BACKGROUND
The ongoing panzootic of highly pathogenic avian influenza A(H5N1) presents a risk to human health both from infections resulting from exposure to infected birds or mammals, and from potential mutations enabling human-to-human transmission of a virus to which there is little or no population immunity.

AIM
This cohort study was designed with the aim of informing assessments of the risk of avian influenza to human health and the public health management of influenza A(H5N1) exposures.

METHODS
We recruited 428 individuals at 34 highly pathogenic avian influenza A(H5N1) outbreak sites between April 2023 to March 2025, throughout England. Through nasopharyngeal samples and questionnaires, we investigated risk factors including exposure periods and usage of personal protective equipment (PPE), and characteristics of influenza A(H5N1) infection.

RESULTS
The median participant age was 37 years (interquartile range: 28–51 years), 296 (69%) were male. Most participants (85%) reported full PPE use when exposed, and 82 (19%) were vaccinated against seasonal influenza. Six persons tested PCR-positive for influenza A(H5N1), of whom three (
CONCLUSION
We recommend continued conscientious PPE use and the resumption of enhanced surveillance following detection of an increased risk of animal-human transmission, with a One Health focus, to mitigate pandemic risk of influenza A(H5N1).