Overview

• H5N1 bird flu has infected over 900 dairy cattle herds in 16 U.S. states, with California declaring a state of emergency due to widespread cases.
• The first U.S. human death from H5N1 was reported in January 2025, and genetic mutations in the virus are raising concerns about its potential to spread between humans.
• Two distinct H5N1 subtypes are circulating: B3.13 primarily in cattle and D1.1 in poultry, with the latter linked to more severe human cases.
• Researchers emphasize the need for stronger biosecurity measures, improved testing strategies for cattle, and vaccine deployment for high-risk workers.
• Government response to the outbreak has been criticized as insufficient, with experts warning that prolonged circulation in mammals increases the risk of a human-adapted strain.