Surveillance Strategy in Duck Flocks Vaccinated against Highly Pathogenic Avian Influenza Virus

Since 2016, epizootics of highly pathogenic avian influenza (HPAI) virus have threatened the poultry sector in Europe. Because conventional prevention and control measures alone were insufficient in some contexts, the European Commission authorized poultry vaccination in 2023. Subsequently, France launched a nationwide duck vaccination campaign combined with a comprehensive surveillance plan. We used a mathematical model to simulate the transmission of HPAI viruses in vaccinated duck flocks and assess the effectiveness of a wide range of surveillance strategies. Sampling and testing dead ducks every week (enhanced passive surveillance) was the most sensitive (approximate to 90%) and the most timely strategy. Active surveillance through monthly testing of a crosssectional sample of live ducks was the least sensitive and timely strategy. Thus, we advise focusing HPAI surveillance efforts on enhanced passive surveillance and reducing active surveillance of live ducks.