At both early (day 28) and late (day 60) memory time points, the numbers of NP-specific CD8+ T cells in the mLN of S-FLU–vaccinated mice were significantly lower (4.8-fold) than the numbers present in influenza virus–infected mice, and while a similar trend was observed in the lung, the number and composition (predominately effector memory, CD44+CD62L−) of NP-tetramer+ CD8+ T cells in the spleen of vaccinated mice matched those generated following natural infection (Fig. 1F). This evidence concerns the gene CD8A and infection.