Researchers have confirmed two cases of human to human transmission of the avian influenza virus, raising the possibility that the infection could soon gain a foothold among people, with the potential to strike millions.

The virus, influenza A (H5N1), infected 44 people last year (killing 32) in eight Asian countries. People normally catch this flu from infected birds, usually chickens and ducks. Health experts have been worried that the H5N1 virus could one day mutate into a formthat passes easily between humans, perhaps leading to a major flu pandemic to rival the Spanish flu of 1918.

Fearing that many countries would be ill prepared to deal with this potential threat, the World Health …