Severe Influenza Trial of ARbidol

Inclusion Criteria: 1. Hospitalized males or females with a positive antigen or PCR test for influenza virus infection 2. Age ≥16 years at the time of signing Informed Consent Form 3. Arterial oxygen saturation (SaO2)/ pulse oxygen saturation (SPO2) ≤94% in room air condition 4. ≤ 7 days since symptom onset. The onset of symptoms is defined as either: Time of the first increase in body temperature (an increase of at least 1ºC from normal body temperature- ≥38℃); Time when the patient experiences at least one general or respiratory symptom. 5. Willingness to use contraception for 7 days after the end of treatment Exclusion Criteria: 1. Physicians make a decision that trial involvement is not in patients' best interest, or any condition that does not allow the protocol to be followed safely. 2. Patient refusal to accept invasive organ support treatment if needed 3. More than 3 consecutive doses of NAIs within 2 days before enrolment (including oseltamivir, zanamivir, peramivir) 4. Women who are pregnant (including a positive pregnancy test at enrolment), breastfeeding, or within 2 weeks post-partum. The following female subjects do not need to undergo a pregnancy test at enrolment: a. Postmenopausal (defined as cessation of regular menstrual periods for 2 years or more and confirmed by a follicle-stimulating hormone test) women. b. Women who are surgically sterile by hysterectomy, bilateral oophorectomy, or tubal ligation. 5. Any condition requiring renal replacement therapy 6. Severe liver disease (Child-Pugh score ≥ C) 7. A history of hypersensitivity to arbidol or oseltamivir (Tamiflu®) 8. Currently or have been involved in another anti-influenza treatment trial in the last 28 days 9. Patients who, in the opinion of the investigator, would be unlikely to comply with required study visits, self-assessments, and interventions