here the answer to my questions by email from vietjet support on 29.10.21:
Dear Passenger,
Regarding your email, we would like to inform you that the Travel Measures for Entering to Phuket since 16 October 2021 are as follows:
All passengers must show the following documents to the airline at the check-in counter. (choose either one of the documents)
Must be fully vaccinated with an approved vaccine or have received 1 dose of Johnson&Johnson vaccine (no less than 14 days). (Combining vaccine formulas as prescribed by the Ministry of Public Health)
*As well as one who have recovered from COVID-19 for less than 90 days*
Negative Covid-19 certificate tested, with RT-PCR or ATK(Antigen Test Kit) test no longer than 7 days before departure.
House registration document (Home base in Phuket) or Hotel Confirm Reservation and receipt of hotel reservation must be shown at the check-in counter.
Register on website www.gophuket.com and present QR code before arrival.
Remark
For further information, please visit the website www.moicovid.com/ข้อมูลสำคัญ-จังหวัด/
The Travel Measures can change without prior notice, please recheck on the website www.moicovid.com before your departure date.
For the passenger traveling to Chiang Rai during the Covid-19 pandemic. CAAT allows the passenger from Domestic entering Mae Fah Luang Chiang Rai International Airport with qualified all conditions as below. (choose either one of the documents)
Passengers must show the Negative of Covid-19 test results within 72 hours before the flight departure (RT-PCR or Antigen Rapid test method or ATK negative test result from medical facilities ) upon check-in.
Fully vaccinated of Covid-19 vaccine (according to the requirements of each vaccine, except AstraZeneca can enter 14 days after the 1st injection).
Remark:
For passengers who comply with 1 and 2, the quarantine of 14 days can be exempted.
For further information about Covid-19 travel documents requirement, please visit the website www.moicovid.com/ข้อมูลสำคัญ-จังหวัด/
Best regards,
Kritsana P.
Contact Center Support Team
I think,the best is to ask some days before travelling directly at the airport of departure.
Robinsons