Among many types of influenza vaccines, live-attenuated influenza vaccine (LAIV) is one of the strongest inducers of CD8+ T cell response (Korenkov et al., 2018), and the S-FLU virus used in this study is similar to LAIV in terms of generating T cell mucosal immunity in mice and ferrets (Powell et al., 2012; Nogales et al., 2016). Here, CD8A is linked to influenza.