Annual influenza epidemics are associated with serious excess morbidity and mortality, particularly among the elderly. Licensed trivalent inactivated influenza vaccines (TIVs) have been shown to reduce hospitalization and death following influenza in this vulnerable population, but their efficacy is lower than that observed in younger, healthy populations. In addition, recent studies have questioned the level of effectiveness of TIV in the elderly, suggesting that cohort studies have overestimated the benefits of immunization with current TIV formulations in this age group. In view of these considerations, it is widely accepted that improved and alternative vaccines are needed for control of seasonal and pandemic influenza.