Seasonal influenza and vaccine herd effect

The seasonal influenza vaccine programs in many regions aimed to protect most vulnerable population, but current trivalent influenza vaccine does not provide sufficient effectiveness among people under high risk for severe outcome of the influenza. The vaccine herd effect (VHE) is the extra protection of non-immune high risk persons, with increase of immunity among vaccinated healthier persons which prevents circulation of influenza in the community. Accumulating evidences are supporting the immunization of extended population with regard to the VHE.