XK and influenza: While the role of NA-induced immune response is unquestionable, the levels of NA-specific antibodies are only modest in people immunized with the standard influenza vaccine containing 15 μg of the hemagglutinin of each strain; yet, an eight-fold increase in the levels of NA-specific antibody was detected when four times concentrated standard vaccines were used, suggesting an increased amount of the NA antigen in vaccine can ensure a better immune response to NA11.