The path of the latest variant of bird flu, this one called H5N2, has left a swath of tens of millions of dead birds throughout the Midwest. Egg-laying hens were especially hard-hit; in Iowa, for example, 25 million egg-laying hens were euthanized due to the disease. (There are, it’s worth noting, a few key things you can do to protect your own flock, if you have one.) The vaccine has already been tested on chickens, which is where that 100 percent figure comes from.
