a more important clinical implication of this work is the identification of a universal neutralizing epitope in the ha stalk at the atomic level an important intellectual landmark for the development of a universal influenza vaccine. in the absence of the immunodominant head domain, isolated portions of the ha stalk that include the fi6 epitope and have already been shown to stimulate broad, but not universal, protective effects against h1n1 and h3n2 strains in vaccinated animals. using protein engineering and adjuvants to focus the immune system on the fi6 epitope may be the critical next step along the path to a universal vaccine.