They Beat Back the Virus (Again and Again and Again)

HONG KONG — First, it was travelers and university students bringing the coronavirus back to Hong Kong from Europe and the United States. Then, sea crews and bar patrons were the ones spreading infections.

In the latest wave, a large cluster appears to have started in ballroom dancing halls that are popular with older women, then progressed to other dancing venues and banquet-style restaurants.

For much of the year, every time Hong Kong beat back a surge of coronavirus cases, new problems would pop up weeks later, in other places and among other populations.

Similar patterns hold true in other parts of Asia that are still fighting day-by-day battles to keep their Covid-19 rates from spiraling out of control. And the latest waves of infection are proving harder to trace than earlier ones were — just as winter forces more people indoors and raises the risks of transmission.

Japan and South Korea are experiencing some of their highest single-day tallies since the pandemic began, driven largely by diffuse clusters in the Tokyo and Seoul metropolitan areas. Although still below its peak for the year, Hong Kong is facing a surge on par with its summer wave, driven in large part