CD8A and infection: There are indications [10–13] that prior infection with seasonal IAVs in humans can generate a measure of cross-reactive, or “heterosubtypic”, CD8+ cytotoxic T lymphocyte (CTL)-mediated immunity against further infection with other, serologically distinct seasonal or pandemic IAVs but, because of the limited case numbers to date, our understanding of how that plays out for H7N9 infection is rudimentary.