A recent article surveyed immunity to N1 neuraminidase in a population in British Columbia, Canada^*.  Sera was obtained during August 2024 from 575 participants classified among ten age groups from one to 80 years of age.  Neuraminidase inhibition antibody titers were assessed by ELISA assay against H5N1 clade 2.3.4.4b.  In assessing N1 titers, 70 percent had detectable antibodies with half of the total yielding a low to moderate value, 32 percent at an intermediate threshold and 17 percent with a high concentration of antibody.  The level of antibody was consistent with previous exposure to H1N1 influenza pandemics in cohorts born from 1997 to 2003, many children exposed during the 2009 H1N1 outbreak and among those born before 1947.

The authors concluded that “a substantial proportion of the population has pre-existing anti-N1 against H5N1 with age-related variation”.

It is difficult to reconcile the low rate of infection attributed to H5N1 among workers with intensive exposure during depopulation and decontamination of infected poultry farms. A comprehensive epidemiologic survey of dairy and poultry workers has yet to be published.

It is generally conceded that workers at risk of exposure to H5N1 should be vaccinated against the prevailing seasonal influenza quadrivalent product to minimize the risk, albeit slight, of a recombinant event.  It is also suggested that dairy and poultry farm and processing workers should be vaccinated using an available H5N1 vaccine as deployed in Scandinavia for poultry and fur-farm workers.

^*Skowronski, D. M., Cross-Reactive H5N1 Neuraminidase Antibodies by Agent Influenza Imprinting Cohorts of the Past Century: Population-Based Sero Survey, British Columbia, Canada J. Infectious Diseases.  doi.org/10.1093/infdis/jiag 030 (2026)