Co-occurring mutations of HA and NA occurred in some patients with different clinical characteristics, for example, patient with co-occurring mutations of HA-A158E, NA-I99V and NA-G298A in A(H1N1)pdm09 did not have influenza-related complications such as pneumonia, and fever cleared 3 days after treatment with standard dose of oseltamivir. This evidence concerns the gene XK and influenza.