With more COVID-19 vaccines getting approved, and more people being vaccinated. Airlines publically announce that they would only allow vaccinated passengers on board its flights.
The so-called ‘vaccination passports’ or ‘vaccination certificates’ now become must-have-document to travel.
https://www.vietnamimmigration.org/list-of-covid-19-vaccination-certificates-is-accept-to-apply-for-vietnam-visa/