Chickens have still not received a flu shot.  A virologist wants to hurry

Bird flu is not high enough on the political agenda in the Netherlands. This is the conclusion of Thijs Kuiken, virologist and professor at Erasmus MC in Rotterdam and a member of Dutch and European working groups that advise on the approach to bird flu. “Vaccinating poultry against the flu is now a priority,” says Kuiken, “to prevent even more culling and because of health risks for humans.”

The current outbreak of avian flu in Europe is the largest ever, reported the European infectious disease service ECDC in October. Since this epidemic began in October 2021, around 2,500 outbreaks have been reported in Europe on poultry farms and over 3,500 outbreaks among wild birds, from Spitsbergen to southern Portugal and Ukraine. About 50 million chickens and other poultry have been culled, including 5 million in the Netherlands. Last month, the Dutch counter almost reached 900,000, of which 300,000 on one company.

Do not trade prohibited

The Dutch Poultry Farmers’ Union is also in favor of vaccination, said chairman Bart-Jan Oplaat in this newspaper earlier this year. But under conditions: there must be no trade barriers and the vaccine must be really good. It should not only prevent infection and disease, but also virus transmission: otherwise it can spread unnoticed.

“If you the European rules if you read it carefully, you will see that there are in fact no trade barriers,” says Kuiken. “Preventive vaccination is allowed, also as a long-term strategy. Countries can decide for themselves.” In other words, there is no law that prohibits the trade in vaccinated poultry, he emphasizes. “Only: everyone thinks that is the case. And that’s why farmers don’t want to touch it.”

The Ministry of LNV is aware of this, the spokesperson responds, and Europe is working hard on a solution. A draft regulation for 2023 ‘indeed states that trade in meat from vaccinated animals is allowed, provided that animals can be shown to be free of infection. Monitoring rules are now being drawn up for this.”

In the Netherlands, only a vaccine based on a low-pathogenic strain is currently registered

However, the practice is unruly, as the ministry also sees: “The EU rules therefore do not stand in the way of vaccination, but they do impose additional conditions on the trade. And that can entail costs for market parties. In practice, companies in the EU or elsewhere can refuse products from vaccinated animals. She is free to do that.”

Vaccinating in advance with existing vaccines is not a good idea, says Mart de Jong, professor of quantitative veterinary epidemiology at Wageningen University & Research, who conducts research into bird flu vaccines. In the Netherlands, only a vaccine is registered that is based on a so-called low-pathogenic strain from 1986, he says. “That does not work well against the current highly pathogenic avian flu.”

Read also: Bird flu is always around. Why are virologists holding their breath now?

So why aren’t pharmaceutical companies working hard on better vaccines? De Jong sees a chicken-egg problem. “European countries only want to trade among themselves in non-vaccinated poultry,” he says, “because it is difficult to distinguish vaccinated animals from sick animals.” Since there is therefore no international market for vaccinated animals, poultry farmers do not want to vaccinate their animals – and pharmaceutical companies are reluctant to invest in better vaccines.

In any case, manufacturers should be constantly adapting their vaccines to the prevailing avian flu variant, just as is currently done with human flu vaccines. But there is something else going on, De Jong emphasises. “Many of the current vaccines work well in the lab, but their effectiveness in the field is disappointing,” he says. “This is especially true for the traditional vaccines, which consist of an inactivated virus. We see much lower amounts of antibodies in the field. The question is whether this is also the case with newer types of vaccines. We are now looking into that.”

Broader immune response

If the amount of antibodies is too low, a vaccine will not protect well against virus transmission. Vaccinated animals can then still pass on the virus to each other. “Then you lose control of the spread,” says De Jong. “And then people can be exposed to the virus unnoticed.”

Experts hope this is different with the latest generation of vaccines. They are more complex – just like the corona vaccines, for example – and ensure a broader and longer-lasting immune response. De Jong: “But whether, and if so how, this helps to protect birds against virus transmission at low levels of antibodies, is not yet clear.”

At the end of 2021, the ministry released money for research into better vaccines. That is now happening in Wageningen. “We are investigating, among other things, how you can better stimulate immunity with newer types of vaccines and how you can prevent transmission in practice.”

In any case, newer vaccines do make it possible to distinguish between sick and vaccinated animals. These vaccines no longer consist of a complete, inactivated virus, but are based on a specific surface protein of the relevant virus: a hemagglutinin protein in the case of the avian flu virus, and the spike protein in the case of the coronavirus. The immune system will therefore only make antibodies against them; you can see that in a blood test.

Silent circulation

Professor Thijs Kuiken, meanwhile, urges greater urgency. “In an emergency situation you have to take emergency measures,” he says, “and in this case vaccinate as soon as possible. As far as I am concerned, that should have been possible immediately after 2003.” Then an outbreak of a highly pathogenic variant arose in Dutch poultry farming. More than 30 million birds were culled and a veterinarian died of the virus.

The argument that the existing vaccines provide insufficient protection against transmission of the virus does not carry enough weight in Kuiken’s opinion. “Such a vaccine in any case limits the amount of virus in circulation,” he says, “and thus also the risk of further outbreaks and dangerous mutations of the virus. And we know from the literature that ‘silent circulation’ is already occurring. I think you can only limit it better by vaccinating.”

The more virus there is circulating, the greater the chance of dangerous variants

The Ministry of Agriculture, Nature and Food Quality is more cautious. “You cannot say in advance that a vaccine will reduce the amount of circulating virus,” says the spokesperson. “Before we start vaccinating in practice, with possible unforeseen consequences, that must first be sorted out. That is now happening in Wageningen. We also need that information to be able to set up a well-founded monitoring program.”

According to Mart de Jong, the current monitoring method is a reason not to vaccinate with sub-optimal vaccines in advance: “Poultry disease is now the indicator that there is an infection on a farm. If there is no disease after vaccination, but there is virus transmission, then there may ultimately be more spread.”

You can avoid that problem by adjusting the monitoring, says Kuiken: by screening for antibodies against the entire virus. “So we need to invest more in monitoring and biosecurity on farms,” he says. “And of course we have to take a critical look at those extremely high poultry densities in our country.”

Risks to humans

He mentions another argument for acting more quickly in all these areas: risks to human health. The virus variant that is now circulating in Europe has already infected people: one in England, one in the United States and two in Spain. In Asia, people die every year from the variant that is circulating there.

And the more virus there is circulating, the greater the chance that mutations will create a variant that easily jumps from person to person, or ‘mixes’ with the human seasonal flu virus, and can thus cause a pandemic. “We have seen that in the past,” emphasizes Kuiken. “The 1957 Asian Flu and the 1968 Hong Kong Flu are both linked to bird flu viruses.” Both pandemics claimed 1 to 4 million lives.

“Nevertheless, the Dutch government does not currently treat bird flu as a zoonosis,” says Kuiken, “so as a disease that can also affect humans. There is now an animal disease expert group that advises the ministry on this. But the other expert group, the zoonoses expert group, is not involved. In addition to veterinarians and biologists, this also includes doctors. So that group makes different considerations.”

Why doesn’t the government also call in that other expert group? “I call that cognitive dissonance,” Kuiken replies emphatically. “It’s easier to ignore that human side.”

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