Here it is proposed that a genetically determined CD8+ T-cell deficiency does not lead to impaired control of EBV when primary infection occurs in early childhood, unless the deficiency is severe, but that when primary infection occurs in adolescence or adulthood after the normal age-related precipitous decline in CD8+ T cells the same genetic CD8+ T-cell deficiency is more likely to impair control of EBV infection. Here, CD8A is linked to Epstein-Barr virus infection.