Multiple studies have documented NA stalk deletions in various influenza strains: A/Hong Kong/159/97 (H5N1) possesses a 19-aa deletion (positions 54–72) that reduces viral release capacity; A/chicken/Hubei/327/2004 (H5N1) contains a 20-aa deletion (positions 49–68); while A/Puerto Rico/8/34 (H1N1) and A/WSN/33 (H1N1) exhibit 15-aa (positions 63–77) and 16-aa (positions 57–72) deletions, respectively [10,11]. The gene discussed is XK; the disease is influenza.