Now Omicron is here and Ms. Lim—like contact tracers around the world—is doing less, despite confronting more cases than ever before.

Daegu now reports thousands of cases a day—more than it had combined during the first year and a half of the pandemic. Yet, Ms. Lim is no longer trying to halt outbreaks in their tracks by poring through security-camera footage, credit-card records and phone GPS records.

Instead, she tracks confirmed cases at nursing homes. She goes home at 6 p.m. most nights.

At her City Hall office, Ms. Lim sits at a desk beneath a banner that reads, “Daegu Omicron Response Headquarters.” But she often finds herself wondering: “Can I really stop tracking these cases?”