The long-held approach to predicting seasonal influenza vaccine effectiveness may need to be revisited, new research suggests. Currently, seasonal flu vaccines are designed to induce high levels of protective antibodies against hemagglutinin (HA), a protein found on the surface of the influenza virus that enables the virus to enter a human cell and initiate infection. New research conducted by scientists at the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, found that higher levels of antibody against a different flu surface protein — neuraminidase (NA) — were the better predictor of protection against flu infection and its unpleasant side effects. Neuraminidase, which is not currently the main target antigen in traditional flu vaccines, enables newly formed flu viruses to exit the host cell and cause further viral replication in the body.