Professor, Veterinary Doctor, former Director of the National Veterinary School of Nantes (Oniris) and President of the Research Training Commission of the French Veterinary Academy, Pierre Saï co-signed in 2021 a report to the Minister of Agriculture and Food on the place of vaccination in the fight against highly pathogenic avian influenza. Even though, following the recommendations of this report, our country is going to experiment with two candidate vaccines for waterfowl in the Gers and the Landes, this specialist explains to us the challenges of these tests.
L’Express: The current episode of avian flu is particularly painful for farmers who have had to eliminate 12 million poultry. Following the example of France, several European countries are embarking on the experimentation of vaccines. Is this THE solution to solve the problem?
Pierre Sai: On a health level, the vaccine can become an essential option to prevent crises, but under certain conditions and in addition to the usual biosecurity measures. [mesures préventives et de sécurité, NDLR.]. So far, Europe was not in favor of it, in particular because vaccination risks masking an infection and harming exports. However, the tide is turning because the H5N8 virus frequently returns to several European countries, introduced by wild migratory birds from Asia where this virus seems to have taken hold (enzootics).
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In France, we had thought that it would only strike occasionally and that the barrier measures put in place on farms and early slaughter could be enough to stop viral circulation. Unfortunately, it is likely that the epidemic will return very frequently, even every year. Moreover, this year, the slaughters were much more massive than usual. We are therefore reaching the limits of the current French policy in the fight against avian flu. The purpose of the report submitted to the Ministry of Agriculture last year was precisely to specify the possible vaccination strategies for France. It is interesting to note that our country has been a driving force on this subject in Europe. If vaccine approaches are advancing today also among our neighbours, it is because the French government has taken up the subject and is bringing it to Community level during the French presidency of the Union.
What could France’s future vaccine strategy look like? Will it be a question of injecting preventive doses into millions of animals each year?
The recommendations contained in the report were submitted to the ministry in 2021. At the time, previous crisis episodes only concerned waterfowl in the Southwest. There had not yet been a massive epidemic among gallinaceans, in the Vendée for example. We had therefore recommended preventive vaccination only of waterfowl breeding areas at risk in the South West. This remains true, but there is not yet a vaccine available and authorized for waterfowl. But, recent news changes the situation because more than 10 million gallinaceans – for which vaccines are more advanced without them being authorized yet – have been slaughtered in the west of France. It will therefore probably be necessary to have a specific vaccine for each of these two species.
To develop preventive vaccination, an early warning and detection system is essential. It already exists since the International Office of Epizootics (OIE) lists dead wild birds carrying the virus from Northern Europe or Russia, before their congeners fly over France following the migratory corridors. This information, reinforced by that provided by the French State services (Anses in particular), must be used to trigger vaccination.
Will it be necessary to achieve collective immunity in farms, as for Covid in humans?
Absolutely. We already know that vaccines will not completely suppress viral circulation even if they greatly decrease it. In addition to the protective effect of vaccine candidates and the monitoring of their immunity, this question of herd immunity will also be studied in the vaccination field trials which start this month. Experimentation will also tell which route of administration should be chosen for vaccination.
Many countries refuse to import vaccinated poultry. Why so much reluctance?
From the moment we vaccinate, it is difficult to distinguish between vaccinated animals and affected animals. Hence this reluctance, including in Europe. However, immunological tests, which will be refined during the field trials which are beginning, do however make it possible to distinguish vaccinated animals from affected animals.
However, the reluctance in principle is in the process of being lifted, in particular at the initiative of France which has just taken over the presidency of the Union. It is likely that Europe will end up authorizing vaccination with a number of precautions on reassuring immunological monitoring for export. In addition, this vaccination will only be implemented in addition to maintaining the current barrier measures.
Why does the effectiveness of current barrier measures seem limited?
The structure of farms in France and in particular in the South-West poses a series of problems that the report submitted to the Minister has raised. Thus, the extreme fragmentation of farms into separate units according to the age of the animals leads, for example, to a multitude of movements of animals and people between farms and their units, which facilitates the spread of epidemic. When migratory birds carrying the virus fly over the Chalosse, they produce excretions which are ingested or inhaled by livestock. These then mix with healthy specimens during the various transports. The vehicles used for these transports are propagation factors. In addition, humans can also promote the circulation of the virus, for example by carrying it through their shoes or their equipment. Current protocols aim to reduce these risks. But they are no longer enough.
When might the vaccine be available?
It takes time. The State and the regions, co-financiers on an equal basis, as well as the foie gras interprofession (CIFOG) and the pharmaceutical laboratories potentially involved (CEVA and Boehringer-Ingelheim) have just signed an agreement on April 15 which provides for the start of preliminary field tests at the beginning of May. It takes 8 to 9 months before collecting complete results, thanks in particular to the participation of ANSES and the Toulouse Veterinary School. In the best case, a vaccine would therefore only be operational for the winter of 2023/2024. It will then be up to the Ministry of Agriculture to take – or not – the decision to use it.
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Another thing is certain: vaccination must be accompanied by a far-reaching diplomatic strategy aimed at importing countries, making it possible to protect French exports of ducks, chickens, as well as French strains with high added genetic value. In total, these exports represent approximately 250 million euros; an amount that greatly exceeds the foreseeable cost of vaccination against avian flu for the State.
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