The window to find dirt-cheap fares to Europe is closing.

The Biden administration on Monday said the U.S. in November will start allowing in vaccinated foreigners from 33 countries, including the U.K., China and EU nations, easing rules set early in the pandemic.

That’s great news for airlines that are desperate to drum up revenue after a historic lull in demand for routes that were among the most popular before the Covid-19 pandemic. Many EU countries have been welcoming U.S. tourists for months since vaccinations became widely available, but that was not reciprocated by the United States.

“In the past, as restrictions have been eased, there has been an increase in bookings for travel, and we expect a similar reaction here,” Conor Cunningham, executive director of MKM Partners, wrote in a research note to investors.

Bargain hunters eager to take advantage of the relatively cheap flights might be out of luck as demand for trans-Atlantic travel rises.

Round-trip flights to Europe, including the U.K., from the U.S. are going for about $565, a level not seen in its roughly five years of collecting data, said fare-tracking company Hopper.

Fares had dropped 15% from Aug. 30, after the European Union recommended that its member countries reinstate travel restrictions on the U.S. The advisory was nonbinding, however, and U.S. travelers can still visit a host of countries if they meet requirements like proof of Covid-19 vaccination or a recent negative Covid test, if not a combination of both.

Adit Damodaran, economist at Hopper, said he expects airfares to rise from Europe to the U.S. on the lifted travel restrictions and from the U.S. to Europe as more travelers realize the EU notice “was a soft advisory.”

Airlines didn’t immediately say whether they would add flights following the loosened U.S. travel rules, but carriers pounced with added service to destinations like Iceland, Croatia and Greece when those countries started allowing U.S. visitors in earlier this year.