Why South Korea's coronavirus curve looks so different from the United States

• As COVID-19 spreads around the world, some countries' timelines look different from others.
• With a combination of contact tracing, testing, and isolating cases, along with other physical distancing policies, places like South Korea were able to reduce the size of its coronavirus outbreak and flatten the curve.
• But countries that didn't start testing and tracing early have had a harder time reducing the number of daily new coronavirus cases.
• For the latest case total, death toll, and travel information, see Business Insider's live updates here.
• Visit Business Insider's homepage for more stories.

Following is a transcript of the video.

Narrator: This graph shows the number of daily reported cases of COVID-19 for 10 countries. While some countries have been able to flatten the curve, others have seen exponential growth. Even when adjusted for population, some of these curves look very different. Reports have attributed these differences to three key factors: isolating cases, testing, and tracing cases.

So to better understand how each measure affects the curve, we decided to compare these four countries and their different responses. Why does South Korea have a bell curve while the US has a steep slope?

Let's zoom in, starting with China, the first country to be hit by the virus. Here's China's curve, but the crisis started well before these numbers peaked. On December 31, China reported to the World Health Organization that it was treating dozens of cases of pneumonia. A week later, a new type of coronavirus was identified, and the genome was mapped.

Later that month, China isolated Wuhan, the city where the virus was thought to have originated. A lockdown was then expanded to 36 million people. And during that time, China was building emergency hospitals and developing a rapid testing kit. By mid-February, over 700 million people were placed under travel restrictions or quarantine. And by the end of March, China had conducted over 320,000 coronavirus tests and had attempted to trace each of the 80,000-plus cases.

After a large outbreak, it was able to flatten the curve to the point where, earlier this month, China reopened Wuhan, over 10 weeks after the lockdown started and over 13 weeks after the first cases were reported. Its curve is unique, though, because it was the first country to deal with the virus, and the lack of public information and measures early on allowed the virus to spread. The eventual lockdown measures it took were particularly drastic, but in the meantime, the virus spread to other countries.

One country in particular has a curve that looks different than most. South Korea started developing COVID-19 tests before its first confirmed case. The country had put procedures in place for managing an outbreak after dealing with MERS in 2015, and it had a testing methodology ready even before the new coronavirus was identified.

By early February, South Korea's first test has been approved, and it used extensive contact tracing to identify the travel of each confirmed case, down to details like a person's seat number or what stop they got off the bus at. The data was anonymously posted online so people could check if they came in contact with a confirmed case. This became an important part of its strategy. Not only was it testing aggressively, but it was also contact tracing. Anyone who was thought to be infected could then be tested and isolated.

A month later, cases peaked, but over 100,000 people had already been tested. By late March, South Korea had tested three times that, and a social-distancing order banned large gatherings, further slowing the spread of the virus. Some experts say that by developing broad testing and contact-tracing measures before its number of cases spiked, South Korea was able to flatten the curve. The country is still reporting new cases, but compared to the over 900 daily cases during its peak, the outbreak is much more manageable. And social-distancing measures are still in place, further limiting the spread of the virus.

Let's look at Germany next. It had a test ready by mid-January. Four days later, Germany had its first confirmed case. It was able to start manufacturing tests by early February, allowing it to test about 120,000 people per week by early March, and it implemented several social-distancing measures later that month, closing schools, borders, and banning gatherings of more than two people. By late March, Germany was testing over 300,000 people per week.

As of April 8, Germany had tested more people than any other European country. This is due in part to its early testing and its use of contact tracing, which allowed testing to identify even the mildest cases of COVID-19. But case numbers have been high. As of April 10, Germany had the fifth-highest number of COVID-19 cases, but it has one of the lowest fatality rates in the world. Some experts think that Germany's expansive testing has kept the fatality rate so low. But not every country was able to start testing early.

The US currently has the highest number of confirmed COVID-19 cases in the world. Its first case was confirmed on January 21. And while we don't start to see a spike until March, that doesn't mean there weren't cases before that. They likely went undetected due to a lack of testing. According to the Associated Press, US government labs processed only 352 COVID-19 tests in all of February.

Testing only ramped up in early March, when the CDC started to allow private companies to develop their own tests. But for a while, tests were only available for people who had traveled from China or had a fever severe enough to be hospitalized, and the lack of contact tracing, quarantine, or physical-distancing measures exasperated the spread.

By March 11, over 100 colleges had canceled in-person classes, but major social-distancing steps didn't take place until mid to late March. Almost two months after its first case, a national emergency was declared. The White House and the CDC advised against large gatherings, and states like California and New York issued stay-at-home orders. But by then, the US was already seeing over 10,000 cases per day.

Now over 40 states have stay-at-home orders in place. But the US has been criticized for not implementing preventative measures early. It was slow to gather resources while the virus was spreading to other countries, and a botched rollout meant that testing didn't start to expand until mid-March. With little testing and hardly any contact tracing, the virus was able to spread silently throughout the country. The US is now testing over 100,000 people per day. But as of April 13, the US still had fewer tests per 1,000 people than South Korea. An earlier start in identifying and isolating cases could have prevented such a large outbreak.

In many countries, it's not just one measure that flattens the curve. It's the combination of isolating, testing, and tracing. Countries that have been able to do all three swiftly have been able to lower their number of new cases, but those that haven't will likely take longer to flatten the curve.

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