This study aims to evaluate the efficacy of antiviral prophylaxis in preventing in-hospital influenza transmission. We will enroll hospitalized patients with confirmed influenza (index cases) and their uninfected roommates (room contacts). These room contacts will be randomized in a 1:1:1 ratio to one of three prophylactic groups: placebo, suraxavir marboxil, or oseltamivir. The primary outcome will be the rate of influenza infection among the room contacts, which will be monitored to determine the effectiveness of the interventions.

1.Inclusion Criteria:

(1)Inclusion Criteria for Index Cases:

① Patients hospitalized at a participating medical institution.

• The subject and/or their legal guardian agrees to participate in this clinical study, has signed the informed consent form, and is able to comply with the protocol requirements for follow-up and complete all study procedures and assessments.

  • Age ≥ 2 years.

    • Positive for influenza virus as determined by a Rapid Antigen Test (RAT) or Nucleic Acid Amplification Test (NAAT) on a respiratory specimen (e.g., oropharyngeal swab, nasopharyngeal swab, sputum, or bronchoalveolar lavage fluid).

      (2) Inclusion Criteria for Room Contacts:

      ① Patients hospitalized at a participating medical institution.

• The subject and/or their legal guardian agrees to participate in this clinical study, has signed the informed consent form, and is able to comply with the protocol requirements for follow-up and complete all study procedures and assessments.

  ③ Age ≥ 12 years.

  • Expected to remain hospitalized for ≥ 72 hours.

    • Shares a room with at least one hospitalized index case who has been confirmed with influenza virus infection by RAT or NAAT on a respiratory specimen within the last 120 hours and developed influenza-related symptoms within the last 120 hours, and is expected to share the same room for ≥ 24 hours.

      ⑥ Negative for influenza virus as determined by a Nucleic Acid Amplification Test (NAAT) on a throat swab collected on Day 1.

      3.Exclusion Criteria

      (1) Index Cases There are no exclusion criteria for index cases. (2) Exclusion Criteria for Room Contacts:

      • Room contacts with a known allergy to the active ingredients or excipients of the investigational drugs.

• Room contacts who have been diagnosed with or have had an influenza virus infection in the past 12 weeks.

  • Use of any anti-influenza antiviral drugs within 2 weeks prior to screening, including: neuraminidase inhibitors, polymerase inhibitors, hemagglutinin inhibitors, and M2 ion channel blockers (e.g., Oseltamivir, Zanamivir, Peramivir, Favipiravir, Arbidol, Baloxavir Marboxil, Amantadine, or Rimantadine, or other anti-influenza drugs approved by the NMPA).

    • Known to be pregnant or breastfeeding. (Subjects who suspect they may be pregnant must report this to the investigator, who will confirm with a pregnancy test).

      • History of fever (axillary temperature ≥ 37.3°C) within 72 hours prior to screening.

        • Child-Pugh class B or C, or an eGFR ≤ 60 mL·min-¹·(1.73 m²)-¹. ⑦ Any subject deemed unsuitable for participation in the study by the investigator.