CDC data’s “explicit purpose” is to guide researchers toward the places and people who most need attention, Patrick Sullivan, an epidemiologist at Emory University and a former CDC Epidemic Intelligence Service officer, told me. As the changes unfold before him, he said, “it’s hard to understand how this benefits health.”

Key information and datasets have vanished from the US Centers for Disease Control and Prevention’s websites, alarming epidemiologists, other scientists and concerned American citizens.