The study will be conducted in two parts:~Part 1:~In Part 1, eight healthy subjects, 18 to 65 years of age, will be enrolled at one study center in the United States of America (USA) and will receive a single intravenous (IV) dose of MEDI8852 (Cohort 1, dose 1) on Day 1. The subjects will be admitted to a Phase 1 unit (Day -1), for dosing (Day 1) and for follow-up (through discharge from the Phase 1 unit on Day 2). Subjects will then be followed through Day 60 for treatment emergent adverse events (TEAEs), treatment emergent serious adverse events (TESAEs), treatment emergent adverse events of special interest (TEAESI), concomitant medications, nasal and blood PK, and ADA. Initiation of Part 2 of the study will be based on review of safety data from Part 1 (Days 1-8) by a study-specific Dose Evaluation Committee (DEC). For subjects in Part 1, the study is approximately 90 days in duration, consisting of a screening period of up to 30 days, a treatment period of 1 day and a follow-up period of 59 days.~Part 2:~In Part 2, approximately 60 healthy, influenza serosusceptible subjects, 18 to 65 years of age, will be enrolled at the same study center in the USA and will receive a wild-type A/H1N1 challenge strain on Day 1. Subjects will be randomized 1:1:1:1:1 into 5 cohorts (approximately 12 subjects per cohort) to receive the following on Day 2:~Cohort 2: A single IV dose of placebo~Cohort 3: OS, 75 mg orally BID (twice a day) for 5 days~Cohort 4: A single IV low dose of MEDI8852 (dose 2)~Cohort 5: A single IV high dose of MEDI8852 (dose 1)~Cohort 6: A single IV low dose of MEDI8852 (dose 2) and oseltamivir (OS), 75 mg orally BID for 5 days~The subjects will be admitted to the Phase 1 unit (Day -1), for influenza challenge strain administration (Day 1), dosing (Day 2 [Cohorts 2, 4 and 5] and Days 2-6 [Cohorts 3 and 6]), and follow-up (through discharge from the Phase 1 unit on Day 9). Subjects will then be followed through Day 14 for solicited influenza symptoms, and through Day 60 for TEAEs, TESAEs, TEAESIs, concomitant medications, nasal and blood pharmacokinetics (PK), and antidrug antibody (ADA). For subjects in Part 2, the study is approximately 120 days in duration, consisting of a screening period of up to 60 days, a treatment period of 8 days and a follow-up period of 52 days
The purpose of the study is to evaluate the efficacy and safety of MEDI8852 for the treatment of influenza caused by a wild type A/H1N1 challenge strain in healthy, influenza serosusceptible adults.