Influenza viruses are a significant public health threat, causing both annually circulating epidemics and unpredictable pandemics. Vaccination is the best means of control against individual cases of influenza and also for decreasing epidemic spread in the population. However, rapid influenza virus evolution requires continual reformulation of vaccines for annual influenza epidemics, and because pandemics cannot be accurately predicted, no current vaccine strategy can induce broad protection against all subtypes of influenza viruses. Recent work has suggested that such broadly protective, or "universal", influenza virus vaccines might be achievable using vaccine strategies that target conserved B- and T-cell epitopes.