An official wearing protective gear stands guard outside an entrance to a residential building in Hong Kong.Billy H.C. Kwok / Getty

HONG KONG—As the number of confirmed coronavirus cases exploded in China early this year, Hong Kong, densely populated and connected to the mainland, was able to largely contain the virus’s spread. A combination of community response and official action held back the pace of infections, with the number of patients discharged from treatment until recently outpacing those remaining in the hospital. This month, civil servants on work-from-home orders were allowed to return to their office. Soon, private businesses started to do the same. Commuters began to refill the buses and subways. Bars and restaurants left largely vacant for weeks saw patrons remerge. As reports of outbreaks abroad worsened, Hong Kong appeared to be slowly returning to form.

In recent days, this semblance of normalcy has vanished. The number of confirmed cases here has ticked upward at a much quicker pace than before, worrying health experts. The government reversed course on its easing of restrictions, sending workers back home, closing parks and city facilities, and reiterating calls for social distancing. It also introduced newer, more stringent measures, barring tourists and transit passengers from Hong Kong’s airport, one of the world’s busiest, and quarantining those who are allowed in. (A large portion of the recent confirmed cases are imported.) Another cluster of confirmed cases has been linked to bars and live-music venues, so gatherings of more than four people have been deemed illegal for the next two weeks; restaurants will reduce their capacity, and entertainment areas like cinemas and arcades must temporarily close.

Hong Kong and Singapore were early examples of places that were able to contain the spread of the virus, which causes the disease COVID-19, offering a model of sorts for countries elsewhere to follow (even if most did not take the cue). Yet now, this city is a different kind of model, a glimpse into what awaits the hundreds of millions of people living under restrictions in places such as Britain, France, Italy, and parts of the United States, wondering what life will look like once the virus is brought under control. The tightening and easing, as well as tweaking, of restrictions under way in Hong Kong, an effort to control the ebb and flow of the disease into manageable waves without letting it run rampant, illustrates how one protracted lockdown is unlikely to be sufficient as researchers take part in a global race to create a vaccine for the virus.

This tactic could keep health facilities from being overburdened, a reality now facing medical workers in New York City and parts of Europe, Gabriel Leung, who is one of the world’s experts on coronavirus epidemics and who worked extensively on the SARS outbreak and led Hong Kong’s response to the 2009 influenza pandemic, told me.

“The suppression-and-lift strategy is the most talked about amongst my ilk and in governments all over the world,” said Leung, who is also the dean of medicine at the University of Hong Kong. “You would need to keep on these control measures to varying degrees until one of two things happen: One, is there is natural immunity by active infection and recovery, or there is sufficiently wide availability of an effective vaccine administered to at least half the population, to create the same effective herd immunity. These are the only two ways of going about it.” Leung added that we’ll go through “several cycles” of tightenings and easings “before we will have resolution.”

Leung’s view is echoed in the scientific community. Research published by the COVID-19 Response Team at Imperial College London this month found that “intermittent social distancing—triggered by trends in disease surveillance—may allow interventions to be relaxed temporarily in relative short time windows, but measures will need to be reintroduced if or when case numbers rebound.” Writing for The Atlantic about how to cope with the virus in the United States, Aaron E. Carroll, a pediatrics professor, and Ashish Jha, a global-health professor, suggested a similar approach. “We can keep schools and businesses open as much as possible, closing them quickly when suppression fails, then opening them back up again once the infected are identified and isolated,” they wrote. “Instead of playing defense, we could play more offense.”

The aim of these measures, such as social distancing, is not to bring the number of people infected down to zero, Leung said; “that is not possible.” Rather, they are an effort to protect older people, who have a much higher risk of becoming infected and dying, as well as to keep health-care systems functioning. “No country, no population, no city can be spared from COVID-19,” said Leung, who is advising the Hong Kong government on its response to the virus. “The big question is, how do you make sure that you do not overwhelm societal functions? How do you make sure that your hospital system does not collapse? How do you make sure that there are enough ICU beds and ventilators for those who need them? How do you make sure that you can minimize the morbidity and mortality burden on your population while protecting the economy and the livelihood of the people on a sustainable basis? These are the big questions that any society would have to grapple with and have been grappling with.”

Leung was alerted to the new coronavirus by contacts in mainland China on December 31. His main concern at the time, he said, was the looming Chunyun—China’s spring festival, the largest human migration on the planet—set to begin just over a week later, on January 10. Wuhan, the epicenter of the virus, is a major transportation hub for China, a factor that caused particular consternation. As suspected cases began to emerge in countries popular with Chinese tourists, such as Japan and Thailand, Leung and his team were able to use airport, road, and train data to estimate the spread of the virus, telling reporters in Hong Kong on January 21 that the number of infected could be about 1,700 and that the virus had likely spread outside Wuhan across China. At the time, official Chinese figures put the number of cases at about 300. Leung said he received a call from the Chinese Center for Disease Control and Prevention the following day, and on January 23 arrived in Beijing with colleagues to assist with the first epidemiological study of the virus, published in The New England Journal of Medicine.

During the World Health Organization’s mission to China the following month, Leung said, he observed a three-pillared approach that was effective in slowing the spread of the virus. The first pillar, which he described as “medieval,” was rigorous quarantine and isolation of patients. This was coupled with a “very, very robust, excellent community organization,” including severe restrictions on social mixing and social mobility that were taking place on a neighborhood level. This was buttressed by extensive use of technology—apps, big data, artificial intelligence—to further track and record peoples’ movements.

Yet China, too, is being forced to impose a new wave of restrictions even as parts of life have appeared to return to normal. Beijing, fearing its own raft of imported cases that could reignite domestic spread, is implementing some of the tightest travel restrictions, barring practically all foreigners from entering the country as well as stopping nearly all international passenger flights. Since battling back the virus, authorities in Beijing have attempted to wrangle the narrative of the virus, sowing doubt over its origins amid tensions with the United States. Chinese officials attempted to silence doctors in Wuhan who raised early alarm about a mysterious virus and have cracked down on journalists covering the pandemic. And while China has begun to ease restrictions in Hubei province, where Wuhan is located, citing a drop in cases, reporting from various outlets in recent days has cast doubt on the validity of the figures, pointing instead to less testing being carried out, as well as the number of deaths attributed to the virus.

Leung said he couldn’t speculate about what was happening within China during the first weeks of the virus emerging, or about how other governments had handled outbreaks in their respective countries. Since he became involved in the response, Leung said his experience working with Chinese counterparts has been positive. During the WHO trip, Chinese officials were “very open, very transparent, a whole of government approach,” he told me. “Wherever we went, we were asking difficult questions and we were asking for the data, to look at the data and to discuss with their scientists, and they've been nothing but forthcoming.”

“China bought the rest of the world time,” Leung said. “Whether or not it could have brought it under control earlier and quicker is a different question … Whether different countries in the world have actually used that time well, I think it’s for their own people to judge.” As the newly reimposed restrictions in Hong Kong and parts of China illustrate, the West may have more lessons to learn.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.