As such, we compared the antibody profile to HA and NA in two naturally infected human cohorts in Auckland, New Zealand: (i) a serosurvey cohort, consisting of pre- and post-influenza season sera from PCR-confirmed influenza cases (n = 50), and (ii) an immunology cohort, consisting of paired sera collected after PCR-confirmation of infection (n = 94). This evidence concerns the gene XK and infection.