From Tuesday to Thursday, the United States recorded more than 8,000 deaths from covid-19. It was the deadliest three-day period on record, surpassing the record of 7,701 set from April 14 to 16. Then, New York City hospitals were overwhelmed as efforts to contain the virus had only recently been put into place. Now, more than nine months after the virus was first detected in our country, this three-day span was 5 percent higher.

The toll on Thursday alone was 2,753. In South Korea, where the virus was first detected on the same day as it was in the United States, the covid-19 death toll is 536.

Total. Since January. More people have died in the United States over five hours on Dec. 3 than have died of the disease in South Korea overall.

While South Korea was seeing more new cases as a function of population in February and early March, by St. Patrick’s Day the United States took the lead. We have not relinquished it since. (Numbers for this article come from Our World in Data.)

The last time the population-adjusted rate of new cases in the United States was less than twice that of South Korea was March 18. The last time we were seeing less than 10 times as many new cases as a function of population was March 23. Over the past month, we’ve averaged 100 times as many new cases per resident each day, even as South Korea has seen an increase in its daily case totals.

There has been a lot written contrasting the response to the virus in South Korea with the response in the United States, but there’s one obvious factor at play: testing. President Trump likes to tout the massive number of tests conducted by the United States, but we conduct so many tests in part because the virus remains uncontained. South Korea has conducted far fewer total tests in part because its system of isolating and containing infections is far more effective, obviating the need for broader testing.

(The smoothed data on testing shows a drop-off that appears to be related to missing data in recent days. We’ve indicated that drop with a dotted line.)

While both the United States and South Korea detected their first cases on Jan. 20, South Korea moved much more quickly to expand testing. You can see it on the chart above, with that little blip in early March. The United States’ slow expansion of testing was in part a function of production problems that contaminated early efforts.

We’ve never really caught up to the number of tests conducted by South Korea as a function of cases. In March and November, South Korea conducted about 48 tests for every detected case, the lowest monthly figures the country saw. In the United States, we’ve never conducted more than 22 tests for each confirmed case, according to this data.

South Korea has other advantages, too. Its only land border is with North Korea, which is among the most strictly controlled borders in the world. South Korea also had recent experience with a highly contagious respiratory disease, MERS, which helped boost cultural familiarity with wearing face coverings to protect against infections.

Part of it, too, has been the response. The government’s effort to track and contain outbreaks has been effective, in part leveraging personal data, which might raise privacy objections in the United States.

Its research, though, has offered repeated insights into the nature of the virus. Sociologist Zeynep Tufekci on Friday highlighted a remarkable study from the country that demonstrates how central that airflow is to the likelihood of infections. (You are strongly encouraged to read the full article, incidentally, given its disconcerting revelations about the risks of indoor spaces.)

Reading the study, she writes, “is an exercise in what it means to do a study really, really well, with the resources of a government that’s committed to generating useful information.”

The consistent link between new coronavirus cases in this country and covid-19-related deaths has meant that the death toll has risen and fallen in sync with new infections.

The last time the United States saw fewer recorded covid-19 deaths in one day than did South Korea was Nov. 8. Since April 1, the United States has recorded more deaths in a single day than South Korea has over the course of the pandemic 204 times.

Since Jan. 20, 515 Americans have died from covid-19 for every South Korean who has. The population of the United States is less than seven times that of South Korea.