We speculated that this phenomenon might be due to the fact that IL-2 and/or IFN-γ-secreting CD8+ TCM subsets at early times after vaccination result in the development of a larger pool of long-lived specific CD8+ TM cell subsets (e.g., CD8+ TCM, TEM and TEMRA subsets), which could lead to improved control against re-infection. This evidence concerns the gene IFNG and infection.