To protect its flocks and its foie gras from the ravages of bird flu, France has begun a mass vaccination of 64 million ducks.

The campaign, which started this week, aims to prevent the spread of a deadly variant of avian influenza that has forced French farmers to cull more than 30 million birds in the past three years, contributing to a downturn in the production of foie gras.

“A real glimmer of hope,” Éric Dumas, a duck farmer and the president of France’s foie gras federation, said in a statement after the agriculture minister, Marc Fesneau, visited his farm near Bordeaux to inaugurate the campaign.

But the bird vaccination program, which Mr. Fesneau described as the first in the European Union, has led to a quick reaction from the United States, which said it would restrict imports of ducks and other poultry from Europe. “France’s decision to vaccinate presents a risk” of introducing the disease into the United States, the U.S. Agriculture Department said.

In recent years the disease, known as Highly Pathogenic Avian Influenza, or HPAI, has spread through poultry farms across the globe, causing the deaths of nearly 60 million farmed birds in the United States alone.

In France, farmers had already tried to counter the spread of the flu by adding health checks, reducing the density of birds on the farms and culling. In 2022, those efforts led to a 35 percent drop in the number of ducks available to produce foie gras compared with the year before, according to the foie gras committee.

Marie Pierre Pé, the foie gras federation’s director, said in a phone call that the vaccine program was fundamental for the farmers in her group. “We’ve paid a heavy price for the avian flu,” she said. “We are going to protect the animals.”

Foie gras is the term for the liver of a duck or goose that has been fattened by forced feeding. For many the dish is a hallmark of French gastronomy; others say that the way it is produced constitutes torture and animal cruelty.

The French government’s vaccination program will be compulsory for farms that have more than 250 ducks, which taken together account for 64 million birds. That figure exceeds the number of people who received the coronavirus vaccine in France — and, like many of the Covid vaccines, this one will also require two doses.

The first vaccination shot will be administered to 10-day-old chicks, followed by a second one eight days later. The campaign, which will extend into next year, will be “a real technical and financial challenge,” the foie gras federation said in a statement.

Jocelyn Marguerie, an avian expert from France’s national network of veterinarians working with farm animals, said his group had helped plan the program with the government. He said ducks had been picked because they catch the virus easily, and spread it fast.

The government will cover 85 percent of the program’s cost, at about 80 million euros (about $84 million). That is a fraction of the more than a €1 billion the government paid in 2021 and 2022 to compensate farmers who had been required to cull their birds, according to a recent French parliamentary report.

Public health authorities, concerned that bird flu could mutate into a version that can be transmitted to humans, have accelerated efforts to limit the outbreaks.

The Agriculture Department’s action was announced Sept. 29. The restriction covers imports of poultry, live ducks, duck eggs and untreated duck products from Europe. The announcement said the restriction stemmed from France’s decision to vaccinate ducks, because vaccinated poultry may not show signs of bird flu, thus masking whether the virus is circulating.

The French Ministry of Agriculture said in a statement that talks between the two countries had begun “to provide all the elements of reassurance which will allow the American restrictions to be quickly lifted.”

Ms. Pé said the ban would not hurt French foie gras producers, because they do not have a license to export to the United States.

Mr. Marguerie, the avian vet, said that veterinarians would also still be deployed to ensure that no contamination occurs despite the vaccinations, taking random swabs of the ducks.

“If we find they are positive,” he said. “They will be eliminated.”