Policy Backgrounders

Bird Flu Outbreak: H5N1 Spreads to Cattle

May 09, 2024

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H5N1 bird flu, which the Centers for Disease Control (CDC) describes as “widespread” around the world, including in the US, has been devastating wild and domestic bird populations since 2022. For the first time during this spike in infections, bird flu has transmitted to cattle, with the virus infecting 36 dairy herds in nine states. A Texas dairy worker who caught bird flu in late March from an infected cow marks the second ever reported case of the virus in humans in the US and demonstrates the virus’s ability to transmit between mammalian species.

• As of May 8, H5N1 infections have been reported in poultry in 48 states and in 36 dairy herds in nine states. While the US Department of Agriculture (USDA) first reported the virus on March 25, a recent analysis of genomic data by USDA’s Animal Disease Center revealed that the highly pathogenic H5N1 virus was likely circulating in dairy cows for four months before it was identified.
• According to the CDC, the risk of general transmission of the virus to the public remains low; however, the agency anticipates additional sporadic human infections because of the potential for influenza viruses to evolve rapidly and the wide global prevalence of H5N1 viruses.
• Federal health officials have already begun efforts to develop a vaccine to protect people in the case that the H5N1 virus mutates significantly enough to permit easy human-to-human transmission. As of now, the US stockpile includes two vaccines made from older, similar strains of the virus, but experts are concerned about the whether those vaccines would remain effective against the strain currently circulating in the US.