By the time the 13-year-old arrived at the main children’s hospital in Vancouver, British Columbia, in early November, a bird flu infection had robbed her ability to breathe. Pneumonia shrouded her left lung.

At least 66 people, most of them dairy workers, have been infected. Last week, the Louisiana Health Department reported the country’s first human death from bird flu: that of a 65-year-old man who had exposure to a backyard flock.