On Dec. 5, 2024, a study led by scientists at Scripps Research reveals that a single mutation in the H5N1 “bird flu” virus that has recently infected dairy cows in the U.S. could enhance the virus’ ability to attach to human cells, potentially increasing the risk of passing from person to person.

Currently, there are no documented cases of H5N1 transmitting between people: bird flu cases in humans have been linked to close contact with contaminated environments as well as infected birds (including poultry), dairy cows and other animals. However, public health officials are concerned about the potential for the virus to evolve to transmit efficiently between humans, which could lead to a new, potentially deadly pandemic.

The flu virus attaches to its host via a protein called hemagglutinin that binds to glycan receptors on the surfaces of host cells. Glycans are chains of sugar molecules on cell surface proteins that can act as binding sites for some viruses. Avian (bird) influenza viruses like H5N1 primarily infect hosts with sialic acid-containing glycan receptors found in birds (avian-type receptors). While the viruses rarely adapt to humans, if they evolve to recognize sialylated glycan receptors found in people (human-type receptors), they could gain the ability to infect and possibly transmit between humans. The findings were published in Science, highlight the need to monitor H5N1’s evolution.