As of midnight of March 22 2020:
1. All foreigners arriving to Thailand must present a medical certificate stating they pose no risk of being infected with Covid-19, issued to them within the past 3 days as well as travel insurance covering at least USD100,000 and includes Covid-19.
2. All Thai citizens arriving back to Thailand must present a fit to fly health certificate and a travel certificate issued to them by the Thai Embassy/Consulate. All passengers must also complete the T.8 form. This can also be completed via. the AOT Airports application. https://www.airportthai.co.th/