The team found that human cells have a strong barrier that prevents bird flu viruses from infecting them. This barrier is a protein called IFITM3, which is found on the surface of human cells.

IFITM3 works by blocking the entry of bird flu viruses into cells. It does this by binding to the virus and preventing it from fusing with the cell membrane. This prevents the virus from entering the cell and replicating.

The researchers also found that this barrier is stronger in human cells than in animal cells. This may explain why bird flu viruses are more likely to cause illness in animals than in humans.

They are not as easily able to penetrate the human cell barrier. This could be a key factor in why relatively limited human-to-human transmission of bird flu is observed."

While this discovery provides insight into the limited transmission of bird flu among humans, it is essential to continue monitoring outbreaks, as viruses constantly evolve, and there's always the possibility that mutations could affect their transmissibility or virulence