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 by what experts call untraceable “silent” transmissions.
“We’re getting better at having a large testing capacity, and we have a lot of resources for contact tracing, but the cycle repeats,” said Kwok Kin-on, an epidemiologist at the Chinese University of Hong Kong.
Compared with the United States and Europe, much of East Asia still has the virus relatively in check. Hong Kong, with a population of around 7.5 million, has had a total of 5,947 cases and 108 deaths, a low rate for any city.
But the recent setbacks underscore the challenges that the world will continue to face until there is a widely available vaccine. As cases have soared back to alarming levels in recent weeks, South Korea, Japan and Hong Kong have had to quickly recalibrate their strategies.
Travel bubbles that were announced with great fanfare are now on hold. Weeks after reopening, schools have been shut again. Bars and restaurants are closing early or shifting to takeaway menus.
“We need solidarity in this kind of situation, but as everyone knows, it’s not easy,” said Dr. Kim Woo-joo, an infectious disease specialist at Korea University in Seoul.
Complicating their efforts is the nature of the current outbreaks. Transmission is occurring not only in crowded venues like nightclubs, but also in settings like homes and workplaces where governments have fewer options to control people’s behavior.
On Thursday, South Korea recorded more than 500 new cases for the first time in about eight months. Experts say there doesn’t seem to be a single major cluster, as there was when churches and antigovernment protests drove earlier outbreaks.
Pandemic fatigue hasn’t helped. Medical personnel are exhausted, young people are bored because they can’t travel, and business owners are frustrated because they have to scale back or close early.
Kim Ill-soon, who owns a tea shop in a residential neighborhood of Seoul, said that her business had dropped off after the government this week barred people from dwelling inside cafes. Takeout is still an option, but for many people, chatting over tea in person is part of the draw.
“I’ve been busy apologizing to my customers for the last two days,” she said.
In Japan, the authorities have been reporting about 2,000 infections a day. Cases are spreading rapidly in Tokyo, which reported a record 570 infections on Friday, and around Osaka, Sapporo and other cities. Compared with summer waves, which mainly affected young people, the current one has hit many people in their 40s and older.
In a sign of the country’s alarm, Japan’s Imperial Household Agency said on Friday that it had decided to cancel Emperor Naruhito’s annual New Year event at the Imperial Palace in January — the first such cancellation since 1990, when the country was mourning the death of his grandfather.
“Please don’t underestimate coronavirus,” Dr. Toshio Nakagawa, president of the Japan Medical Association, told reporters on Wednesday in Tokyo. “We cannot let Japan become like the U.S. or Europe.”
The hope is that coronavirus vaccines will soon hand health officials around the globe a new weapon to beat the pandemic. But they won’t be widely available until the spring at the earliest.
Until then, and as winter approaches and caseloads soar, medical officials across much of East Asia are pleading for vigilance — and rethinking their pandemic policies.
In the spring and summer, the focus was mainly on fighting clusters at their source. Officials in Tokyo and Seoul, for example, responded to ones that had spread mainly from night clubs by temporarily closing down the venues. Hong Kong imposed restrictions on sea crews after a cluster was traced to cargo ships.
This time around, officials seem determined to take a more nuanced approach, apparently driven by concerns about the economic wreckage the pandemic has already caused. But doing so in face of such a pernicious pathogen can open up new challenges.
Hong Kong is rolling out a new contact-tracing app that would allow people to voluntarily scan QR codes on their smartphones when they visit a location, enabling officials to better tackle any clusters that emerge. But such apps have had limited success in South Korea, Britain and elsewhere.
It may be difficult to persuade many people to download the app unless the government provides more details about how personal information will be analyzed. The issue of data privacy is particularly sensitive in Hong Kong because the Chinese government has been tightening its grip on the territory.
“Hong Kongers are the most proactive in protecting themselves and their families, but they need to see proof of how the app would benefit them and ensure their privacy,” said Leung Chi-chiu, a respiratory specialist with the Hong Kong Medical Association.
The latest waves of infection have also forced governments to slow down their tentative efforts to open up.
Hong Kongers rushed to buy airline tickets to take advantage of a planned travel bubble with Singapore, even before the details were fully known. The special flights would have allowed residents in both places to avoid 14-day quarantines upon arrival.
The travel bubble was supposed to start this week. Then Hong Kong’s cases spiked, and officials postponed the start to Dec. 6.
In Japan, Prime Minister Yoshihide Suga has scaled back a roughly $ 16 billion campaign designed to encourage domestic tourism during the pandemic. But he has not scrapped it entirely, saying it helps to support local economies.
For people like Noriko Hashida, who sells cosmetics in Osaka, taking a vacation last week with eight of her work colleagues was worth the risk of infection.
Ms. Hashida said that a tourism subsidy from the government allowed them to spring for a luxury hotel that would have ordinarily been out of their price range. “We enjoyed it so much,” she said.
Still, they decided to cancel a sightseeing tour of the island because the optics were a little awkward.
“We thought that the local residents wouldn’t feel comfortable seeing visitors from Osaka, where infections are spreading rapidly,” she said.
Mike Ives and Tiffany May reported from Hong Kong and Makiko Inoue from Tokyo. Youmi Kim contributed reporting from Seoul, South Korea.
