CD4 and influenza: The c-di-GMP adjuvanted virosomal H5N1 vaccine induced homologous (H5N1) and hetero-subtypic (pH1N1) influenza-specific CD4+ Th1 cells and significantly higher (p<0.01) frequencies of CD4+ Th1 cells were produced after mucosal (IN and SL) than IM administration (figure 8).