Researchers braced for a surge in 2022 that never came—and no one knows why.

2022 was the bad year that wasn’t—at least for a mysterious paralyzing condition in children.

In the decade before, hundreds of young, healthy kids in the US abruptly felt their limbs go weak. Debilitating paralysis set in. In recent years, around half of affected children required intensive care. About a quarter needed mechanical ventilation. A few died, and many others appear to have permanent weakness and paralysis.