The burden of influenza in older adults: meeting the challenge.

Influenza is an acute respiratory infection for which vaccination is our best prevention strategy. Small seasonal changes in circulating influenza viruses (antigenic drift) result in the need for annual influenza vaccination, in which the vaccine formulation is updated to better match the predominant circulating influenza viruses that have undergone important antigenic changes. Although the burden of influenza infection and its complications is the highest in older adults, vaccine effectiveness is the lowest in this vulnerable population. This is largely due to waning of the immune response with age known as "immune senescence", and presents an important, unmet challenge. Possible strategies to tackle this include adjuvant and high-dose vaccines, and herd immunity induced by greater vaccine uptake.