COmbination Therapy With Baloxavir and Oseltamivir 1 for Hospitalized Patients With Influenza (The COMBO Trial 1)

Up to 60 hospitalized patients with laboratory confirmed influenza who provide informed consent and meet trial inclusion/exclusion criteria. Experimental Design and Methods In a randomized, double-blind, placebo-controlled Phase 2-like, investigator-directed trial, hospitalized patients with laboratory confirmed influenza meeting inclusion and exclusion criteria, will be provided information on the trial, offered enrollment, and enrolled randomly in a 1:1 ratio to one of two groups upon signing of the study's informed consent form: Group 1, the combination treatment group (oseltamivir and baloxavir); Group 2, the standard treatment group (oseltamivir and placebo). * Group 1, the combination treatment group will receive oseltamivir and baloxavir * Oseltamivir: 75 mg po bid for 5 days * Baloxavir: 40 mg po once for wt \< 80 kg OR 80 mg po once for wt \>/= 80 kg * Group 2, the standard treatment group will receive oseltamivir and placebo * Oseltamivir: 75 mg po bid for 5 days * Placebo: Once Oseltamivir dosing may be reduced for patients with decreased renal function as follows, per treating physician: * CrCl \> 60 mL/minute: No dosage adjustment * CrCl \> 30 to 60 mL/minute: 30 mg po bid * CrCl \> 10 to 30 mL/minute: 30 mg po qd * HD: 30 mg po once and 30 mg po after each HD session * CAPD: 30 mg po once * CRRT: 30 mg po qd After assignment of a unique study number after signing informed consent, baseline data will be collected at time 0 including personal and clinical information and protocol directed laboratory specimens - nasal swabs for influenza PCR for patients who only had a rapid antigen test and blood specimens for patients who consent to additional blood drawing (for improved efficacy and safety analyses; not required for enrollment). Patients will be given oseltamivir by their healthcare providers. Research personnel's only involvement for oseltamivir dosing will be to remind providers that earlier treatment improves efficacy. Patients will then be given a single dose of baloxavir or placebo by the study's CRC as per a computerized random allocation scheme with dose determined by weight (as above); the CRC will notify the patient's provider that the patient has been given the single (blinded) dose. At time 1, 2, 3, 4, 7, and 30 days, nasal swabs will again be obtained, clinical information will be obtained from the patient via interview and review of the EMR, and blood specimens for patients who consented to additional blood drawing. Follow up will continue for 30 days. Efficacy and adjudicated safety data points will be assessed by a Data Monitoring Committee (DMC) quarterly and as needed throughout the trial.