Passenger bookings for flights arriving in Paris during the Christmas period are down 13 percent on last year after the Nov. 13 terrorist attacks, with visits from the U.S, Spain, Japan and Germany worst affected, according to a study based on figures from 200,000 travel agencies.

While a 25 percent jump in cancellations the week after the tragedy has now eased, new bookings remain “dramatically below” last year’s level, travel-data specialist ForwardKeys said, citing reservation numbers through Nov. 20.

“The booking situation for arrivals during the Christmas holidays has become worrisome,” ForwardKeys Chief Executive Officer Olivier Jaeger said in an interview, citing figures for arrivals in the Dec. 25 to Dec. 31 period. “Paris will rebound. The question is, when will that start?”

France is the world’s biggest vacation destination, leaving it vulnerable to changes in consumer behavior. While Air France has said traffic immediately after the attacks remained in line with forecasts, past outrages have tended to produce a fall off in demand that recovers over weeks or months.

Cancellations were highest last weekend, according to ForwardKeys, with the second-most affected travel period being immediately prior to the start of United Nation climate talks in Paris on Nov. 30.

Ten days after the attacks that killed 130 people, European leaders are tightening border controls and meeting to seek a durable strategy for tackling Islamic State. The British Airline Pilots Association said separately that the expertise of air crew should be tapped to help assess safety risks.

“Terrorism is a risk that must be tackled and planes, passengers and crew must not be left in the firing line,” BALPA General Secretary Jim McAuslan said in a statement. “Pilots want to be engaged in discussions about security at both airline and governmental level.”

This article was written by Kari Lundgren from Bloomberg and was legally licensed through the NewsCred publisher network.

Photo Credit: A woman looks on at the first floor of the Eiffel Tower in Paris, Monday Nov. 23, 2015. Laurent Cipriani / Associated Press