France would have had hundreds of outbreaks of H5N1 bird flu on poultry farms in the past year had it not vaccinated ducks against the disease for the first time, according to a modelling study. Instead, there were just 10.
鈥淭he conclusion is that vaccination made a huge difference,鈥� says at the National Veterinary School of Toulouse, France.
While bird flu vaccines for poultry have long been used in some countries in Asia, many other nations haven鈥檛 adopted them. Besides the costs of vaccination, there are concerns that vaccinated birds could become infected without showing symptoms, allowing the disease to spread undetected.
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鈥淭here is a possibility that vaccination will be more widely used after this success in France,鈥� says at the Estonian University of Life Sciences in Tartu, who wasn鈥檛 involved in the study. 鈥淚t can be applied in a targeted way in high-risk areas and high-risk populations. Birds kept outdoors are one of the high-risk populations.鈥�
Since 2020, a particularly nasty form of H5N1 has been spreading worldwide among wild birds, and these birds can sometimes infect poultry on farms.
Many mammals exposed to dead or dying birds have been infected too, but the virus hasn鈥檛 been spreading from mammal to mammal 鈥� except among dairy cows in the US. These dairy cow outbreaks have resulted in a number of human infections.
Farm outbreaks have so far resulted in the death or culling of at least 130 million birds in 67 countries. In Europe, France has been especially hard hit, with nearly 400 outbreaks on farms in the 2022 to 2023 season.
One reason why is that large numbers of ducks are reared in France. Duck farms are more susceptible to becoming infected and also more likely to spread the disease, says Vergne. One reason for this is that ducks raised for foie gras are initially reared on one farm and then distributed to several others for fattening.
So in 2023, France decided to vaccinate all ducks, with the costs mostly covered by the government. While there were just 10 poultry farm outbreaks in the 2023 to 2024 season, there were also fewer outbreaks in the rest of Europe too.
To assess the effect of the vaccination campaign, Vergne and his colleagues looked for correlations between the number of reported cases in wild birds and the number of farm outbreaks in previous years.
鈥淥ur models predicted a much higher number of outbreaks if vaccination had not been implemented,鈥� says team member at the National Veterinary School of Toulouse. France will be continuing vaccination for another year, although the government has reduced the proportion of the costs it covers.
Farm outbreaks can spread to wild birds and vice versa, says Vergne. So he thinks it is possible that France鈥檚 vaccination campaign contributed to the reduction of farm outbreaks in other countries, including the UK.
鈥淭his may be true for certain regions in Europe which are connected with France by migratory routes of wild birds,鈥� says Viltrop. 鈥淏ut I think this remains a hypothesis and would be difficult to prove.鈥�
Whether vaccination will be tried by other countries in Europe depends on many factors, he says. 鈥淭he decision will be made weighing the risk, the cost and the benefits,鈥� says Viltrop. 鈥淚t depends on the risk of infection and if there is less virus circulating in wild birds, the need to vaccinate may not be so urgent.鈥�
While vaccination could help control disease outbreaks in the short term, in the longer term Vergne and Guinat both think farming practices need to be changed to reduce the risk of diseases spreading. 鈥淲e need to rethink, to make the system more robust,鈥� says Vergne.
For instance, one issue is that there are often lots of poultry farms in one area. 鈥淚f we imagine farms more distributed over space and less concentrated in some very precise locations, then we would expect the virus to spread at a lower rate and the veterinary services to be less overwhelmed when there is a surge of outbreaks,鈥� he says.
Birds could also be modified to make them less susceptible. A team in the UK has gene-edited chickens to make them resistant to bird flu, for instance. But it will take decades to roll out this technology, the researchers say.
bioRxiv
