[summerlight]

Vaccine efficacy on the Delta variant is still a debatable topic, and it's dangerous to make any conclusion from a single reference limited to a very specific, narrow subset of sample.

You probably remember Israel's report (which is strongly motivated to promote booster shots) indicated that vaccine's efficacy was pretty low, but it turns out to be a textbook case of Simpson's paradox[1] from extremely biased vaccination rate.

From what I saw from KDCA's daily reports (which performs extensive contact tracing with a pretty high coverage, not even remotely comparable to the US), it's more of 70% protection against Delta. Though it's possible that its efficacy is waning over time, which may explain the gap between Korea and Israel.

[1] https://www.covid-datascience.com/post/israeli-data-how-can-...