With Europe and the United States locked in deadly battle with the coronavirus that causes Covid-19, a number of countries that were hit early by the virus are doing a far better job of beating it back.

China, which is now diagnosing more cases in returning travelers than in people infected at home, reported no new domestically acquired cases on Wednesday, for the first time in more than two months. South Korea, which had an explosive outbreak that began in February, is aggressively battering down its epidemic curve. Singapore, Hong Kong, and Taiwan have together reported only about 600 cases.

Those successes have been bought by a layering of what are known as non-pharmaceutical initiatives including social distancing and travel restrictions aimed at severing chains of transmission to keep the virus from going into an exponential growth cycle.

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None of the other countries has been as aggressive as China, which put tens of millions of people into forced quarantine for weeks. And these other locales have not all adopted an across-the-board checklist of measures. While kids in Hong Kong havent been in school since late January, class continues in Singapore.

Heres a look at some of the techniques these governments employed, and how they stack up to steps being taken in the United States as well as the United Kingdom, which has come under heavy scrutiny for its approach, fairly or not.

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The island city-state was one of the first places to ban incoming flights from the Chinese city of Wuhan, where the virus originated. And it placed people coming into the country from countries affected by Covid-19 into mandatory quarantine.

Singapore has seen its numbers gradually tick up. But it hasnt had an explosion of cases, likely because it has aggressively tracked where the virus was circulating. Of the 345 cases it has recorded, 124 have recovered and 221 are considered active cases. It has not yet recorded a death.

Singapore has done everything right, said David Heymann, who led the World Health Organizations response to the 2003 SARS outbreak and now teaches infectious diseases epidemiology at the London School of Hygiene and Tropical Medicine. Theyve been openly communicating every day on whats going on. And theyve made it clear to the population and the population understands that they are not only to protect themselves but protect others.

Health authorities have severed several transmission chains, tracking down people who have been in contact with a known case and ordering them into home quarantine. They are checked twice daily to see if they developed a fever.

Mass gatherings were canceled. Schools have not been closed, though students go through temperature screening to enter. So does anyone entering most buildings or restaurants.

Heymann, who was in Singapore recently to lecture at Duke-NUS Medical School, said at the start of each class, a picture would be taken of the classroom, so that if any student became ill, there would be a record of who had been in close contact with him or her. So theres all kinds of innovations and measures going on, he told STAT.

Singapore also quickly developed a much-needed serology test a blood test used to look for antibodies in blood that are a sign of previous infection. Getting a handle on how many people have been infected is critical to understanding how deadly this virus really is, experts stress. Authorities in Singapore actually used the serology test in late February to find the source of a cluster of cases in a church group.

Hong Kong, like Taiwan and Singapore, bears deep psychological scars from the 2003 SARS outbreak. Hong Kong had the most cases of the disease outside of mainland China and people there remember the trauma that came with it.

So do their public health leaders, who have prepared for disruptive infectious diseases outbreaks in the years since SARS and the 2009 H1N1 flu pandemic. People take respiratory health hygiene seriously, routinely wearing surgical masks in public if they are sick to prevent spread to others.

These places were better equipped to face an outbreak of the new coronavirus than many others, Ben Cowling, a professor of infectious diseases epidemiology, and Wey Wen Lim, a graduate student in infectious disease epidemiology at the University of Hong Kong, wrote in a recent opinion piece in the New York Times.

Hong Kong responded very quickly within days of Chinas Dec. 31 announcement that it was finding unusual cases of pneumonia. Doctors were told to report any patient who had influenza-like illness and a travel history to Wuhan. Borders crossings into China were closed first some, then all.

Schools and universities havent been open since the Lunar New Year, on Jan. 23, though online learning has replaced classroom teaching in some circumstances.

Hong Kong has been testing for the virus, aggressively trying to locate cases. People have been urged to telework if possible and to practice social distancing.

Gabriel Leung, dean of medicine at the University of Hong Kong, said measures have largely worked, but the toll is high. And both he and Cowling are concerned people are starting to let down their guard.

I think we are already beginning to see a little bit of response fatigue among the people, Leung said, noting it has become apparent over the past couple of weeks. You see that people are beginning to mix again, theyre beginning to come out again, because its been two months already. So how do you still keep alert and keep this up? There is only so much that any population would be able to tolerate.

Taiwan didnt move initially to cut off air travel with Wuhan, as Singapore did. But doctors boarded incoming flights with temperature scanners looking for people who were unwell. Later it did ban most flights from China.

Mass gatherings were not banned, but were discouraged. The government controlled the distribution and pricing of medical masks, Cowling and Lim wrote. Stiff fines up to more than $30,000 were threatened for people who violated home quarantine orders.

All of these places are coupling aggressive testing strategies to identify cases, with isolation, contact tracing and sometimes quarantine of at-risk people, said Caitlin Rivers, an assistant professor of epidemiology at the Johns Hopkins Center for Health Security, speaking of Singapore, Taiwan, Hong Kong, and South Korea. And they have also layered on community mitigation strategies, school closures and other closures. So what I take away from that is that its important to layer these strategies to try to accommodate both of them.

