CD4 and infection: However, the finding that primary NMI infection induced a comparable level of protection against the high dose NMI reinfection in WT and CD4+ T cell deficient mice was supported by our previous studies by demonstrating that the viable NMII vaccine (21) and the formalin-inactivated-NMI vaccine (29) also provided a similar level of protection in WT and CD4+ T cell deficient mice.