The mandatory QT will be over from 04.01  if any of these conditions are met:

A Traveler – Fully Vaxxed + Booster  Traveler had 3 rounds of shots including the booster -100% Cleared and requires no quarantine, no time minimum or maximum on vaccine injection date. 

B Traveler – Full Vaxxed but NO Booster  Traveler already had the initial 2 shot dose  or (1 J&J dose) then that traveler’s vaccine record must indicate the 2nd shot was administered no more than 180 days in advance of arrival.

(C Traveler ) Recently Decided to Get Vaxxed  If traveler recently got vaxxed before traveling to Korea, the 2nd dose of Moderna, Pfizer, Sputnik, etc must be injected into traveler a minimum of  14 days before arrival in Korea

Furthermore, travelers must verify vaccination records BEFORE travel to Korea and get the QR Code before boarding the flight to Korea. You need your passport number and copies of the vaccination records. Contact the nearest South Korean Embassy for Updates.

Imagine Korea – Official Gov Travel News 

Pre-Flight Vaccine Record EntryQR-CODE