I work with veterinarians who research influenza—the flu—in Ohio. They spend days at county fairs taking nasal swabs from pigs and blood samples from people who work with pigs. They follow the spread of disease from animals to people and from people to animals. Pigs that get the flu run fevers, become lethargic, and sometimes have respiratory symptoms, just like people. Veterinarians often recommend vaccinating animals to prevent flu and other diseases.

More than 10 years ago, these veterinarians told me a pandemic was due. They expected something like the 1918 flu, which caused millions of deaths worldwide. They thought an influenza outbreak would start in animals and move to people—a typical zoonotic disease.