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Vaccine effectiveness (VE) of seasonal immunization against influenza illness necessitating medical attention has ranged from 19% to 60% (with lower VEs driven by mismatches between circulating viruses and vaccine strains). Unlike the variable hemagglutinin head (on which basis the vaccines are manufactured), the viral protein stem region is conserved; moreover, anti-stem antibodies are protective in animal models. To test the safety and efficacy of the anti-stem (influenza A) monoclonal antibody VIR-2482, investigators randomized 2977 unvaccinated participants (mean age, 39) at low risk for influenza complications to receive VIR-2482 (450 mg or 1200 mg) or placebo intramuscularly. The primary outcome was PCR-positive influenza-like illness…