IEEE Spectrum Nextstrain can’t predict where the virus is going next. But it can tell us where new cases of the virus are coming from. That’s crucial information for health officials globally, who are trying to determine whether new cases are arriving in their countries through international travel, or being transmitted locally. By comparing the genetic codes of viral samples taken globally, it’s possible to construct a map of the virus’s mutations as it moves around the world. That’s what Nextstrain does. “We rely on the presence of these naturally occurring genetic mutations to inform our visualizations of the virus’s spread,” says Hadfield. Nextstrain charts a virus like a family tree, or evolutionary timeline. For coronavirus, that family tree originates in the Chinese city of Wuhan, and branches out from there. When new cases pop up, the genetic code of those viral samples can be compared to those in the database to determine its region of origin. For example...