XK and influenza: At present, several anti-influenza viral drugs have been approved by the FDA or other countries and can be divided into three categories according to their mechanisms of action, including inhibiting viral entry into host cells (HA inhibitor and M2 inhibitors), inhibiting viral replication (RdRp inhibitors), and inhibiting viral particle release from infected cells (NA inhibitors; Fig. 1, Tables 1 and 2) (131).