In the summer of 2014, a passenger landed with a fever at the airport in Lagos, Nigeria — a city of more than 20 million. At that time, neighboring countries were in the middle of what would become the largest Ebola outbreak ever, so health workers were deeply concerned.
"We were in the middle of a tragedy, on the precipice of a cataclysm," says Pardis Sabeti, a computational geneticist at the Broad Institute. "It could be unstoppable."
