Cross-reactive H5N1 Neuraminidase Antibodies by Age and Influenza A Imprinting Cohorts of the Past Century: Population-Based Serosurvey, British Columbia, Canada

A substantial proportion of the population has pre-existing anti-N1 against H5N1, with age-related variation reflecting H1N1 imprinting and exposure opportunities. Through heightened attack rates and shifts in immunological hierarchies, historic pandemics shape and expand the immune repertoire with implications for pre-immunity to emerging zoonotic threats.