CDC A(H5N1) Bird Flu Response Update June 21, 2024

At a glance

CDC provides an update on its response activities related to the multistate outbreak of avian influenza A(H5N1) virus, or "H5N1 bird flu," in dairy cows and other animals in the United States.

CDC Update

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.
Chart avian vs human-type receptors showing virus maintains a preference for avian-type receptors
How well the A(H5N1) virus HA binds to avian-type, but not to human-type receptors is shown in the graph. Results from these studies indicate that this virus maintains a preference for avian-type receptors and is not adapting to be able to infect people.
  • Continuing to support strategies to maximize protection of farm workers, who are at higher risk of infection based on their exposures. This includes outreach to farm workers in affected counties through Meta (Facebook and Instagram), digital display, and audio (Pandora). These resources provide information in English and Spanish about potential risks of A(H5N1) infection, recommended preventive actions, symptoms to be on the look-out for, and what to do if they develop symptoms. Since May 30, when English assets launched, Meta outreach has generated more than 3 million impressions. Spanish Meta assets launched on June 6, and since then have garnered nearly 400,000 impressions. Additionally, CDC continues to create additional materials, including fact sheets in K'iche' and Nahuatl, in addition to Spanish.
  • Continuing to support states that are monitoring people with exposure to cows, birds, or other domestic or wild animals infected, or potentially infected, with avian influenza A(H5N1) viruses. To date, more than 690 people have been monitored as a result of their exposure to infected or potentially infected animals, and at least 51 people who have developed flu-like symptoms have been tested as part of this targeted, situation-specific testing. Testing of exposed people who develop symptoms is happening at the state or local level, and CDC conducts confirmatory testing. More information on monitoring can be found at Symptom Monitoring Among Persons Exposed to HPAI.
  • Continuing to monitor flu surveillance data using CDC's enhanced, nationwide summer surveillance strategy, especially in areas where A(H5N1) viruses have been detected in dairy cows or other animals for any unusual trends, including in flu-like illness, conjunctivitis, or influenza virus activity.
    • Overall, for the most recent week of data, CDC flu surveillance systems show no indicators of unusual flu activity in people, including avian influenza A(H5N1) viruses.

CDC Recommendations

As a reminder, CDC recommends that:

  • People should avoid exposures to sick or dead animals, including wild birds, poultry, other domesticated birds, and other wild or domesticated animals (including cows), if possible.
  • People should also avoid exposures to animal poop, bedding (litter), unpasteurized ("raw") milk, or materials that have been touched by, or close to, birds or other animals with suspected or confirmed A(H5N1) virus, if possible.
  • People should not drink raw milk. Pasteurization kills A(H5N1) viruses, and pasteurized milk is safe to drink.
  • People who have job-related contact with infected or potentially infected birds or other animals should be aware of the risk of exposure to avian influenza viruses and should take proper precautions. People should wear appropriate and recommended personal protective equipment when exposed to an infected or potentially infected animal(s). CDC has recommendations for worker protection and use of personal protective equipment (PPE).
  • CDC has interim recommendations for prevention, monitoring, and public health investigations of A(H5N1) virus infections in people.

Following these recommendations is central to reducing a person's risk and containing the overall public health risk.

In addition to limiting interactions between infected animals and people, containing the outbreak among animals also is important, which underscores the urgency of the work being done by USDA and animal health and industry partners.

This is a rapidly changing situation, and CDC is committed to providing frequent and timely updates.

  1. The first human case of A(H5N1) bird flu linked to an outbreak in dairy cows in the United States was reported on April 1, 2024, in Texas. It was also likely the first human infection with A(H5N1) from a cow globally. A second human case associated with the dairy cow outbreak was identified in Michigan on May 22, 2024. A third human case associated with the dairy cow outbreak was identified in Michigan on May 30, 2024. None of these three cases are associated with the others. These cases were actually the second, third, and fourth human cases of A(H5N1) ever reported in the United States. The first human case of A(H5N1) bird flu in the United States was reported on April 28, 2022 in a person in Colorado who had direct exposure to poultry and who was involved in depopulating poultry with presumptive A(H5N1) bird flu. The 2022 human case was not related to dairy cattle. The person only reported fatigue without any other symptoms and recovered.