"The hunt for a universal flu vaccine, a single shot that would provide lifelong immunity, has been going on for decades, and many teams of researchers have been on the case. The effort is complicated because there are some 16 types of key surface proteins (hemagglutinin) that help the virus bind to host cells, in addition to the several varieties of viral neuraminidase proteins. (These proteins are what the "H" and "N" stand for in viral designations such as H1N1.) Flu vaccines work by introducing a killed version of circulating virus strains, which trains the body's immune system to recognize and attack similar invaders in the future. Changes in the viruses' proteins help it evade identification by the immune system. A series of discoveries by different groups of researchers have zeroed in on a highly conserved (nonmutated) region of the virus. And a new study, published online October 18 in Proceedings of the National Academy of Sciences, has piggybacked on these findings to develop synthetic vaccine that has been effective in warding off several different types of influenza in mice. How does it work—and could it work in humans?" - Lit