As the world stares down months of potential shutdowns and mounting medical battles to save coronavirus patients, everyone is trying to figure out how to best move forward.

A growing body of examples and data from different countries is beginning to give researchers a sense of what works. China, on the one hand, put 16 cities in complete lockdown for more than two months, while South Korea threw its weight behind widespread testing efforts. Sweden told its population to wash their hands and keep far apart, and the US seems to initially have waited before rolling out large-scale responses.

As the outcomes become more clear in each country, many experts are pointing to a strategic combination of widespread testing, quarantining, and nationwide lockdowns to fight the virus' spread.

Here are the four main approaches governments have taken, and how successful they've been.

1. Testing, isolation, contact tracing, and quarantine

south korea coronavirus 3
south korea coronavirus 3
Ahn Young-joon/AP

In countries where officials caught the first cases early enough, governments could adopt a "containment" approach, rather than scrambling to mitigate an outbreak that was already spiraling out of hand.

"Case finding, isolation, contact tracing, and quarantine: that's the four things for containment," Dr. Ben Cowling, an epidemiologist at the University of Hong Kong who researches influenza transmission and control measures, told Business Insider.

That's what South Korea did. Health officials quickly started testing tens of thousands of people per day and opened the first COVID-19 drive-thru testing facilities. The government also implemented a robust (though potentially privacy-invading) contact-tracing program: After tests reveal a positive case, officials use interviews, GPS phone tracking, credit-card records, and video surveillance to trace that person's travel history, according to The Washington Post .

South Korea's daily rate of new cases declined in early March, and since then the curve of the virus' spread has somewhat flattened.

Similarly, Hong Kong and Singapore quickly implemented widespread testing, travel restrictions, quarantines of known cases, and social-distancing measures starting in late January. Both saw success in quickly containing their outbreaks.

thermometer scan hong kong coronavirus
thermometer scan hong kong coronavirus
REUTERS/Hannah McKay

But these strategies may not be feasible everywhere.

"Hong Kong's a small place. Seven million people, very developed, very good healthcare system, and central laboratories that can do a lot of testing. But for the US, it's not really comparable," Cowling said.

To succeed with containment, he added, US authorities would have had to implement widespread testing in every state, picking up even the mildest cases. With such a large population, this approach requires a lot of resources.

"Containment fails at the point when you run out of manpower, because there's too many cases to do the contact tracing and the quarantine," Cowling said.

But when containment is impossible, there are a few other options.

2. Waiting before rolling out large-scale responses

Trump
Trump
Mandel Ngan/AFP via Getty Images

"Other countries, I think Europe and America, didn't seem to appreciate that what happened in China was going to happen in Europe and the US as well, because it seemed a long way away and different," Cowling said.

Two regions in Northern Italy Lombardy and Veneto clearly demonstrate the consequences of that approach.

The two took different tacks: Veneto imposed travel restrictions early and started testing all residents who had come into contact with coronavirus patients, even if they weren't showing symptoms. Lombardy, however, tested only residents who showed symptoms and had difficulty enforcing a regional lockdown.

Nearly a month later, data indicated two different outcomes: Veneto has seen a slower rate of increase in new cases and deaths than Lombardy.

"Hope is not a strategy," Mike Ryan, an epidemiologist and the World Health Organization's head of emergencies, told NPR . "We are still very much in the up cycle of this epidemic."

Read more: The top scientist at J&J told us how the $350 billion pharma giant will have a coronavirus vaccine ready at 'warp speed', then pump out 1 billion doses

In the US, government agencies have been criticized for their slow response to the coronavirus' threat. Errors and delays in producing the CDC's coronavirus test led to dangerous shortages, and decisions about lockdowns have been left to states in piecemeal fashion.

"This is such a rapidly moving infection that losing a few days is bad, and losing a couple of weeks is terrible," Ashish Jha, director of the Harvard Global Health Institute, told Bloomberg . "Losing two months is close to disastrous, and that's what we did."

Coronavirus test
Coronavirus test
Jim Urquhart/Reuters

Testing in the US is finally ramping up, resulting in a surge of confirmed cases across the country : The total jumped from 32,000 on March 22 to over 210,000 on Friday.

"We're slowly starting to catch up, but we're still behind," Jha said. "The only shot we have, I believe, of staving off the worst is going to a national quarantine for 14 days."

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, has said the US will see "millions of cases" and more than 100,000 deaths .

3. A nationwide lockdown

Wuhan on lockdown 2
Wuhan on lockdown 2
Costfoto / Barcroft Media via Getty Images

"Lockdown" isn't a technical term used by public-health officials, but it can refer to mandatory quarantines, recommendations to stay at home, closures of certain types of businesses, or bans on events and gatherings.

