Annual influenza vaccination affects the development of heterosubtypic immunity

► Annual vaccination of all children against flu is recommended in some countries. ► In animal models, H3N2-vaccination prevents heterosubtypic immunity against H5N1. ► Reduction of this immunity correlated with the reduction of flu-specific CTLs. ► Unvaccinated children had more flu-specific CTLs than vaccinated children with CF. ► These findings highlight the importance of the development of universal flu vaccines.