France ordered that a third dose of vaccine against avian influenza be applied on ducks in areas most at risk, citing "new scientific evidence" as it aims to avoid a surge in outbreaks, Reuters reported, citing the farm ministry on Wednesday.

France had raised the risk level of avian influenza to 'high' from 'moderate' on Tuesday after new cases of the disease were detected, forcing poultry farms to keep birds indoors.

"New scientific evidence has led us to adjust the vaccination protocol to guarantee the best possible protection of animals and avoid any epizootic outbreak," the ministry said in a statement.

"For this, a three-dose protocol will be applied from (this week) until March 15, 2024 in areas identified at risk and targeting mulard ducks," it added.

Mulard ducks are used for foie gras.

Four outbreaks of highly pathogenic avian influenza, commonly called bird flu, have been detected since Nov. 27, the first ones this autumn, including three in Brittany in western France and one in the Somme in northern France.

These were all on turkey farms. There has been no outbreak reported among ducks so far.

By Nov. 19, 6.9 million ducks had received a first shot of bird flu vaccine and 3.6 million had received two, the ministry said.

Germany's Boehringer Ingelheim, which had been selected to produce the vaccine, was not immediately available to comment.

Although avian influenza is harmless in food, its spread is a concern for governments and the poultry industry due to the devastation it can cause to flocks and a risk of human transmission.

The spread of the virus has led to the culling of hundreds of millions birds worldwide in recent years. It usually strikes during autumn and winter and has been spreading in many European countries over the past weeks.