Dozens of countries have adopted these strategies. More people are currently under some form of lockdown than were alive during World War II .

In China, that seems to have worked. The country has seen a sharp drop-off in its rate of new cases, though some locals and US officials have disputed the country's reported numbers.

Countries that began their nationwide lockdowns in March like Italy, France, and Spain still appear to be in the upswing of their outbreaks.

france lockdown paris eiffel tower police
france lockdown paris eiffel tower police
BENOIT TESSIER/Reuters

In the US, most states have now issued stay-at-home orders , and early data seems to suggest the measures are working in some places .

But lockdowns are not a permanent solution. As some Asian cities and countries have begun to lift their restrictions, they're seeing a rise in new cases .

Hong Kong's outbreak consisted of just 100 cases at the beginning of March; the city had implemented widespread social distancing, work-from-home rules, public-information campaigns, and high-tech case mapping. On March 2, civil servants went back to their offices. Private businesses followed, and people began commuting and going to restaurants and bars again.

Two weeks later, as residents who had been abroad began returning home, Hong Kong's cases more than doubled. As of March 30, the city had reported more than 680 cases.

The Hong Kong government has responded by reinstating the lockdown and layering in new restrictions. It sent workers back home, banned gatherings of more than four people , and barred nonresidents from entering the city.

hong kong airport coronavirus protective hazmat suit
hong kong airport coronavirus protective hazmat suit
Tyrone Siu/Reuters

"This is a pattern playing out across parts of Asia mainland China, Singapore, Taiwan that were among the first to tackle the outbreak," the CNN analyst James Griffith wrote March 23. "All are now introducing new restrictions as a sudden wave of renewed cases begins to crest."

That's why lockdowns don't really stop the spread of an infectious disease, according to Cowling. They only delay it.

"They can shut down for a month, but then when they reopen, they're still going to have an epidemic starting again, and I don't see the long-term plan for those locations," he said. "Are they going to just cycle? Just down one month in every three months?"

4. Public information campaigns

medical coronavirus virus flu sick cold hygiene hand sanitizer clorox hands wash cleaning bacteria cox 8
medical coronavirus virus flu sick cold hygiene hand sanitizer clorox hands wash cleaning bacteria cox 8
Crystal Cox/Business Insider

Some countries that haven't instituted lockdowns and quarantines instead have encouraged residents to social distance and wash their hands regularly.

In Sweden, schools and many businesses remain open. The government has been stressing hand washing, social distancing, and protecting seniors, but ultimately the choice has been left to the individual.

"We are trying to slow the spread enough so that we can deal with the patients coming in," Anders Tegnell, a lead epidemiologist at the Public Health Agency, told The New York Times . "That's the way we work in Sweden. Our whole system for communicable disease control is based on voluntary action."

On Wednesday, Sweden's Public Health Agency put new guidelines in place that mandate every person "keep a distance" from others.

Public information campaigns can help flatten the curve, slowing an epidemic enough to remain within the capacity of a nation's hospitals. But they are likely insufficient on their own.

"I think they play a role," Cowling said. "Getting people to change their behavior is important because it can slow down transmission."

Despite their different approaches, Sweden's numbers are not so far off from its neighboring countries that are in full lockdown. As of Friday, about 0.06% of Sweden was infected, compared to 0.07% of Denmark's population, and 0.1% of Norway's population.

Combining measures makes a 'suppression' strategy

San Francisco coronavirus
San Francisco coronavirus
Reuters/Shannon Stapleton

An analysis from Imperial College London, published March 16, recommended a blend of these preventive measures.

"We conclude that the effectiveness of any one intervention in isolation is likely to be limited, requiring multiple interventions to be combined to have a substantial impact on transmission," the authors wrote.

The report highlighted two fundamental coronavirus strategies: mitigation, "which focuses on slowing but not necessarily stopping epidemic spread," and suppression, "which aims to reverse epidemic growth."

Suppression would save the most lives, they said. That involves nationwide social distancing, widespread testing, and quarantining identified cases.

Writing in The Atlantic , Ashish Jha and Aaron E. Carroll, a professor of pediatrics Indiana University, also recommended suppression.

"To achieve this, we need to test many, many people, even those without symptoms," they wrote.

coronavirus test kits.JPG
coronavirus test kits.JPG
REUTERS/Mike Segar

The catch is that to truly prevent the worst, this strategy has to remain in place until a vaccine becomes available, which could take about 18 months. It's unlikely that governments, or the populations they oversee, could sustain nationwide lockdowns for that long.

That means that countries and territories will likely have to strategically lift and reinstate restrictions.

"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," Jha and Carroll wrote. "Instead of playing defense, we could play more offense."

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