CDC A(H5N1) Bird Flu Response Update June 14, 2024

At a glance

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

CDC update

June 14, 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. A 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 92 dairy cow herds in 12 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:

  • Finalizing flu serology studies to determine the population immunity among the U.S. general population to the A(H5N1) clade viruses causing outbreaks among animals in the United States.
    • CDC analyzed sera (blood) collected from people of all ages in all 10 HHS regions. Blood samples were collected during the 2022-2023 and 2021-2022 flu seasons. These samples were challenged with H5N1 virus to see whether there was an antibody reaction. Data from this study suggest that there is extremely low to no population immunity to clade A(H5N1) viruses in the United States. Antibody levels remained low regardless of whether or not the participants had gotten a seasonal flu vaccination, meaning that seasonal flu vaccination did not produce antibodies to A(H5N1) viruses. This means that there is little to no pre-existing immunity to this virus and most of the population would be susceptible to infection from this virus if it were to start infecting people easily and spreading from person-to-person. This finding is not unexpected because A(H5N1) viruses have not spread widely in people and are very different from current and recently circulating human seasonal influenza A viruses. Earlier analyses have found that A(H5N1) viruses are susceptible to influenza antiviral medications and that two existing candidate vaccine viruses (CVVs) would offer good cross-protection against A(H5N1) cattle outbreak viruses.
  • Continuing to support strategies to maximize protection of farm workers, who may be at higher risk for infection than others in the population.
  • 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 550 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.
  • 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.

Publication Highlights

Also, of note this week:

  • CDC published a new study that looked at whether the A(H5N1) virus isolated from a human case in Chile in 2023 causes and spreads disease through eye infection. The study found that the virus caused severe disease in ferrets infected following eye exposure. This study emphasizes the threat A(H5N1) viruses contribute to public health and demonstrates the value of studying nontraditional routes of virus exposure and wearing eye protection when working in potentially contaminated environments.

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.