This story is one in our six-part series The Pandemic Playbook. Explore all the stories here.

DAEGU, South Korea — Jo Hye-min stepped off the train and into a situation she had only seen in movies: a completely, and eerily, empty station.

It was February 2020, when the threat posed by the novel coronavirus SARS-CoV-2 was only starting to become clear in much of the world. But the situation in Daegu was already dire: Hospitals were overwhelmed and on the brink of collapsing. Hundreds of people believed to have been exposed to the virus were being isolated in private rooms. A nurse’s association in Daegu issued a plea for volunteers to help.

“It felt like war had broken out,” Jo says, and the 28-year-old nurse enlisted. The national disease control agency called her at 10 pm, asking if she could be in Daegu by 9 am the next morning. She dropped off her cat with a friend and made the 60-mile trip from her home in Busan. When she arrived at the isolation facility, she was told it would be at least a month before she could leave.

Jo was joining a frantic, all-out effort by South Korean officials to contain a burgeoning epidemic.

A woman in her 60s, who would later become known as Patient 31, had tested positive for Covid-19. Public health authorities learned she was a member of a secretive religious movement and attended services in the days before being diagnosed, potentially exposing more than 1,000 people.