Evaluating the Safety and Efficacy of Anti-Influenza Intravenous Hyperimmune Immunoglobulin (IVIG) in Adults Hospitalized With Influenza

Inclusion Criteria: * Signed informed consent * Locally determined positive influenza test (by polymerase chain reaction \[PCR\] or other nucleic acid test, or by rapid antigen \[Ag\]) from a specimen obtained within 2 days prior to randomization * Onset of illness no more than 7 days before randomization, defined as when the participant first experienced at least one respiratory symptom or fever * Hospitalized (or in observation unit) for influenza, with anticipated hospitalization for more than 24 hours. Criteria for hospitalization will be up to the individual treating clinician. * For women of child-bearing potential: willingness to abstain from sexual intercourse or use at least one form of hormonal or barrier contraception through Day 28 of the study * Willingness to have blood and respiratory samples obtained and stored * NEW score greater than or equal to 2 at screening (see the protocol for more information on this criterion) Exclusion Criteria: * Women who are pregnant or breast-feeding * Strong clinical evidence (in the judgment of the site investigator) that the etiology of illness is primarily bacterial in origin * Prior treatment with any investigational drug therapy within 30 days prior to screening * History of allergic reaction to blood or plasma products (as judged by the site investigator) * Known immunoglobulin A (IgA) deficiency * A pre-existing condition or use of a medication that, in the opinion of the site investigator, may place the participant at a substantially increased risk of thrombosis (e.g., cryoglobulinemia, severe refractory hypertriglyceridemia, or clinically significant monoclonal gammopathy) * Presence of any pre-existing illness that, in the opinion of the site investigator, would place the participant at an unreasonably increased risk through participation in this study * Participants who, in the judgment of the site investigator, will be unlikely to comply with the requirements of this protocol * Medical conditions for which receipt of a 500 mL volume of intravenous fluid may be dangerous to the participant (e.g., decompensated congestive heart failure) * Receiving extracorporeal membrane oxygenation (ECMO) * Suspicion that infection is due to an influenza strain or subtype other than A(H1N1)pdm09, H3N2, or influenza B (e.g., H5N1, H7N9)