Several lines of experimental evidence suggest that H1N1 infections accompanied by a characteristic impairment of the innate immune response. By monitoring the host functional response, patients with increased risks of developing severe influenza-associated complications could be identified immediately [11, 12] . The preliminary data from this study showed that the frequency of CD19 + B cells in patients with severe H1N1 was significantly higher than in the moderate and control groups (Figure 1e) , and the frequency of NK cells in the severe and moderate groups were less than that of the control group. In the host innate immune system, NK cells are the major effector cells during acute infection, rapidly killing infected cells in the process. Previous studies have shown that the significant decrease in peripheral NK cell count is mainly because the S-OVI directly infected and killed NK cells, thereby limiting their activity and leading to their apoptosis in vivo [13] .