June 21, 2024 – CDC continues to respond to the public health challenge posed by a multistate outbreak of avian influenza A(H5N1) virus, or "H5N1 bird flu," in dairy cows and other animals in the United States. CDC is working in collaboration with the U.S. Department of Agriculture (USDA), the Food and Drug Administration (FDA), state public health and animal health officials, and other partners using a One Health approach. To date, there have been 3 human cases associated with an ongoing multistate outbreak of A(H5N1) in U.S. dairy cows. A Based on the information available at this time, CDC´s current H5N1 bird flu human health risk assessment for the U.S. general public remains low. All three sporadic cases had direct contact with sick cows. On the animal health side, USDA is reporting that 118 dairy cow herds in 12 U.S. states have confirmed cases of avian influenza A(H5N1) virus infections in dairy cows as the number of infected herds continues to grow.

Among other activities previously reported in past spotlights and still ongoing, recent highlights of CDC´s response to this include:

Posting an appendix to CDC´s interim H5N1 bird flu guidance to categorize the degree of risk among people at higher risk of exposure based on specific activities, from highest to lowest risk. This information will help public health officials and clinicians as they work with farm workers to assess risk and implement monitoring, treatment and testing recommendations.
Looking at the receptor binding profiles of recent avian influenza A(H5N1) viruses to see how well-adapted they are to causing infections in people (compared to birds). Humans and birds have different types and distributions of receptors to which influenza viruses can bind and cause infection. The hemagglutinin protein is responsible for the virus binding (or attaching) to host cells, which has to happen in order for infection to occur. For the receptor binding analysis of A/Texas/37/2024, the hemagglutinin (HA) surface protein of the virus was expressed in the lab and tested for its ability to bind to both human- and avian-type receptors. Preliminary results from these studies show that the A/Texas/37/2024 hemagglutinin only binds to avian-type receptors, and not to human-type receptors. This means the virus´s HA has not adapted to be able to easily infect people.