A Phase 2 randomized, double-blind, placebo-controlled trial of the monoclonal antibody MHAA4549A in patients with acute uncomplicated influenza A infection

Background MHAA4549A, a human monoclonal antibody targeting the influenza A hemagglutinin stalk, neutralizes influenza A virus in animal and human volunteer challenge studies. We investigated MHAA4549A safety and tolerability, efficacy, and pharmacokinetics in outpatients with acute, uncomplicated influenza A infection. Methods This was a Phase 2, randomized, double-blind, placebo-controlled trial of single intravenous (IV) doses of 3600 mg or 8400 mg MHAA4549A, or IV placebo in adult outpatients testing positive for influenza A. Patients were enrolled across 35 sites in 6 countries. Randomization and dosing occurred ≤ 72 hours of symptom onset; study duration was 14 weeks. The primary endpoint was the nature and frequency of adverse events (AEs). Secondary endpoints included median time to alleviation of all influenza symptoms, effects on nasopharyngeal viral load and duration of viral shedding, and MHAA4549A serum pharmacokinetics. Results Of 125 randomized patients, 124 received study treatment, with 99 confirmed positive for influenza A by central testing. Frequency of AEs between MHAA4549A and placebo groups was similar; nausea was most common (8 patients; 6.5%). MHAA4549A serum exposure was confirmed in all MHAA4549A-treated patients and was dose proportional. No hospitalizations or deaths occurred. Between MHAA4549A and placebo groups, no statistically significant differences occurred in median time to alleviation of all symptoms, nasopharyngeal viral load, or duration of viral shedding. Conclusions While MHAA4549A was safe and well-tolerated with confirmed exposure, the antibody did not improve clinical outcomes in patients with acute uncomplicated influenza A infection.