Dose Ranging Study to Evaluate the Efficacy and Safety of MEDI8852 in Adults Who Are Hospitalized With Type A Influenza.

Inclusion Criteria: Age 18 years or older at the time of screening. Written informed consent and any locally required authorization (eg, Health Insurance Portability and Accountability Act \[HIPAA\] in the United States, Data Privacy Directive in Europe) obtained from the subject/legal representative prior to performing any protocol related procedures, including screening evaluations. Females of childbearing potential who are sexually active with a nonsterilized male partner must have evidence of not being pregnant upon enrollment and have a negative pregnancy test prior to administration of investigational product. Females of childbearing potential are defined as those who are not surgically sterile (ie, bilateral tubal ligation, bilateral oophorectomy, or complete hysterectomy), premenarchal, or postmenopausal (defined as 12 months with no menses without an alternative medical cause). Hospitalized ≤ 72 hours prior to receipt of a positive diagnostic test for influenza A; confirmed with positive rapid antigen test (supplied or approved by the sponsor), or confirmed with culture, polymerase chain reaction, or antigen testing at the study site. Onset of influenza symptoms ≤ 144 hours (≤ 6 days) prior to randomization. Receiving supplemental oxygen. Expected to participate in the study through Day 60. Exclusion Criteria: * Any condition that, in the opinion of the investigator, would interfere with evaluation of study drugs or interpretation of subject safety or study results. * Concurrent enrollment in another clinical study involving an investigational treatment. -Hospitalized \> 72 hours (\> 3 days) prior to receipt of a positive diagnostic test for influenza A. * Receipt of \> 72 hours or \> 6 doses of treatment with a neuraminidase (NA) inhibitor. -Receipt of any investigational antiviral medications within 30 days prior to study drug dosing. * Previous receipt of an influenza mAb within past 100 days. * Pregnant or nursing female. * History of allergic disease or reactions likely to be exacerbated by any components of the study drugs (MEDI8852 or oseltamivir). * Diagnosis of influenza B infection within 14 days prior to randomization. * Employees of the sponsor, clinical study site, or any other individuals involved with the conduct of the study, or immediate family members of such individuals.