A deadly bird flu outbreak has wreaked havoc on U.S. chicken farms, claiming the lives of over 20 million egg-laying chickens last quarter, marking the worst impact on America's egg supply since the outbreak began in 2022.

U.S. Department of Agriculture (USDA) data shows the staggering toll included chickens culled to contain the virus, too. This, in turn, has contributed to record-high egg prices across all production types, including conventional, cage-free, and certified organic systems, a USDA report published on Jan. 10 shows.

The federal government has spent $1.25 billion compensating farmers for chickens lost to bird flu since the outbreak began, aiming to encourage farmers to report infections and help stop the virus from spreading, a news release from CBS News states.

Why Bird Flu Cases Are High Now

Bird flu cases surge during winter as migrating wild birds carry the virus south — cooler weather helping it spread.

This winter, the virus has spread beyond poultry, spilling into dairy herds. Hundreds of infected herds have been linked to contaminated raw milk, which spreads through farmers' clothing, equipment, and other animals shared between farms.

California has been hit especially hard, prompting the state to declare a state of emergency.

While the outbreak has devastated poultry populations, the Centers for Disease Control and Prevention (CDC) has only reported 66 human cases of bird flu in the U.S. since the virus emerged, with most infections being mild and occurring in farm workers with close contact to infected animals.

However, one tragic fatal case was recently reported in Louisiana, linked to the D1.1 strain of the virus that has been spreading in wild birds.

Despite this, researchers believe the strain responsible for the many human infections has mutated to be less severe in humans compared to other strains circulating in the wild.

And Vaccines?

The USDA announced plans to stockpile a new poultry vaccine targeting the D1.1 strain of the virus. However, officials say widespread vaccination is unlikely due to concerns it could hide symptoms, potentially disrupting international poultry exports.

The virus has already spread to humans and pets through contaminated products. In two separate incidents, raw pet food made from infected animals was linked to the deaths of cats in California and Oregon.

"All recent detections of H5N1 [bird flu] in cats had these things in common: the infected cats ate wild birds, unpasteurized milk, raw poultry, and/or raw poultry pet food," a Food and Drug Administration spokesperson told CBS News.