ForwardKeys, which analyses 16 million flight reservations a day from major global reservation systems, also said that travel from the United States to and from the Middle East has been especially hard hit after President Donald Trump's move to ban people from seven Muslim-majority countries.
"Uncertainty reigns and the presidential rhetoric appears to be deterring visitors to the US," ForwardKeys founder Olivier Jager said in a statement.
US travel demand is set to be a topic at the world's largest travel fair, the ITB, in Berlin this week.
After the travel ban was imposed in January, international travel to the US dropped by 6.5 per cent in the following eight days, ForwardKeys data showed last month.
In its latest update on Monday, ForwardKeys said bookings to the United States recovered after the courts halted the ban, but dropped again in the nine days after plans for a new ban were announced on February 17.
The study also showed that accumulated US bookings to the Middle East were up by 12 per cent on last year in the three weeks before the ban. However, in the four weeks following the ban they were down 27 per cent.
Emirates and Qatar Airways, two of the Middle East's biggest airlines, declined to comment when asked about demand on US routes.
According to travel search site Kayak, searches from Europe for flights to the US are down by 12 per cent since the elections. However, Germans, some of the world's biggest spenders on travel, have not been deterred, with searches up 10 per cent in that period, Kayak said in data provided to Reuters.
Reporting by Victoria Bryan; additional reporting by Alexander Cornwell in Dubai; editing by Alexander Smith