European Commission President Ursula von der Leyen told the New York Times on Sunday that tourists will need to have received both doses of a COVID-19 vaccine to travel to any of the 27 member states of the European Union. “All 27 member states will accept, unconditionally, all those who are vaccinated with vaccines that are approved by E.M.A. [European Medicines Agency],” von der Leyen said.

The three vaccines being deployed in the United States — Moderna, Pfizer, and Johnson & Johnson — have been approved by the E.M.A. European regulators also gave the go-ahead on the AstraZeneca vaccine, while the U.S. Food and Drug Administration is still reviewing it for approval.

The specifics of how American tourists will have to provide proof of vaccination are still being worked out. Officials in Brussels told the Times a “low-tech solution” will suffice as the United States and international governments work out the kinks of delivering a program “acceptable and readable in the European Union, and vice versa.”