South Korea amassed the world’s most comprehensive coronavirus data. What it’s taught us so far

March 19, 2020, 7:53 AM UTC

South Korea has the highest rate of coronavirus testing in the world, and we all may be better off because of it.

As of Wednesday, South Korea had tested over 295,000 people for the coronavirus, reporting over 8,500 infections with 81 deaths. In total, the country has tested over 5,000 people per million citizens, which represents the highest testing rate in the world. It dwarfs that of the U.S., which has tested about 100 people per million. In the U.S., the Centers for Disease Control officially reports the country has tested roughly 38,000 Americans, but the actual number is likely upwards of 82,000, according to the COVID Tracking Project, which has gathered state-level data.

“In epidemiology, we need to understand how much this virus is spread, who got it, and who did not,” said professor Ooi Eng Eong, an epidemiologist at the National University of Singapore. And thanks to South Korea’s extensive testing, the country has provided the world with a “useful picture” of the virus, said Ooi—even if it’s not quite the “whole picture.”

Data trove

South Korea’s data is valuable, in part, because it provides a stark warning to the world that there are likely far more young and asymptomatic carriers of the coronavirus than are currently being tallied, especially in countries like the U.S. that are suffering from ongoing testing shortages.

As of March 14, South Korea reported that nearly 30% of its confirmed coronavirus cases were in patients ages 20 to 29. In Italy, by comparison, 3.7% of coronavirus patients fell into that age range, according to a report from Andreas Backhaus, a research fellow at the Centre for European Policy Studies.

“South Korea has been testing basically everyone since the outbreak had become apparent,” Backhaus said. “Consequently, South Korea has detected more asymptomatic but positive cases of coronavirus than Italy, in particular, among young people.”

Limits of the data

There are, however, limits in using South Korea’s data as a model for how the coronavirus is spreading elsewhere. “It’s certainly a possibility that way more people are infected” with the coronavirus than are currently accounted for, said Ooi, but South Korea’s young population and health care system need to be considered when analyzing its coronavirus data.

South Korea’s population is young overall—age 43.7, on average—compared with a country like Italy, with an average age of 47.3. In Italy, the virus has hit older populations hard, spawning nearly 15,000 hospitalizations and almost 3,000 deaths so far. Italy’s outbreak among the elderly has overrun many of the country’s hospitals and led to a virus-related death rate of 8%. Roughly 1% of those in South Korea who’ve contracted the virus have passed away, according to Johns Hopkins University’s data portal.

Testing also does not account for a range of factors that determines the spread and severity of the coronavirus in a given country, such as government policies aimed at curbing the outbreak and the readiness of health care systems.

“Each country is approaching the problem slightly differently,” said Ooi. “It’s not comparing apples to apples at this stage.”

While South Korea’s data may provide insight into the nature of the virus itself, the country’s aggressive diagnostic measures are helping prove that widespread testing itself is an effective response. In late February and early March, South Korea reported the highest number of confirmed cases outside China, but in recent weeks the number of new cases has steadily declined, in part, because authorities have a grasp of who has the disease and who doesn’t.

“Testing at this moment helps you segregate those who are infected [from] those who are not, and stops transmissions within households and the community,” said Ooi. “Knowing the cases helps you remove those people from the community. Once you do that, then the number of exposures the case will have with non-cases will be reduced, and that is a well-known way to control the disease.”

More coronavirus coverage from Fortune:

How to prepare your personal finances for a coronavirus recession
—The coronavirus could upend America’s business relationships with China
—10 questions about the 2020 election during the coronavirus pandemic, answered
—3 months before the coronavirus, a war game showed we weren’t ready
—How hackers are exploiting the coronavirus—and how to protect yourself
—The coronavirus pandemic could mark a huge shift for the fitness industry
—Listen to Leadership Next, a Fortune podcast examining the evolving role of CEOs
—WATCH: The race is on to create a coronavirus antiviral drug and vaccine

Subscribe to Fortune’s Outbreak newsletter for a daily roundup of stories on the coronavirus and its impact on global business.