So far, the H5N1 virus isn't transmitted between people — but the CDC has found a mutation in a human case "concerning."

The fate of a Canadian teenager who was infected with H5N1 bird flu in early November, and subsequently admitted to an intensive care unit, has finally been revealed: She has fully recovered. But genetic analysis of the virus that infected her body showed ominous mutations that researchers suggest potentially allowed it to target human cells more easily and cause severe disease — a development the study authors called “worrisome.