#19,101
After years of increasing agricultural losses from avian influenza, many poultry farmers are understandably anxious for permission to protect their flocks with HPAI vaccines, yet most countries have been slow to embrace that strategy.
While we've seen some impressive success stories (see OFID: Avian H5, H7 & H9 Contamination Before & After China's Massive Poultry Vaccination Campaign), we've also seen some significant failures (see J. Virus Erad.: Ineffective Control Of LPAI H9N2 By Inactivated Poultry Vaccines - China), often due to poorly designed and/or applied vaccines.This hesitancy is based on mixed results seen in countries where AI vaccination has been adopted, and concerns over how vaccination might affect international trade.
The biggest concern is that a vaccine that is only partially effective may merely mask the symptoms of infection, but still allow the virus to spread stealthily and continue to evolve (producing vaccine-induced escape mutants).
Eleven months ago, in NPJ Vaccines: Impact of Inactivated Vaccine on Transmission and Evolution of H9N2 Avian Influenza Virus in Chickens, a report warned that inactivated vaccines have failed to prevent - or even reduce - H9N2 in China's poultry, and may have driven viral evolution (including mammalian adaptations).
Which is why most countries - including the United States, Canada and the UK - have yet to authorize HPAI poultry vaccines, although many are studying the matter (see UK Defra Announces New Avian Influenza Vaccine Trials Begin in UK).
France, however, was an early adopter in Europe, and in the summer of 2023 announced their intention to begin vaccinating high risk poultry (ducks) against H5N1 that fall, after testing showed a two-dose regimen provided adequate protection.
Within months, however - after several breakthrough infections - the French MOA Ordered 3rd Vaccine Dose For High Risk Ducks.
Last December, the Journal Vaccine carried a study which looked at the effectiveness of the French vaccination campaign.
To what extent may the duck population be protected after vaccination against highly pathogenic avian influenza? Contributions from a modelling approach and French field data
M. Salines a, M. Andraud a, A. Scoizec a, A. Schmitz b, E. Niqueux b, A. Jimenez Pellicer c, K. Bucher c, G. Gerbier c, N. Eterradossi d, B. Grasland b, S. Le Bouquin a
Earlier this month the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) published their own summary and analysis; reporting that less than half of the duck population was adequately protected at any given time.
Vaccinating ducks against avian influenza: lessons learned from the first six months
(Excerpt)
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.
While vaccination helped to reduce the burden of H5N1, it did not eliminate it. ANSES goes on to warn that:
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.
Last August, in Vaccine X: H5N1 Highly Pathogenic Avian Influenza Vaccination: Seroresponse of Mexican Poultry in the 2022–2024, we looked at the first two rounds of HPAI poultry vaccination in Mexico.
While seroconversion and seroprotection rates approached or exceeded 80% in many states, in the breakdown of the 20 states included in the first round, 7 (33%) scored considerably lower, with 2 states in single digits.
And that's the rub.These limitations were evident in period one, mainly across southeastern Mexican states because they did not mount an immune response after vaccination with seroconversion and seroprotection rates less than 10 % of their population.
It is likely that some of the critical points of the vaccination plan were not fully met or were not carried out properly.
Done right, and vaccination can be highly beneficial. Done wrong, and you could be conducting an unintentional Gain-of-Function field experiment.
We've discussed some of the ongoing biosecurity measures that would be required to mount a safe and effective poultry vaccination campaign (see UK Joint Taskforce Policy Paper: Vaccination of Birds Against HPAIV (bird flu), including:
- Most captive birds would likely require more than one vaccination over their lifetime, and regular testing that can differentiate infected from vaccinated animals (DIVA) would be needed to prevent `asymptomatic spread' of the virus.
- Culling and/or quarantine would still be needed for `breakthrough' infections
- A different vaccine, schedule and testing regimen would likely be required for non-avian livestock.
