Seasonal influenza vaccines: evolutions and future trends.

Influenza vaccines are among the oldest still in active use. Purity, potency and standardization have been improved over the years. However, they are still produced using the same basic methods as when they were first introduced and evaluated by the US Armed Forces during and after the Second World War. For some time, the trivalent inactivated influenza vaccines have been recognized as having deficiencies. These deficiencies are now being addressed by a number of innovative approaches in vaccine development. These include strategies for broadening the vaccine-induced immune response, increasing the duration of protection, improving the protection induced in older individuals and reducing dependence on the egg supply. Each new vaccine will need to be evaluated carefully, ideally against placebo as well as against a standard vaccine, to determine absolute and relative efficacy. Such data will be necessary to inform decisions on making selections for use.