[tripletao]

The Korean number is the CFR (known deaths divided by known cases). The CDC number is the symptomatic IFR (all deaths divided by all symptomatic infected). These can't be directly compared--Korea has done a good job tracing and testing, but they're not claiming to be catching every case. In the other direction, Korea's number also includes asymptomatic cases while the CDC's doesn't.

Korea's average CFR over all population is ~2x even the high estimates of IFR from serology in high-incidence regions (New York, Lombardy) or universal PCR testing of isolated populations (Diamond Princess). It would make sense that their underascertainment would be yet higher for younger people, if they experience lighter symptoms and are thus less likely to seek medical care.