May 24, 2024 – CDC continues to respond to the public health challenge posed by a multistate outbreak of avian influenza A(H5N1) virus, or “A(H5N1) virus,” 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. On May 22, CDC reported an additional human case of avian influenza A(H5) virus infection in a dairy worker in Michigan who had work exposure to infected cows. By May 23, the agency had confirmed the neuraminidase of the virus as N1. This is the second human case associated with the ongoing A(H5N1) outbreak in dairy cows, and the third case reported in the United States.[1] Based on the information available so far, this infection does not change CDC’s current human health risk assessment for the U.S. general public, which the agency considers to be low.[1] CDC continues to support strategies to maximize protection of farm workers, who may be at higher risk for infection than others in the population. On the animal health side, USDA is reporting that 63 dairy cow herds in nine U.S. states have confirmed cases of A(H5N1) virus infections in dairy cows.

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

Supporting Michigan as they follow up with their investigation.
Beginning work in the laboratory to characterize the virus from the human case from Michigan this week. This includes:
CDC has sequenced the influenza virus genome identified in a specimen collected from the person in Michigan. This is a highly pathogenic avian influenza A(H5N1) virus from clade 2.3.4.4b that is >99 percent identical to the viruses that are circulating in dairy cows. A preliminary technical assessment of the genetic sequence is posted separately. The genome will be publicly posted in GISAID and submitted to GenBank on May 24.
Attempting to recover the virus from the human case in Michigan. Isolating or growing this virus in egg or cell cultures (known as “virus isolate”) will allow for further virus characterization efforts including, assessing changes in antigenicity compared to vaccines, and learning about the severity and transmissibility of this virus.
If virus isolation is successful, experiments with a virus isolate will include conducting the following:
assessment of vaccine elicited antibody cross-reactivity with the virus isolate,
antiviral susceptibility testing to determine in vitro if the virus from the human case in Michigan is susceptible to flu antiviral medications that are used to treat flu, and
animal and cell experiments to assess the transmissibility and pathogenicity of the virus.
More information and results will be shared when available.
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 350 people have been monitored as a result of their exposure to infected or potentially infected animals, and at least 39 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 as needed.
Developed and posted new consumer and responder resources, including a summary fact sheet of CDC recommendations and resources and an information sheet for dairy farm workers, outlining how infections with A(H5N1) might happen and how to prevent them. Spanish language and other translations are forthcoming. CDC also posted two graphics showing how bird flu is spreading.
Continuing to monitor flu surveillance data, 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.
Also, this week, CDC was informed by FDA that it has authorized the use of the CDC H5-test for use with conjunctival (eye) specimens. This means that public health labs can now conduct testing on eye specimens themselves initially instead of having to forward these to CDC. Confirmation testing is still required at CDC.

Publication Highlights
Also, of note this week:

The World Health Organization published an antigenic characterization report of A(H5N1) viruses isolated from dairy cows and the first dairy farm worker in the United States, compared to clade 2.3.4.4b candidate vaccine viruses (CVVs). Based on current genetic, antigenic, and epidemiologic data, WHO found that no new CVVs were needed at this time.
A new CDC report published in JAMA on May 21, 2024, summarizes the results of a survey that found that nearly all U.S. states and territories had taken measures to detect cases of A(H5N1) viruses in poultry, to monitor people exposed to infected poultry, and to test those exposed persons with flu-like symptoms, pointing to a preexisting level of public health preparedness for A(H5N1) viruses. The survey, conducted in collaboration with the Council of State and Territorial Epidemiologists (CSTE), occurred before the A(H5N1) virus infections were detected in dairy cows in multiple U.S. states.
On May 24, 2024, CDC published a MMWR report describing the federal response to the multistate outbreak of A(H5N1) virus in dairy cows in the United States. The report details response activities as well as related challenges. The discussion section of the report summarizes some of the challenges Federal partners face in this response.
CDC Recommendations
As a reminder, CDC recommends that:

People should avoid close, long, or unprotected exposures to sick or dead animals, including wild birds, poultry, other domesticated birds, and other wild or domesticated animals (including cows).
People should also avoid unprotected 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.
People should not drink raw milk. Pasteurization kills A(H5N1) viruses, and pasteurized milk is safe to drink.
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.

Footnotes
[1]The first human case of A(H5N1) bird flu in the United States was reported in 2022 in a person in Colorado who had direct exposure to poultry and was involved in the depopulating of poultry with presumptive A(H5N1) bird flu. The 2022 human case was not related to dairy cows. The person only reported fatigue without any other symptoms and recovered. Learn more at: U.S. Case of Human Avian Influenza A(H5) Virus Reported.
The second human case of A(H5N1) bird flu in the United States was reported on April 1, 2024. This case in Texas was the first human case of A(H5N1) bird flu in the United States linked to an outbreak in dairy cows and was also the first likely case of human infection with A(H5N1) from a cow globally. The person reported eye redness as their only symptom, consistent with conjunctivitis, and has recovered. Learn more about this case in a letter published in the New England Journal of Medicine titled Highly Pathogenic Avian Influenza A(H5N1) Virus Infection in a Dairy Farm Worker.
On May 22, 2024, a human case of A(H5N1) virus infection was reported by Michigan. This is the third human case of A(H5) bird flu in the United States and the second human case related to the multistate outbreak of A(H5N1) in dairy cows. As with the human case from Texas, the individual is a worker on a dairy farm where A(H5N1) virus had been identified in cows. The patient only reported eye symptoms. Learn more at: CDC Reports Second Human Case of H5 Bird Flu Tied to Dairy Cow Outbreak