An outbreak of Highly Pathogenic Avian Influenza (HPAI), Type A, subtype H5N1 was reported in dairy cattle for the first time on March 25, 2024 in the United States by the Center for Disease Control (CDC), and soon thereafter a human tested positive for H5N1 which was announced by the CDC April 1, 2024.

With this recent jump to an abundant mammal like cattle, there is concern that further evolution in the virus could result in it becoming easily transmittable between humans, a scenario that could result in a pandemic of the virus. This sort of zoonotic origin pandemic is not unprecedented, of course COVID-19 is believed to have made the jump from pangolins to humans and in a much more similar scenario, the 2009 H1N1 pandemic was caused by a virus similar to what was detected circulating in pigs, earning it the nickname “Swine Flu”. Both of these were declared a “Public Health Emergency of International Concern” (PHEIC) by the World Health Organization, with the H1N1 outbreak being declared a PHEIC on April 25, 2009 and COVID-19 declared a PHEIC on January 30, 2020. If an HPAI virus were to evolve to spread in sustained human-to-human transmission and become an outbreak, then there would be reason for the WHO to declare it a PHEIC.

Such a declaration would be a milestone prior to the the outbreak being considered a pandemic, as we saw with H1N1 and COVID-19.