>South Korea's naive case fatality rate (CFR) is already 120 deaths/9037 cases
But the denominator in this formula strongly depends on who and how often you test. In other words: You don't know the number of cases.
Obviously, people who are severely affected are tested more often. People with mild or no symptoms might never be tested, even if they want to (I'm not sure about South Korea but for sure this is happening in Germany).
Based on people in the German parliament and the German soccer league, you can currently guestimate that 1% of the population is already infected (1% of the parliament and 1% of the premier league players are infected. I suspect that they are tested more often and even without symptoms. Maybe they have more contact to other people - maybe not).
Yes, this is a wild guess, but much better than taking the confirmed cases which are heavily biased towards people where the infection causes problems.
Yes, all my figures above are Case Fatality Rate (CFR) and not Infection Fatality Rate (IFR), which includes people with mild or no symptoms. It's much harder to estimate the latter unless one conducts antibody tests on a sufficient sample of a population. South Korea's extensive testing program should bring their two figures closer than those of other countries.
Credible estimates of IFR from noted epidemiologists I've seen are around 1%, assuming that the healthcare system still functions, and much higher otherwise.
COVID-19's CFR & IFR might not even be the biggest problem. High rate of hospitalization and broken healthcare system, with all their ramifications, could be considered even worse.
There is no real consensus regarding IFR yet. I think the best data we have is from Diamond Princess, which is at least 10/712 or ~1.4% and may go up a bit from unresolved 15 serious/critical cases and 100 more active cases. The population there is older, but also have good care.
If the Diamond Princess age group represents just 20% of a population (they are not all elderly), population IFR must be >= 1.4%/5 = 0.28% and likely higher. 0.28% is above the IFR upper range from the paper in your comment.
“Estimated fatality ratio for infections 1%
Estimated CFR for travellers outside mainland China (mix severe & milder cases) 1%-5%
Estimated CFR for detected cases in Hubei (severe cases) 18%”
But the denominator in this formula strongly depends on who and how often you test. In other words: You don't know the number of cases.
Obviously, people who are severely affected are tested more often. People with mild or no symptoms might never be tested, even if they want to (I'm not sure about South Korea but for sure this is happening in Germany).
Based on people in the German parliament and the German soccer league, you can currently guestimate that 1% of the population is already infected (1% of the parliament and 1% of the premier league players are infected. I suspect that they are tested more often and even without symptoms. Maybe they have more contact to other people - maybe not).
Yes, this is a wild guess, but much better than taking the confirmed cases which are heavily biased towards people where the infection causes problems.