Thousands of miles from Dr. Barney Graham’s lab in Bethesda, Maryland, a frightening new coronavirus had jumped from camels to humans in the Middle East, killing 1 out of every 3 people infected. An expert on the world’s most intractable viruses, Graham had been working for months to develop a vaccine but had gotten nowhere.

Now he was terrified that the virus, Middle East respiratory syndrome, or MERS, had infected one of his lab’s own scientists, who was sick with a fever and a cough in fall 2013 after a pilgrimage to the holy city of Mecca in Saudi Arabia.

A nose swab came back positive for a coronavirus, seeming to confirm Graham’s worst fears, only for a second test to deliver relief: It was a mild coronavirus, causing a common cold, not MERS.