing the informed consent
• Has underlying chronic respiratory disease; includes bronchial asthma if currently experience asthma symptoms, requires current asthma treatment, or has had an asthma attack in the past year
• Is suspected of having bacterial respiratory infection (i.e., expectoration of purulent or mucopurulent sputum and/or infiltrate in lung observed on chest x ray, or is on antibiotics for pulmonary disease) at start of study
• Has a history of gout or is under treatment for: gout or hyperuricemia; hereditary xanthinuria; hypouricemia or xanthine calculi of the urinary tract
• Has a history of hypersensitivity to an anti-viral nucleoside-analog drug targeting a viral RNA polymerase
• Current use of adrenocorticosteroids (except topical preparation) or immunosuppressive drugs
• Has an allergy or contraindication to use of acetaminophen (paracetamol)
• Has a serious chronic disease, history of alcohol or drug abuse within preceding 2 years, psychiatric illness not well controlled (not on stable regimen > 1 year), or is deemed by the Investigator to be ineligible for any reason
• Previously participated in a clinical trial of favipiravir (T-705)
• Has renal insufficiency requiring hemodialysis or continuous ambulatory peritoneal dialysis (CAPD)