XK and infection: Comprehensive study of the immune response generated by H5M2eN1-VLP vaccination revealed three layers of immune protective effects: (i) the production of neutralizing HA and NA antibodies against the cognate strain, although the HAI titer fell below the seroprotection level; (ii) a marked increase in the neutralizing avN1 antibody and cross-protection against the viral strains which are phylogenetically closely related to the NA of H5N1 such as CA/07; (iii) to recall the viral-specific anti-HA2 antibody against heterologous stains during early infection.