Data insight

South Korea’s sudden upswing

Cases in South Korea are rising at a pace previously unseen among peers


South Korea is experiencing a dramatic surge in cases that is completely unparalleled among its peers. Other countries in the East Asia & Pacific region (and elsewhere) are experiencing a rise in cases too (as this companion post shows), but the scale of the surge in South Korea appears to be in a different league – both in terms of slope and absolute volume.  

A look at the data

As of May 18, the country registered a positivity rate of 21.3%, which has led to a dramatic rise in cases. The impact on mortality has remained contained so far.

To frame the escalation of cases, let’s make a quick comparison with the UK and the US. The two charts below show daily cases per capita (weekly averaged) and cumulative cases per capita (since the start of the pandemic). As we can see, the daily numbers are well above anything the UK or the US have experienced so far. The experience of South Korea is also astonishing when we consider the cumulative numbers covering the full period of the pandemic thus far. In merely a few weeks have cumulative cases per capita in South Korea caught up to ~2/3 of what it took the UK and the US two years to accumulate.

The unprecedented escalation of cases in South Korea is the result of the more transmissible Omicron variant. As seen elsewhere, the mortality impact in a well-vaccinated population remains limited. South Korea is close to 90% fully vaccinated and over 60% boosted. Even so, given high transmissibility, mortality numbers are going up. Luckily, however, Omicron is not Delta.

How unparalleled is this?

So far we have compared South Korea with the UK and the US. Let’s make a few broader comparisons now to illustrate the uniqueness of South Korea. Let’s first look at the weekly trends (showing numbers for the last 7 days now).

The first chart compares South Korea with ALL countries of the world (click on the chart for a higher-resolution version). The red line traces South Korea and the blue lines map the trajectories of the full universe of 196 countries minus 1 (Korea). 

The recent spike on the cases side is clearly unprecedented even though its height has been replicated in recent (Omicron) history in a few other countries. On the mortality side, South Korea is again on the high side, even though this is far from unique even as we consider the more recent period in which countries were affected by Omicron.


South Korea has a population of 52 million people. So it is fair to make a comparison that controls for absolute population size. We can think of two reasons why that is important. First, smaller countries tend to be more dense, especially on the lower end of the population size spectrum, and density tends to facilitate spread and thereby raise infection prevalence, keeping all else equal. Second, viruses spread from person to person; they’re not infecting everyone uniformly at the same time. Geography matters. Compare for example China with Hubei and Hubei with Wuhan at the height of their crises at the beginning of the pandemic. As we progress to geographically smaller units, the per capita numbers tend to be higher when outbreaks are concentrated.

In the chart below, we compare South Korea with other large countries in the world. We set the cut-off at 20 million people, which leaves us with a total of 60 countries exceeding the cut-off. As we can see, South Korea is a total outlier when it comes to cases. It is also an outlier when it comes to mortality at the current time, but not from a historical perspective.

Next, we narrow the sample further to large countries that fall in the group of high-income countries. As this website has argued repeatedly, the income classification of the World Bank is a useful instrument to examine the differential impacts of the pandemic as countries exhibit different vulnerabilities depending on whether they are rich or poor. They also demonstrate different capabilities in correctly measuring the impacts. For this reason, let’s compare South Korea with its peer group of high-income countries and focus just on those high-income countries with a population over 20 million. In total that gives us 13 countries. 

The conclusions are similar. South Korea remains an all-time outlier when it comes to cases and on the mortality side is it a current outlier but there are several large high-income countries that have indeed done worse, including in the more recent period of Omicron. 

Finally, let’s repeat the above analysis and apply it to the cumulative numbers. We can see that there’s been a dramatic catch-up on the cases side, especially when we consider South Korea’s peer group of large countries. Thankfully, on the mortality side, the numbers remain low in international comparison. That is because South Korea has managed to keep mortality at minimal levels prior to the current outbreak and because it has achieved high levels of primary and booster vaccination at the time of Omicron. 

We should caveat the above discussion by noting that countries of course differ in terms of testing, where the overall availability of tests is a factor as is the question whether the results of rapid at-home tests find their way into the statistics. South Korea’s has recently expanded rapid test efforts, which is likely to tilt the results upwards somewhat compared to other countries. 
The developments in South Korea are reminiscent of what is happening more broadly in the EAP region. The region includes several countries that have managed to contain or suppress the virus very well until Omicron came. Luckily South Korea was well prepared in terms of its vaccine coverage levels, which helped compensate for the fact that the vast majority of its population did not acquire immunity through prior infection.