Seasonal Influenza Vaccination: Its Expected and Unexpected Effects

Vaccination can induce immune response to protect people against antigenically related virus strains. Although influenza is a vaccine preventable infectious disease, seasonal influenza epidemics still occur annually; and occasional but dramatic pandemics emerge. The reason lies in two evolutionary events regarding influenza viruses: antigenic drift and shift. They continuously generate new strains which annual seasonal and pandemic vaccination aims to track. Recently we proposed a mathematical model to examine the interaction between infection and vaccination. The results from our model showed that vaccination for seasonal influenza protects the vaccinated against vaccine strains (its expected effect), however, the effect of seasonal vaccination on the potential emergence of a future pandemic strain (unexpected effect) remains more uncertain. Further, the effectiveness of the proposed universal vaccines that are designed to provide full spectrum immune protection against seasonal and pandemic influenza will depend on their strength of cross-immunity relative to that induced by natural infection.