CD8A and viral infectious disease: Many reports have shown that viral-specific cytotoxic CD8+ T cells, induced by not only virus infection but also vaccines, provide cross-protection, although a high dose of antigen and optimal adjuvants are apparently needed to elicit viral-specific cytotoxic CD8+ T cells in influenza vaccines (Budimir et al., 2012; Furuya et al., 2010; Guo et al., 2011; Laidlaw et al., 2013).