According to the latest information from the Korea Tourism Organization in Vietnam, from 12:00 AM on October 1st, 2022, travelers entering South Korea will no longer have to undergo PCR Covid-19 testing.
Starting October 1st, 2022, South Korea lifts Covid-19 testing requirement upon entry
According to the Korea Tourism Organization in Vietnam, South Korea has facilitated conditions for travelers with the latest regulations regarding Covid-19 control. South Korea has accepted multiple-entry visas, eliminated requirements for a specific number of vaccine doses, and expanded PCR testing areas at Incheon International Airport.

Efforts to change disease control policies have led to a significant increase in inbound tourists to South Korea since the beginning of the year. Previously, the country also abolished the requirement for Covid-19 testing before entry to make it more convenient for travelers to move around.
Recently on September 30th, 2022, South Korea officially announced the removal of PCR testing requirements one day after entry, effective from 12:00 AM on October 1st, 2022. Previously, the cost of PCR testing in South Korea was $80 per person, but recently reduced to $45 per person, alleviating concerns among travelers about additional testing fees.
Nowadays, regulations are no longer effective, barriers have been removed, and travel expenses have decreased, contributing to boosting tourism in South Korea. This year, South Korea expects to welcome approximately 150,000 Vietnamese visitors during the autumn-winter season.

With no PCR testing required upon entry, travelers to South Korea only need to fill out information on the Q-Code website and receive a code to complete the entry procedures. South Korea also does not require travelers to declare the number of Covid-19 vaccine doses they have received when providing information.
To facilitate the declaration of information on the system for Vietnamese guests, since August 22nd, 2022, South Korea has also deployed a Vietnamese version on the registration page for travelers to declare information easily, without language barriers.
According to Mytour
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Reference: Travel guide Mytour
TravelSavvy.comOctober 4, 2022