LONDON — Dozens of new cases of the Omicron variant were reported in Britain and Denmark on Sunday, adding to increases across Europe and fueling fears that the virus has already spread widely.
The coronavirus variant has spread to at least 45 nations worldwide, with the United States and much of Europe reporting a number of new cases in recent days. And while much uncertainty remains about what impact the Omicron variant will have on the pandemic, many nations have scrambled to impose travel restrictions — or in some cases introduced more serious measures.
With cases of Omicron now growing worldwide, the prospects of even more stringent restrictions are looming over a holiday period that many had hoped would be a return to some normalcy. In Europe, already the epicenter of a surge in the pandemic in recent weeks, the uncertainties raised by Omicron have ignited fears that the winter ahead will be more difficult than anticipated.
On Sunday, Britain’s health security agency confirmed 86 additional cases of the Omicron variant, bringing the total nationally to 246, while authorities in Denmark reported 183 cases of the variant. Both nations are widely seen as leaders in genomic sequencing and testing, giving them an edge in tracking the spread of the virus and its mutations.
That the number of Omicron cases is rising quickly was clear. What it might mean was less so.
“We’re going to see lots of big numbers over the course of the next several weeks in countries around the world,” said Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. “And this shouldn’t be a surprise. This virus is just acting like a highly transmissible respiratory virus.”
Part of the increase may be explained by the new laser focus of public health officials on the variant, which early evidence suggests may spread more quicklythan the Delta variant.
“Once you find someone who is infected,” Dr. Osterholm said, “and you start looking at their contacts or the environment they’re in, you’re just going to find a lot more.”
Dr. Peter J. Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine, said that the known numbers were so small that it was hard to know how much to make of the increase. A few hundred cases is still a “tiny fraction” of around 44,000 new coronavirus cases on average that Britain experiences daily, he said.
“I think the question people want to know is whether Omicron is going to outcompete Delta, and it’s a possibility,” he said.
At the moment, Dr. Hotez said, there is not enough data to conclude that. If at the end of next week Omicron represents “even 10 percent of the Delta cases, then I’ll be more concerned,” he said.
But even before the discovery of the new variant, some public health experts were raising the alarm that the travel restrictions in place in much of Europe were not enough to stem the surge in coronavirus cases already taking place.
Some lamented what they said was the cost of nations letting their guard down, criticizing the failure to reimpose restrictions like indoor mask wearing and social distancing, and to remind people to isolate if they have been exposed to the virus.
Jeremy Farrar, the director of the Wellcome Trust and a former member of the British government’s scientific advisory body, wrote in The Observer that the rise of Omicron was a signal that the “staggering progress” made since the start of the pandemic “is being squandered.” Richer nations, he argued, had a “blinkered” focus and were “lulled into thinking that the worst of the pandemic was behind us.”
“This variant reminds us all that we remain closer to the start of the pandemic than the end,” he said.
In parts of the United States, health officials have also seen a steady climb in the number of Omicron cases. The variant has been detected in at least 16 states: California, Colorado, Connecticut, Hawaii, Louisiana, Maryland, Massachusetts, Minnesota, Missouri, Nebraska, New Jersey, New York, Pennsylvania, Utah, Washington and Wisconsin.
Some Americans, too, are becoming more nervous.
“We’re paying closer attention, which we haven’t probably for a little while,” said Rory Bakke, who lives in Marin County, Calif. “It’s upped our attentiveness to the reports of symptoms and how contagious it is and the science reports.”
Ms. Bakke expressed frustration over the latest threat.
“I feel like if everyone had just followed the guidelines, we wouldn’t be in this situation,” she said. “So that’s disheartening.”
The Omicron variant was first identified in southern Africa in late November. On Saturday, Zambia became the latest African country — alongside South Africa, Botswana, Nigeria and Ghana — to report cases.
Since its emergence, a number of travel restrictions have been imposed to try to slow its spread, including in the United States and Europe.
Still, some European governments have been hesitant to impose sweeping new domestic restrictions ahead of a highly anticipated period of travel and big gatherings, especially given the lockdown in much of Europe last winter. Many have instead opted to focus on restricting travel from abroad or requiring more testing for travelers.
But some fear the travel restrictions are a case of too little too late.
“I think that might be a case of shutting the stable door after the horse has bolted,” Mark Woolhouse, a professor of infectious disease epidemiology at the University of Edinburgh who advises the government, told the BBC.
He said it was “too late to make a material difference to the course of the Omicron wave.”
So far, the British government has told the public to proceed as usual with their holiday plans, though it has urged people to get booster shots. Dominic Raab, Britain’s deputy prime minister, called that the “surest defense” in a BBC interview on Sunday.
“Our message is this: Enjoy Christmas this year,” he said. “The vaccine rollout means we’re in a position to do so.”
In Denmark, health authorities announced on Sunday that 183 people had confirmed cases of the Omicron variant, a “worrying increase,” said Henrik Ullum, head of the Statens Serum Institut, Denmark’s public health agency.
“There are now ongoing infection chains,” he said in a statement, where the infection is seen among people who have not been traveling or had connections with travelers.
European countries have taken steps to curb social contacts in recent days amid an overall surge in cases.
Belgium is requiring people to work from home and ordered schools closed a week earlier for Christmas; Italy banned unvaccinated people from certain leisure activities; and Ireland has shuttered night clubs and restricted gatherings.
Germany has banned the unvaccinated from much of public life. And in an indication of the severity of the situation, the German government, which had been hesitant to put in place government mandates around the pandemic because of the country’s history with authoritarianism, has plans to make vaccination compulsory next year.
Some nations have already seen pushback to the restrictions. In Austria, tens of thousands marched in protest on Saturday for the second weekend in a row over the government’s decision to impose a tough new lockdown and its plans for a vaccine mandate.
Experts had time and again have warned that not enough had been done to combat the Delta variant across Europe. This week, they reiterated those warnings and call for action.
Michael Ryan, the head of the emergencies program at the World Health Organization, speaking last week at a news conference, said European countries should have taken more precautions this autumn to protect their populations.
“We will have to be a little patient in order to understand the implications of the Omicron variant,” he said, “but, certainly we are dealing with a crisis now. And that crisis is in Europe, and it is being driven by the Delta variant.”
Now, he said, it is time for “everyone to recommit ourselves to controlling the pandemic of multiple strains or multiple variants of the same virus.”
Emily Anthes contributed reporting from New York, Thomas Erdbrink from Amsterdam, Jasmina Nielsen from Copenhagen and Holly Secon from California.