Tests on a father diagnosed with bird flu in China show he probably caught the disease from his dying son.
Scientists are concerned that if the virus evolves to pass easily from human to human millions could be at risk.
A genetic analysis of the Chinese case published in The Lancet found no evidence to suggest the virus had gained that ability.
But an expert has warned that failure to control outbreaks of disease in poultry is fuelling the risk to humans.
Note the word “easily.” It’s only a matter of time before the virus mutates to that point.