US egg prices are soaring to record highs as farmers are forced to slaughter millions of chickens in an attempt to halt the spread of bird flu, which has ripped through the nation’s poultry barns in recent months.

A dozen eggs reached more than $8 in wholesale markets this week, more than double the price of a year ago and the highest ever recorded, according to Expana, a commodity price information service. Grocers including Walmart and Kroger have begun to ration purchases in certain cases. The Waffle House chain — a staple in the US south and Midwest — has tacked a surcharge of 50 cents an egg on to its dishes.

Supplies of fresh eggs are falling short as farmers cull millions of hens to control a variant of avian influenza that first emerged in a US commercial flock three years ago.