The CDC reported ongoing response efforts to the H5N1 bird flu outbreak, which has affected dairy cows, poultry, and other animals in several states. Since April 2024, the CDC has confirmed 70 human infections linked to exposure to infected animals. Importantly, there has been no evidence of person-to-person transmission. While the immediate risk to the public remains low, the CDC continues to monitor the situation, as influenza viruses evolve quickly.1
Of the 70 confirmed human cases, 67 involved individuals exposed to infected dairy cows or poultry. Three cases had undetermined exposure sources. As of February 24, 2025, the CDC confirmed three new cases, a dairy worker in Nevada, a poultry worker in Ohio, and a backyard poultry owner in Wyoming. Clinical findings reveal varying illness severity, while the dairy worker in Nevada recovered from mild conjunctivitis, the poultry workers in Ohio and Wyoming experienced severe illness and were hospitalized, though both are now recovering at home.1
The CDC sequenced the viruses from the Nevada and Wyoming cases, finding notable mutations in the virus’s PB2 protein. The Wyoming case exhibited the E627K mutation, linked to more efficient replication in mammals, while the Nevada case showed the D701N mutation, associated with more efficient replication in mammalian cells. These mutations have been seen in previous human cases from Texas (2024) and Chile (2023). Although, neither mutation was found to affect the efficacy of antiviral medications or the current H5 vaccine candidate. The virus from the Ohio case has yet to be sequenced.1
Despite most infections being mild, the CDC notes that serious illnesses, including one death, have occurred. The CDC continues to urge those with exposure to infected animals to follow preventive measures, including avoiding contact with potentially infected animals and following CDC guidelines for minimizing exposure.1
