In early 2023, I flew from the USA to Addis Ababa airport to Bangkok. I did not leave the terminal at Addis Ababa airport and the connection was a few hours, on one ticket. At BKK, the immigration officer immediately sent me to the health office to complete a form and upload a photo of my YF certificate, which I have. Don't know what happens if you don't have the yellow fever vaccination. I have a US passport.