An outbreak of avian influenza, first detected in dairy cows in 2024, has spread to 860 dairy herds across 16 US states, affecting around 123 million birds. The outbreak, which has also led to the first human cases of the virus in the US, has led to an emergency declaration by California Governor Gavin Newsom to speed up the state's response. The US Centers for Disease Control and Prevention (CDC) has confirmed 61 human cases of the virus since April 2024, primarily in dairy farm workers.