Although California dairy farmers anticipated a bird flu mortality rate of less than 2%, some say between 10% and 15% of infected cattle are dying.

Based on genetic information of the virus, officials say it appears migratory waterfowl initially introduced H5N1 bird flu to dairy cows in late winter of 2023 in a single, isolated event. But genomic experts say wild birds are not continuing to spread the disease in cattle.

Two dairy workers in California have been infected with the state’s first human cases of bird flu, federal and state health officials said. The late Thursday announcement of two confirmed