Pre-pandemic and pandemic influenza vaccines.

Vaccination is considered the most effective strategy to control influenza and becomes particularly important when a new subtype or distantly related strain of virus enters the human population causing a world-wide epidemic or "pandemic". Depending upon the virulence of the emerging virus, a lack of pre-existing immunity can lead to overwhelming morbidity and deaths ranging in the millions. While the correlates of immunity to influenza are yet to be fully understood, our experience with vaccines over many decades enables pre-pandemic planning to develop strategies to minimise the impact of a human pandemic. This review explores developing pandemic and pre-pandemic vaccines in the context of highly virulent avian H5N1 virus and the influenza H1N1 pandemic of 2009.