A pandemic is not inevitable, scientists say. But the outbreak has passed worrisome milestones in recent weeks, including cattle that may have been reinfected.

Since early 2024, the U.S. has logged 66 human cases of H5N1. Scientists are keeping a watchful eye on the virus’s spread as we enter a new year.

Bird flu's unprecedented spread among livestock and other mammals in the U.S. has raised fears that another pandemic could be in store. The incoming Trump administration will have to prepare for this risk. As H5N1 spills into more people and animals ...