XK and infection: To further dissect how viral gene expression patterns influence SIE, we individually gated all seven possible combinations of HA, NA, and NS1 expression by rPR8 (HA+ NA+ NS1+, HA+ NA+, HA+ NS1+, NA+ NS1+, HA+, NA+, NS1+) and directly compared their rH3N2 infection frequencies (the gating scheme is shown in Fig. S5A).