That, in turn, prompted countries to ban flights from Britain — a list that began with the Netherlands and Belgium and grew to encompass 17 European countries, as well as Canada, India, Russia, Jordan, and Hong Kong. The United States has not yet suspended flights, though Gov. Andrew M. Cuomo of New York was among those urging the Trump administration to do so, and he said he had secured the agreement of British Airways, Virgin Atlantic and Delta requiring a negative test result from passengers before departure to New York.
The European Union said it would develop a coordinated strategy for how to handle travel to and from Britain. But for now, its actions were uncoordinated, adding to the uncertainty at Heathrow, one of the main airports serving London, and other airports.
The variant has already been identified in small numbers in Denmark, the Netherlands and Australia, according to World Health Organization officials. The Italian health ministry reported on Sunday night that two people arriving in the country from Britain carried the strain.
British officials said they expected countries to ban travelers, since epidemiologists view that as necessary to break the chain of transmission across borders. But they appeared to be caught off guard by the French government’s decision to halt freight shipments, carried by truck drivers, for 48 hours.
France did not take such a step in March, when the virus first erupted in Europe, because the short crossing between the ports of Dover and Calais is a critical trade link for Britain and the continent, with thousands of trucks making the journey each day.
The restriction led to mile-long pileups on both sides of the channel, as hundreds of trucks laden with seafood and produce were stopped along the highway leading to the port of Dover. In Calais, on the French side, truckers waited for health guidance before driving their loads onto ferries to Britain. The lack of clarity left between 2,000 and 3,000 French truckers stranded on the British side.