(Bloomberg) -- UK chickens and hens will stay indoors until the country’s worst-ever bird flu outbreak abates further. 

While risk levels are reviewed weekly, housing orders in place since November in England may not lift until spring, when wild birds that carry the virus migrate elsewhere, Chief Veterinary Officer Christine Middlemiss said Tuesday. That means free-range eggs — which typically account for more than half of supply — could soon be off the shelves.

The UK allows producers to keep the label for 16 weeks after housing orders are in place. That runs out near the end of February. Flu case counts have dropped from October, but the chance of infection remains “very high,” she said.

“We’re seeing less outbreaks, which is great, but the risk is still there,” Middlemiss said in an interview. “There’s a balance between bird welfare and the bird-flu risk level, and we have to look at what that balance is.” 

Read more: UK egg crisis shows food-supply crunches that won’t go away.

Still, the infection rate in wild birds has steadied and case counts on farms have also eased from an autumn peak. That’s a hopeful sign as global poultry producers battle an outbreak that has killed tens of millions of birds, particularly across North America and Europe. 

The UK also ordered birds indoors the prior year. Middlemiss said housing is a protective measure, although other factors can aid outdoor production, like ensuring new farms aren’t set up near waterways where wild birds gather. 

“Long term, I don’t think it’s the end of free-range production,” she said. “It’s very important to consumers. These have been remarkable and unusual outbreaks.” 

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