Our results revealed that the percentage of the IAV-specific IFN-γ positive CD4+ T cells was higher in the IAV single infection group (0.95 ± 0.1%) compared to that of IAV + SARS-CoV-2 (0.71 ± 0.01%, P = 0.018) and SARS-CoV-2 + IAV (0.35 ± 0.06, P < 0.0001) coinfection groups (Fig. 5G). Here, CD4 is linked to infection.