CD8A and infection: To be able to collect samples and perform analysis of both 1°M and 2°M CD8 T cells at the same time and this way minimize the variability between assays, we adopted the infection scheme depicted in the Figure 1A. Namely, 2°M CD8 T cell responses were generated in two steps: primary infection with H3N2 X31 followed 70 days later by secondary infection with H1N1 S12a.