May 12, 2020 8:49 AM EDT

South Korea has been hailed for its effective handling of an early outbreak of the coronavirus and held up as a model to show how it’s possible for democratic government to beat back the virus. But, a new flare-up in infections is threatening to derail that success.

Officials began relaxing some social distancing restrictions in early May as new case numbers dwindled to just a few a day. But dozens of new cases have been confirmed in the last week, nearly all of them linked to nightclubs in the Itaewon district of Seoul. Authorities have been on high alert since a 29-year-old man who visited several bars and nightclubs in early May tested positive. He is believed to be at least one of the individuals behind the new cluster. More than 100 people have tested positive and some 5,500 may have visited bars and nightclubs in the area around the same time as infected individuals.

Experts say clusters like the one in South Korea could become the new normal as countries—including the U.S.—try to balance brining the pandemic under control with restarting their economies. What’s important, experts say, is that South Korea has an effective system in place for bringing new outbreaks under control, and the flexibility to tighten restrictions again when needed.

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“It is likely that we will see cycles of easing of restrictions, then tightening again, until we have reached population levels of immunity that would be protective—either from a vaccine or from enough people being infected, recovering and developing long-term, durable immunity,” says Dr. Gavin Yamey, the director of the Center for Policy Impact in Global Health at Duke Global Health Institute.

The new outbreak in South Korea shows that all countries, even once they have controlled their epidemics, must remain vigilant. Already, in other places where the virus looked to be contained, new cases have begun popping up. In the central Chinese city of Wuhan, where the virus is believed to have originated, five new locally-transmitted cases were reported on Monday and officials announced plans to test all 11 million residents.

“A single case anywhere could lead to an outbreak,” says Yamey. “It is likely that countries will continue to experience outbreaks and will probably need to re-apply social distancing measures as a ‘fire extinguisher’ to bring cases down again.”

South Korea never enacted the type of strict lockdown that many western countries did. When an outbreak linked to a mysterious religious sect exploded in late February in the city of Daegu, officials in the country of 52 million managed to flatten the curve with a robust public health response based on extensive testing and tech-powered contact tracing, aided by social distancing and public cooperation. Case numbers remained under 11,000, and fewer than 260 people died.

Early this month, the country shifted from a strict social distancing policy, which asked citizens to cancel gatherings, events and travel and refrain from going outdoors, to a “distancing in daily life” strategy, with the aim of moving the country a step closer to normalcy. The new guidelines ask individuals to take precautions like staying at home for several days if they are sick, keeping a distance of two arms’ lengths with other people and washing their hands for 30 seconds.

But given the new wave of infections, officials have tightened restrictions once again. Seoul’s mayor on May 9 ordered all bars and nightclubs closed indefinitely. Plans to reopen schools have been delayed.

Soonman Kwon, a professor in the school of public health at Seoul National University, tells TIME that it’s too early to say how worrying the Itaewon nightclub cluster is, but some ups and downs are inevitable given the nature of the virus.

“We need to be well prepared for these type of small, small spikes because we cannot suddenly make it to zero,” he says.

Still, there are reasons to be concerned about the new outbreak. Kwon says that contact tracing for the Itaewon nightclub cluster may prove more difficult than for the February outbreak tied to the the Shincheonji sect. As infections soared earlier this year, authorities obtained a list of about 200,000 members of the church, facilitating their search for those who might be infected.

Before they were shuttered over the weekend, many bars and clubs in Seoul required patrons to have their temperatures taken and leave their name and phone numbers to enter—but some revelers left false or incomplete information. Officials in Seoul said they had only been able to get in touch with about 2,400 of the approximately 5,500 people who visited the affected area, according to local media. Authorities said they would try to track the remaining people with credit card records and police assistance.

Read More: Asia Is Slowly Beginning to Reopen Travel. Here’s What the World Could Learn

Adding to the difficulty, some South Korean media outlets reported that the cluster is linked to “gay clubs.” Stigma may cause those who visited the area to avoid coming forward—LGBTQ people face widespread discrimination in South Korea, according to Human Rights Watch. Authorities have introduced “anonymous testing” to encourage people to come forward, requiring only a phone number and not a name.

“Many of the visitors of the club who have not been identified may be reluctant to come out, so tracing may not be complete as before,” Dr. Sung-il Cho, a professor of epidemiology at Seoul National University, tells TIME.

But experts say that the system South Korea used to tackle its initial outbreak should help it successfully get on top of the latest outbreak.

“Fortunately, South Korea has been a world leader in establishing a high quality system to test, contact trace, isolate infected people, and quarantine exposed people,” says Yamey, “so they will be quickly able to control this outbreak.”

Please send tips, leads, and stories from the frontlines to virus@time.com.

Write to Amy Gunia at amy.gunia@time.com.

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