A series of nanoparticle-based vaccines elicits protective antibodies against various strains of the influenza virus in nonhuman primates, according to work from Nicole Darricarrère and colleagues. Although more research is needed, the vaccines mark an important step toward a universal flu vaccine for humans, which has long been a major goal for infectious disease researchers. Current seasonal flu vaccines can prevent disease but often only work for a year, after which a new vaccine must be developed. This occurs because influenza viruses evolve extremely quickly, meaning that a year-old vaccine may not prepare the immune system to recognize a new strain. A universal vaccine that could remain effective year-to-year would represent a major medical accomplishment but creating such a vaccine has been challenging. However, scientists theorize that a universal vaccine might work if it incorporated key proteins on the surface of the influenza virus that remain constant during evolution, such as those that allow the virus to enter cells. Based on this strategy, Darricarrère et al. tested influenza vaccines that use nanoparticles to deliver modified forms of hemagglutinin (HA) influenza virus surface proteins and an emulsion vaccine adjuvant. When given to nonhuman primates, the vaccines stimulated the production of protective antibodies against multiple H1 and H3 influenza A viruses - the ones most likely to cause pandemics. Furthermore, the antibodies were potent and recognized viruses in a similar way as human antibodies, suggesting the vaccines might provide broad immunity. Darricarrère et al. note that although their study didn't evaluate the durability of vaccine responses, their vaccines are also currently being tested in early clinical trials.