LONDON — Deborah Tudhope was growing anxious. An American lawyer living in London, she was hoping to fly back to the United States in two weeks to see her 96-year-old mother, who lives in a retirement home in Maine. But the Omicron-driven travel restrictions announced on Thursday by the White House have her worrying that the trip may not happen.
Ms. Tudhope, 72, has had to reschedule her required coronavirus test for the day before her flight, which the airline had already pushed back a day. With the rules seemingly shifting by the hour, she said she faced multiple hurdles: getting out of Britain, getting into the United States and visiting her mother in the home.
“I don’t know how this whole thing is going to work out,” said Ms. Tudhope, who described herself as disheartened, if not surprised, by the turmoil. “But I did make sure the flights are re-bookable.”
Such private dramas are playing out all over the world, as thousands of people — Americans living abroad and foreigners hoping to visit the United States — grapple with the new complexities of holiday travel in the age of Covid.
The spread of the Omicron variant in the last week has injected even more uncertainty into an already fraught exercise. On Thursday the Biden administration shortened the time frame for international travelers to the United States to take a Covid test within a day before departure, regardless of vaccination status.
That has left would-be travelers nervously calculating whether they will get test results back in time to make their flights or worrying that their home countries could impose more stringent travel bans while they are away.
The United States stopped short of imposing a mandatory seven-day quarantine on arrivals, which many travelers said would have torpedoed their plans. Nor did it upgrade its standard for an acceptable Covid screen from an antigen to a P.C.R. test, which can take significantly longer to produce results.
But the new one-day window for getting tested announced by the Centers for Disease Control and Prevention has nevertheless added an extra layer of preflight stress.
Paula Tolton, 23, an American student in Taipei, Taiwan, who plans to fly home next month to visit her family in Jacksonville, Fla., said she was worried that the new rules could cause her to miss her flight. Even the previous testing requirement for the United States, a negative result on a test within three days of arrival in the country, triggered “anxiety to the max,” she said.
“I’ve had that stress before when a P.C.R. test didn’t come back when I was supposed to fly in April,” she said. “I was freaking out.”
Public-health experts said there was a sound reason to shorten the time frame for test results: it would detect more infections in travelers. And since the results for antigen tests are normally available within a few hours, it should be possible to take a test and get the results within the prescribed period.
“A negative test is a good idea, especially since fully vaccinated people can transmit the virus,” said Devi Sridhar, head of the global public health program at the University of Edinburgh. But she acknowledged that the patchwork of travel restrictions and the shifting nature of the rules were exacting a toll on people.
“Uncertainty is killing the travel industry and people’s confidence in booking and traveling,” Professor Sridhar said. “They need a standard approach across countries and stability over time.”
Travel agents expressed relief that the Centers for Disease Control and Prevention did not recommend a seven-day quarantine. “You don’t go to New York to self-isolate in a nine-square-meter hotel room,” said Jean-Pierre Mas, president of Les Entreprises du Voyage, a union representing France’s major travel agencies and tour operators.
After more than a year of pandemic-related disruptions, Mr. Mas said many travelers were used to testing requirements and would probably not be put off by the new rules. But he said the lack of certainty — and a sense that governments were abruptly changing rules in reaction to the perceived threat of a new variant — was keeping people at home. After picking up over the summer and early fall, he said business had fallen over the past several weeks by about 25 percent, compared with the same period in 2019.
“For the United States, we’ve sold almost no trips over the past four to five days,” Mr. Mas said, even though it remains a popular destination for French tourists, who flock to New York City at Christmas.
What makes the latest turbulence especially painful for many is that it was only several weeks ago that the United States eased travel restrictions for international travelers who were fully vaccinated, leading to tearful reunions.
At the same time, travel between Europe and the United States had been on the rebound after a long hiatus during the earlier phases of the pandemic. Flights between the United States and Italy have been full until recent days, with bookings at almost the same level as in 2019, according to a spokeswoman for Fiavet, the association of Italian travel agents.
British Airways, Air France and United Airlines have added more trans-Atlantic flights, while ITA Airways, an Italian carrier, added a daily connection between Rome and John F. Kennedy International Airport in New York.
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Officials in Italy said the country was well-prepared to handle a surge in tests for passengers bound for the United States. In the weeks since the government began requiring frequent, negative tests for all unvaccinated Italian workers, pharmacies have processed up to one million rapid tests a day.
“The prospect of more rapid swabs for travelers to the U.S. is not a problem for pharmacies here,” said Marco Cossolo, president of Italy’s largest association of private pharmacies, Federfarma.
South Korea built up the capacity to administer an average of 68,000 P.C.R. tests a day in November, according to Seung-ho Choi, the deputy director of risk communication at the Korea Disease Control and Prevention Center. Results almost always come within 24 hours, he said, though travelers catching early-morning flights when clinics are closed might have to seek out hospitals that administer tests.
Britain is among several countries that have recently required tests for incoming travelers within a day or two after arriving. Randox Laboratories, a British company that provides Covid tests for travel, said on Thursday that since the changes were announced for travelers entering Britain last weekend, it had ramped up P.C.R. testing capacity to its pandemic peak of 180,000 tests per day.
That would also help with processing tests for travelers to the United States, the company said.
For Europeans with ties to the United States, the new rules are merely the latest wild card in a life already lived perpetually in flux.
“What a nightmare — enough!” said Alice Volpi, 28, when told of the impending American restrictions.
An Italian who was living in New York at the outset of the pandemic, Ms. Volpi recounted how she could not return home to Italy for several months because of her country’s travel ban. When she finally got home, a travel ban imposed by the United States prevented her from returning to see her boyfriend in New York.
“The most frustrating part is that you can never make a plan more than one week in advance because everything can change every day,” said Ms. Volpi, who insisted she would press on with plans to visit her boyfriend at Christmas. “That doesn’t allow me to be serene.”
For some Americans living abroad who fear that borders may close again if Omicron proves to be a lethal threat, the solution is to move up their travel timelines. The testing requirements are stressful, they said, but not as much as the possibility that the Biden administration might eventually cut off travel pathways completely.
“That’s what I’m most worried about — not getting to see my family,” said Sarah Little, 25, who moved from New York to London in September to study. She had originally planned to fly home closer to Christmas, but is now trying to book a flight early next week.
“It would just be devastating if I couldn’t get home,” Ms. Little said.
Gaia Pianigiani and Emma Bubola contributed reporting from Rome; Saskia Solomon and Isabella Kwai from London; Aurelien Breeden from Paris; John Yoon from Seoul and Sheryl Gay Stolberg from Washington.