Domestic visitors coming from 3 zones: Dark red, Red and Orange to Ko Samui are required to do a 14 days quarantine in Samui except having one of the three conditions below that quarantine will be no longer required:
Negative PCR test less than 72 hours.
Completed vaccination program (2 doses of Sinovac for more than 7 days or 1 dose of Astra Zeneca) for more than 21 days
In case of recovery from covid19 for not more than 90 days (need to show a medical certificate to authorities upon arrival)
Source: Official announcement of Surat Thani Province dated 24/06/21.