Vaccinating ducks against avian influenza: lessons learned from the first six months

In the November 2025 edition of the journal Vaccine, scientists from ANSES's Ploufragan-Plouzané-Niort Laboratory and the DGAL published an analysis of the first six months of the vaccination campaign on duck farms in France, covering the period from October 2023 to March 2024. They combined three different approaches: an analysis of the field data collected by the DGAL, a review of the results of experimental vaccine trials conducted in 2022, and modelling of the antiviral protection provided by the vaccine at population level.

One of the scientists’ objectives was to verify the level of protection achieved in the field. This is because “vaccination doesn’t prevent infection with the virus but limits the clinical signs and reduces viral shedding by infected animals, slowing its spread within and between farms”, affirms Béatrice Grasland, head of the Unit for Virology, Immunology and Parasitology in Poultry and Rabbits at ANSES.

Good overall compliance with the vaccination protocol

The main takeaway of the analysis was that the vaccination protocol was widely implemented over the period in question. Between 1 October 2023 and 31 March 2024, 51 million doses were administered, covering over 95% of duck flocks. Most of them received two doses – the first when the animals were around 10 days old and the second approximately 20 days later – in accordance with the vaccination protocol in force at the time. 

The data collected were fed into a model assessing how well the ducks were protected against avian influenza. “The model showed that 40 to 45% of the duck population could be considered protected by a complete vaccination scheme at a given time, which means they’d received all the doses required for optimum vaccine efficacy and that this efficacy hadn’t yet declined”, explains Morgane Salines, a scientist in ANSES's Epidemiology, Health and Welfare (EPISABE) unit and the main author of the study.

The rest of the duck flocks only had partial protection, either because their vaccination protocol was in progress or because their immunity was declining. Indeed, experimental estimates indicated that vaccine protection declined in ducks over the age of 10 weeks. “These percentages of fully or partially protected farms can ensure a certain level of protection for the duck population as a whole. Proper vaccination compliance by production sectors is essential to optimise this protection”, adds Salines. 

Various modelled scenarios

To offset the decrease in protection observed for ducks over the age of 10 weeks, a third dose was administered to ducks intended for foie gras production – which are kept for longer (up to 16 weeks) than broiler ducks – exclusively in particularly high-risk areas and periods. “Our modelling confirmed the benefits of this third dose”, states Mathieu Andraud, a scientist from the EPISABE unit who[MA1]  built the model. “Without it, the duck population in these areas would have been far less protected”. 

The model was also used to prospectively test several vaccination scenarios that have not yet been implemented. For example, in light of the cost of vaccination for the French government and production sectors, one possibility was to not vaccinate ducks all year round but rather to suspend vaccination during those periods when the risk of avian influenza transmission is the lowest. However, the modelling results showed that this would not be a good health strategy: “If we don’t vaccinate animals in summer, the time required to complete the vaccination protocol and for immunity to develop would leave ducks unprotected in autumn or winter, when the risk of avian influenza is very high”, explains Andraud. 

The vaccination strategy will continue to be optimised to better protect poultry farms. These developments are supported by modelling, which allows their impact to be estimated before they are rolled out in real-life conditions. For example, this has been the case with the vaccination of newly hatched ducklings, which has been gradually introduced since 2024. Vaccination protocols are also currently being studied with the aim of improving the protection of ducks over the age of 10 weeks.

Even with good vaccination results, control and surveillance efforts must be maintained

In the winters of 2023-2024 and 2024-2025, the number of avian influenza cases on farms fell sharply compared with previous years. This decrease can be attributed both to vaccination and to the reduced circulation of the virus in wild birds. 

“Currently, avian influenza is circulating more actively in wild birds than in the winter of 2024-2025”, underlines Grasland. “More than 40 instances of the virus being introduced into French farms from wild birds have been recorded since the start of the 2025-2026 season. In addition to vaccinating ducks, it’s important to continue implementing biosecurity measures – which prevent the virus from entering farms – and monitoring the virus, to prevent it from circulating at a low level. The goal is to ensure that the virus doesn’t develop mutations that could ultimately allow it to evade vaccination-induced immunity”. 

As a reminder, avian influenza can, under certain conditions, be transmitted to humans. Reassortment between an avian influenza virus and a human influenza virus could potentially result in a virus that spreads more easily to people. To reduce this risk of co-infection with both types of viruses, the French National Authority for Health issues a recommendation each year, advising professionals in contact with birds to receive the seasonal influenza vaccine.