To what extent may the duck population be protected after vaccination against highly pathogenic avian influenza?...

Faced with increasingly disastrous avian influenza crises, and considering the associated zoonotic risk, France launched a vaccination campaign against highly pathogenic avian influenza on duck farms with more than 250 ducks in October 2023. In the context of this paradigm shift in the fight against HPAI, our study was designed to (i) provide an overview of the vaccination campaign over the first six-month period and (ii) evaluate the level of assumed vaccine protection at population scale through a simple modelling approach - using actual duck population dynamics, data related to the recommended vaccination protocol, and biological data on vaccination-induced humoral responses obtained from experimental studies - and real-world data on how vaccination was actually implemented in the field between 1 October 2023 and 31 March 2024, corresponding to the level of compliance with the vaccination protocol. Vaccination compliance appeared satisfactory, with high vaccination coverage at flock level (more than 95% of duck flocks being vaccinated at least once during the studied period). Ages at vaccination and time between doses were in line with the vaccination protocol. Regarding the assessment of the level of assumed vaccine protection, both theoretical model and actual vaccination data indicated that, at any given time point, maximum 40-50% of duck batches were considered fully protected, through either the second dose or the booster, while 30-40% of the vaccinated flocks were either considered only partially protected (primary protection through the first dose) or their protection was seen to wane six weeks after the second dose. Our work can inform the testing and optimisation of vaccination strategies, and complementing our data-driven approach with serological monitoring, evaluation of vaccine efficacy, or spatio-temporal modelling of coverage across territorial scales would be pivotal to fully capture the interplay between vaccination, population dynamics, stakeholder decision-making, and epidemiological dynamics.