Novel pathogenic strains of the influenza virus have also emerged with antigenically different HA and/or NA and have caused three pandemics in the 20th century: the Spanish influenza (H1N1) in 1918, responsible for approximately 50 million deaths; the Asian influenza (H2N2) in 1957 during which about 2–4 million people died; and the Hong Kong influenza (H3N2) in 1968 responsible for 1–2 million deaths [6]. Here, XK is linked to influenza.