Rivers tried to look at whether the measures were being successful at driving down new infection rates by pulling up data on other types of communicable infections, both respiratory illnesses, diarrheal diseases, and conjunctivitis. In a short analysis she posted on Twitter, Rivers noted that rates of these other infections declined after stringent social distancing practices were put into place.

The things that are also spread through close contact have fallen dramatically, and so that tells me its individual-level social distancing behavior that is contributing to the control, she said.

Indeed, the Republic of Korea has had a different trajectory than Hong Kong, Taiwan, and Singapore.

The new coronavirus took root in a large and closely knit religious sect, a development that led to an explosive outbreak, which the other three have not experienced. As of Wednesday South Korea has reported just over 8,400 cases and 91 deaths.

But whereas Western countries that have reached numbers like those see daily and every larger rises in their case counts, South Koreas outbreak curve has been beaten back. From a one-day high of 909 new cases on Feb. 29, South Korea has seen its daily case count rise by as few as 74 cases on Monday. That swung back up, though, on Thursday to 152.

The country is testing aggressively more than a quarter of a million people had been tested by March 15, Foreign Minister Kang Kyung-wha told the BBC recently.

Testing is central because that leads to early detection. It minimizes further spread and it quickly treats those found with the virus, she said, suggesting early detection and treatment may explain why South Koreas death rate is lower than other places with large numbers of cases.

South Korea introduced drive-through testing, allowing people to be checked for disease without even leaving their vehicles. Travelers returning from abroad have to provide contact information and report their health status for 14 days after their return via a mobile app, the South Korea CDC website reports.

It has recommended Koreans refrain from international travel at this time and urged people to avoid large gatherings and church services. Companies have been encouraged to allow workers who are able to work from home.

Many epidemiologists and mathematical modelers who have been plotting the possible trajectory of this pandemic think there is no choice but to try some of the serious social distancing measures other countries have taken.

But Marc Lipsitch, an infectious diseases epidemiologist at Harvards T.H. Chan School of Public Health, said the possibility of containment stopping spread through rigorous tracing of all contacts of known cases is not realistic. That window has closed, he said.

I think one thing to learn from those experiences is that whats appropriate when an epidemic is small and mostly ascertained is not appropriate when an epidemic is large and mostly not ascertained, he said.

I would say put in place as intense as possible social distancing and get the messaging from the White House consistent with that, Lipsitch said. Right away, everywhere, with the short-term goal of trying to reduce the demand on the health care system.

Any universities still in session should send students home, especially those living in dormitories which are one step away from cruise ships in terms of density and poor ventilation, he said.

Lipsitch said time is limited to make a difference.

The data that we just assembled from Wuhan about the timing and magnitude of the peak demand for critical care shows first that it can very quickly even without that many people being infected compared to the whole population exceed per capita bed capacity in the United States, Lipsitch said.

He noted there was a four-week lag between the shutdown of Wuhan and the overwhelming of critical care units. So if you wait till you see a problem, then you have another month of agony, at least.

It appeared that was the kind of message Britain was not heeding.

There was a huge controversy late last week when it seemed like the country intended to simply allow enough people to become infected so that the population would develop herd immunity.

Adam Kucharski, an associate professor of infectious diseases epidemiology at the London School of Hygiene and Tropical Medicine, said it was never the governments plan to drive toward herd immunity; rather, there was an acknowledgment that might be what happens because the virus could be so hard to control.

Its not been an aim to get everyone infected as soon as possible. Its more this really tough situation weve got where the options we have are probably not going to be able to fully control this in the long term, Kucharski said.

The country has now taken a swing toward the types of early and aggressive social distancing methods other countries are trying to implement. The government is urging people with even mild symptoms to self-isolate; but Kucharski worried that message was going unheard in the din about herd immunity.

The country, he said, was trying to save some of the more difficult measures really stringent social distancing approaches that are hard to sustain over time for closer to when they are needed.

It makes sense to use them, given that theyre short-term measures, use them when theyve got the most impact, Kucharski said. You cant shut down your country for months.

Rivers suggested that was a risky approach. I think thats a difficult thing to time. My recommendations for the U.S. context at least, is to begin social distancing measures early, she said.

In the United States, a tepid early response marked by a prolonged delay in ramping up testing and a White House that initially seemed intent on playing down the scale of the threat has given way to a war footing.

This week the White House urged Americans to embrace social distancing by not taking part in gatherings of more than 10 people. In a number of communities, restaurants are closed to all but takeout or delivery service. Some states have closed schools. The country is on edge.

But with large-scale testing capacity still coming up to speed, it remains unclear how deeply the virus has embedded itself into the country, and whether the measures people and their local, state, and national governments are trying to adopt can slow the coronavirus progress.

It is also unclear how long communities can sustain the dramatic lifetime changes that appear to be needed to slow the viruss spread.

Right now people are approaching this if they are basically sheltering in place for a Minneapolis blizzard, lasting two or three days. And thats the mindset that they have. Where, in fact, we need to look at this like a coronavirus winter, where were only in the first weeks of what could be a long season, warned Michael Osterholm, director of the University of Minnesotas Center for Infectious Diseases Research and Policy.

This could last easily many months. And we need to make our actions proportional to the risk in the community or else we run the risk of people just getting tired of them when that particular community has not seen increased transmission of the virus.

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Understanding what works: How the coronavirus is being beaten back - STAT