Across China, the virus that could spark the next pandemic is already circulating. It’s a bird flu called H7N9, and true to its name, it mostly infects poultry. Lately, however, it’s started jumping from chickens to humans more readily–bad news, because the virus is a killer. During a recent spike, 88% of people infected got pneumonia, three-quarters ended up in intensive care with severe respiratory problems, and 41% died.