NIH-funded study concludes that the risk of human infection remains low

A recent study published in Science and funded by the National Institutes of Health (NIH) has found that a single alteration in a protein on the surface of the highly pathogenic avian influenza (HPAI) H5N1 virus—currently present in U.S. dairy cows—could significantly increase its potential for human-to-human transmission.

These findings highlight the critical importance of ongoing surveillance and monitoring of HPAI H5N1 for genetic changes that might enhance its ability to spread among humans.

At present, the bovine (cow) H5N1 virus is not capable of human-to-human transmission. However, infections have been documented in individuals exposed to infected wild birds, poultry, dairy cows, and other mammals. As part of global pandemic preparedness efforts, researchers have long studied H5N1 to track natural genetic mutations and assess their potential impact on transmissibility.

Influenza viruses attach to cells with a surface viral protein called hemagglutinin (HA). The HA latches on to sugar (glycan) molecule receptors on cells to cause infection. Avian (bird) influenza viruses—like H5N1—have not infected people often because the human upper respiratory tract lacks the avian-type cell receptors found in birds. Scientists are concerned that viruses could evolve to recognize human-type cell receptors in the upper airways and acquire the ability to infect people and spread between them.

Laboratory Study on HA Protein Mutations

Scientists at Scripps Research used the H5N1 strain isolated from the first U.S. human infection with the bovine strain 2.3.4.4b (A/Texas/37/2024) to test how mutations in the HA gene sequence affected the binding of that protein with avian versus human-type cell receptors. The researchers introduced several mutations into the viral HA protein that had been observed to occur naturally in the past and found that one mutation, called Q226L, improved the ability of the protein to attach to receptors typically found on human cells, especially when an additional mutation was present. Importantly, the researchers introduced the genetic mutations only into the HA surface protein and did not create or conduct experiments with a whole, infectious virus.

The experimental finding with the Q226L mutation alone does not mean HPAI H5N1 is on the verge of causing a widespread pandemic, the authors note. Other genetic mutations would likely be required for the virus to be transmitted among people. In the setting of a growing number of H5N1 human cases resulting from direct contact with infected animals, the findings stress the importance of continued efforts at outbreak control and continued genomic surveillance to monitor for the emergence of HPAI H5N1 genetic changes and maintain public health preparedness.

Reference: "A single mutation in bovine influenza H5N1 hemagglutinin switches specificity to human receptors" by Ting-Hui Lin, Xueyong Zhu, Shengyang Wang, Ding Zhang, Ryan McBride, Wenli Yu, Simeon Babarinde, James C. Paulson and Ian A. Wilson, 5 December 2024, Science.
DOI: 10.1126/science.adt0180

The research was funded in part by NIH's National Institute of Allergy and Infectious Diseases (NIAID), through its Centers of Excellence for Influenza Research and Response program.

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