Inclusion Criteria:
* Participants must meet all of the following criteria:
The participant or the participant's legally authorized representative understands the study and voluntarily signs the informed consent form. The participant must be 18 to 64 years of age, inclusive, at the time of informed consent.
At screening, the participant meets all of the following criteria:
Positive result from a rapid influenza diagnostic test (antigen test) or polymerase chain reaction (PCR) test.
Axillary temperature of at least 37.3°C at screening. If an antipyretic has been taken, the axillary temperature must be at least 37.3°C at least 4 hours after administration.
At least one influenza-related systemic symptom of moderate or greater severity: muscle or joint pain, fatigue, headache, or feverishness/chills.
At least one influenza-related respiratory symptom of moderate or greater severity: nasal congestion, sore throat, or cough.
The interval between the onset of the first influenza symptom and initiation of study treatment is no more than 48 hours. Symptom onset is defined as either:
The first occurrence of a temperature of at least 37.3°C measured axillary, 37.5°C measured orally, or 38.0°C measured rectally or tympanically; or The onset of at least one systemic or respiratory symptom: nasal congestion, sore throat, cough, muscle or joint pain, fatigue, headache, or feverishness/chills.
The participant is able to comply with all study procedures and complete the participant diary as required.
A female participant must meet either of the following criteria:
Not of childbearing potential, defined as having undergone hysterectomy or bilateral oophorectomy, having medically documented ovarian failure, or being postmenopausal. Postmenopausal status is defined as age greater than 50 years with amenorrhea for at least 12 months; or Of childbearing potential, with a negative pregnancy test at screening, and not pregnant, in the peripartum period, or breastfeeding.
The participant and the participant's partner agree to remain completely abstinent or use effective contraception from screening through 3 months after completion of study treatment. Acceptable methods include:
For a female participant or the female partner of a male participant, one of the following methods together with correct condom use by the male partner: an intrauterine device with an annual failure rate of less than 1%, a female barrier method consisting of a cervical cap or diaphragm with spermicide, or tubal sterilization; or Prior vasectomy of the male participant or the male partner of a female participant.
Male participants agree not to donate sperm from screening through 3 months after completion of study treatment.
Exclusion Criteria:
* Participants meeting any of the following criteria will be excluded:
* Influenza requiring hospitalization, as indicated by any of the following:
* Severe influenza characterized by one or more of the following:
* Persistent fever accompanied by severe cough, purulent sputum, bloody sputum, or chest pain.
* Tachypnea, difficulty breathing, or cyanosis of the lips.
* Altered mental status, including reduced responsiveness, somnolence, or agitation, or the occurrence of seizures.
* Severe vomiting or diarrhea with evidence of dehydration.
* Pneumonia.
* Marked exacerbation of a pre-existing underlying disease.
* Any other clinical condition requiring hospitalization.
* Critical influenza characterized by one or more of the following:
* Respiratory failure.
* Acute necrotizing encephalopathy.
* Shock.
* Multiple organ dysfunction.
* Any other serious clinical condition requiring intensive monitoring or care.
* High risk of severe influenza, as indicated by any of the following:
* A serious or poorly controlled underlying condition, such as chronic pulmonary disease, liver disease, chronic kidney disease, severe hematologic disease, chronic congestive heart failure classified as New York Heart Association functional class III or IV, neurologic or neuromuscular disease, or metabolic disease.
* Clinically significant QT interval abnormality on electrocardiography, defined as a Fridericia-corrected QT interval (QTcF) greater than 450 milliseconds for males or greater than 470 milliseconds for females.
* Immunodeficiency, including malignancy, organ or bone marrow transplantation, human immunodeficiency virus infection, or use of immunosuppressive therapy within the previous 3 months.
* A concomitant condition requiring treatment with aspirin- or salicylate-containing medication.
* Bronchitis, pneumonia, pleural effusion, or interstitial lung abnormality that is clinically suspected or confirmed by chest imaging (posteroanterior or posteroanterior and lateral chest radiography, or computed tomography) at screening and considered clinically significant by the investigator.
* Previous diagnosis of chronic obstructive pulmonary disease, severe allergic rhinitis, or asthma.
* Acute respiratory tract infection, otitis media, or sinusitis within 2 weeks before screening.
* A concomitant infection requiring systemic anti-infective treatment, or a white blood cell count greater than 10.0 × 10\^9/L at screening.
* Purulent sputum or suppurative tonsillitis at screening.
* Suspected hypersensitivity to any active ingredient or excipient of the investigational product or acetaminophen.
* Use of any anti-influenza antiviral medication within 7 days before screening, including but not limited to neuraminidase inhibitors, hemagglutinin inhibitors, M2 ion-channel blockers, or RNA polymerase inhibitors, such as oseltamivir, zanamivir, peramivir, umifenovir (Arbidol), favipiravir, rimantadine, amantadine, baloxavir marboxil, onradivir, suraxavir marboxil, seloxavir marboxil, or pixavir marboxil.
* Receipt of an influenza vaccine within 6 months before screening.
* Suspected or confirmed history of alcohol or drug abuse.
* Participation in another interventional drug or medical device clinical trial within 28 days before screening.
* Positive test for SARS-CoV-2 at screening.
* Any other condition that, in the investigator's judgment, makes the participant unsuitable for participation in the study
