Immune molecules known as antibodies that protect against influenza virus infection target the highly variable influenza protein HA. It is thought the antibodies generated by an individual's immune system protect against only a few closely related influenza viruses. However, new research indicates that some individuals vaccinated with seasonal influenza vaccine produce antibodies that can target the forms of HA used by the deadly H5N1 avian influenza virus and the recent swine-origin pandemic H1N1 influenza virus.