June 7, 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. To date, there have been 3 human cases associated with an ongoing multistate outbreak of A(H5N1) in U.S. dairy cows.[1] Based on the information available at this time, CDC’s current A(H5N1) bird flu human health risk assessment for the U.S. general public remains low. All three sporadic cases had direct contact with infected cows. On the animal health side, USDA is reporting that 83 dairy cow herds in nine U.S. states have confirmed cases of 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 updated A(H5N1) Technical Report on June 5, 2024. This report updates an April 26, 2024, report to include three additional sporadic human cases of avian influenza infection (1 in Australia and 2 in the United States). The report also summarizes recent activity in wild birds, poultry, and other animals, including the multi-state outbreak in U.S. dairy cattle, and updated information on monitoring for human infections with highly pathogenic avian influenza A(H5N1) virus infections in the United States. People who have work or recreational exposures to infected animals are at higher risk of infection and should take precautions.
Posting a summary of the results from the ferret studies conducted by CDC on the A(H5N1) virus from the human case in Texas, on June 7, 2024.
Continuing work in the laboratory to characterize the virus from the second human case from Michigan. CDC was able generate a full genetic sequence for the neuraminidase, but only a partial genetic sequence of the hemagglutinin from the second human case in Michigan. No neuraminidase changes were identified that are associated with reduced antiviral susceptibility. The partial hemagglutinin sequence indicates that the virus remains primarily avian. There were no changes to the virus’ receptor binding site that would enhance its ability to infect and spread to or between people. There were no antigenic changes that would impact cross-protection of candidate vaccine viruses. Partial sequences have been uploaded in public databases (GenBank: PP861022; PP861023; GISAID: EPI3352528; EPI3352530).
Posting an NCIRD Bulletin that describes data from existing H5N1 seroprevalence studies. Although seroprevalence data to date are reassuring, it is important for CDC to continually assess the public health risk of viruses that have pandemic potential, like H5N1 bird flu viruses. CDC has protocols for seroprevalence studies related to the H5N1 bird flu virus outbreak in dairy cows and other animals in the Unites States.
Providing technical assistance to Michigan Department of Health and Human Services as the department plans to launch a serology epidemiology study of people exposed to sick cows.
Continuing to support strategies to maximize protection of farm workers, who may be at higher risk for infection than others in the population. On May 30, CDC launched digital outreach efforts aimed at farmworkers in affected communities to increase awareness of the risks of A(H5N1) and recommended preventive actions. Static English Meta (Facebook and Instagram) placements in the first week delivered more than 1 million impressions in affected counties. Spanish language Meta launched on Thursday, June 6, delivering nearly 2,500 impressions within the first hour in market. Digital display and local radio placements are forthcoming.
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 500 people have been monitored as a result of their exposure to infected or potentially infected animals, and at least 45 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 | Avian Influenza (Flu) (cdc.gov).
As part of plans to maintain enhanced surveillance over the summer, CDC will maintain sequencing and testing through the National Influenza Reference Center laboratories and the Influenza Sequencing Centers (ISC). These are centers that serve as an extension of CDC’s laboratory and conduct testing and sequencing on samples from public health laboratories.
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.