A new strain of bird flu that transmits easily among wild birds has triggered an explosive spread into new corners of the globe, infecting and killing a variety of mammalian species and raising fears of a pandemic more lethal than COVID-19.

But the very changes that have allowed the virus to infect wild birds so efficiently likely made it less prone to infecting human cells, leading disease experts have said. Their views underpin global health officials' assessments that the current outbreak of H5N1 poses a low risk to people.

The new strain, called H5N1 clade, emerged in 2020 and has spread to many parts of Africa, Asia and Europe as well as North and South America, causing unprecedented numbers of deaths among wild birds and domestic poultry.