Covid Live Updates: Biden to Announce New Virus Plan as Omicron Reaches U.S.

President Biden, confronting a worrisome new coronavirus variant and the potential of a winter surge, will lay out a new pandemic strategy on Thursday afternoon that includes hundreds of vaccination sites aimed at families, booster shots for all adults, insurance reimbursement for at-home coronavirus tests and fresh travel restrictions, including a requirement that international travelers must show proof of a negative coronavirus test taken within a day before departing for the United States.

Mr. Biden plans to announce the strategy at the National Institutes of Health. It comes a day after the new Omicron variant was detected in the United States for the first time, in California.

Senior administration officials, speaking on condition of anonymity to preview the plan, said it was aimed at keeping the economy, workplaces and schools open.

A big part of the plan is a renewed push to get people vaccinated, including the latest group to become eligible, children ages 5 to 11. The administration plans to launch “hundreds of family vaccination clinics” that will offer vaccinations and boosters for people of all eligible ages, according to a fact sheet provided by the White House.

The president will also announce a national campaign to reach the 100 million Americans who are eligible for booster shots and have not had them. The campaign will include paid advertising and free rides to vaccination sites coordinated by AARP, the advocacy group for older Americans. And the Federal Emergency Management Agency will launch what the administration is calling Family Mobile Vaccination Clinics, beginning with deployments to Washington and New Mexico. The goal is for states and localities to replicate the model “with full federal funding and support,” officials said.

Mr. Biden will call on employers to provide paid time off for employees to get boosters.

Mr. Biden ran for office in 2020 on a promise to get the pandemic under control. Since then, though, the virus “has thrown us a number of curveballs, and unfortunately they were thrown at 200 miles an hour,” said Michael T. Osterholm, who directs the Center for Infectious Disease Research and Policy at the University of Minnesota.

Many experts predict a surge in the United States over the winter, regardless of whether the Omicron variant spreads widely in the country. The nation has been reporting an average of more than 80,000 new cases a day over the last few weeks, according to a New York Times database; six months ago, the average was roughly 12,000 new cases a day.

The Biden administration’s pandemic response has relied heavily on vaccinations — too heavily, in the view of some experts, who have argued for months that testing and mask-wearing are also essential to containing the virus, and will become even more so if the Omicron variant is found to evade protection from vaccines.

The variant was first spotted by scientists in southern Africa and is now known to be present in more than 30 countries including the United States. It has mutations that scientists say may allow it to spread more quickly and cause more breakthrough infections in vaccinated or previously infected people, though neither characteristic has yet been confirmed.

In the United States, home coronavirus tests have been relatively hard to come by because of supply shortages, and they are expensive — as much as $25 apiece. Dr. Carlos del Rio, an infectious disease specialist at Emory University, said that rather than have people go through the cumbersome process of seeking insurance reimbursement for tests, “we should just subsidize them and make it incredibly cheap.”

In Britain, he noted, rapid tests are free, and in Germany they cost consumers about $1 apiece.

Reimbursement for at-home tests in the United States will not happen immediately, and will not be retroactive, the senior administration officials said, adding that federal agencies would issue guidance by Jan. 15 to clarify that insurers would have to reimburse people for at-home tests during the Covid-19 public health emergency. It was unclear how many tests a person could be reimbursed for buying.

Private insurers already cover the cost of coronavirus tests administered in doctor’s offices and other medical facilities. At least eight at-home tests are on the U.S. market.

Looking forward, experts envision a world where people will test themselves as soon as they exhibit symptoms — and then, if they are positive, would go into quarantine and seek treatment with new antiviral medicines that are in development. The White House says it is taking steps to secure 13 million courses of antiviral treatments.

Mr. Biden’s new strategy will extend the current mask mandate for people on airplanes, trains and buses, and in terminals and transit hubs, through mid-March.

Only six states now require people to wear masks in indoor public settings regardless of their vaccination status. Three more — California, New York and Connecticut — require masks indoors for people who are unvaccinated.

Top German officials said on Thursday they had agreed on tough new coronavirus restrictions that would leave unvaccinated people out of many aspects of public life, as the country tries to fight a monthlong surge in infections that has been breaking daily case records.

“You can see from the decisions that we have understood that the situation is very serious,” Chancellor Angela Merkel told reporters at a news conference after her teleconference meeting with state governors.

Under the new set of rules, those wishing to shop anywhere but in stores carrying basic necessities will have to present proof of full vaccination or documentation of recovery. States may also add the requirement that a negative test result be presented on top of the other documentation. Where they were not doing so already, restaurants, bars, museums and theaters will also bar entry to those who are not vaccinated or recovered.

In addition, for those who cannot provide proof, meetings, whether at home or in a public space, will be limited to two households.

The restrictions stop short of obliging the unvaccinated to stay at home, as restrictions enacted by Austria last month did.

In what is likely to be Ms. Merkel’s last meeting with governors, states agreed to pass the new rules in the coming days. Olaf Scholz, who is expected to be sworn in next week as new chancellor, was active in the talks.

On Thursday, he reiterated his promise to oversee distribution of an additional 30 million doses of vaccine by Christmas, for which a task force headed by a military general was constituted. Mr. Scholz also spoke about passing a mandatory vaccination law that could go into effect in winter, something he had first discussed publicly on Tuesday.

In virus hot spots — districts where more than 350 infections are registered per 100,000 in a week — bars and nightclubs would be forced to close and indoor gatherings would be limited to 50 participants.

Like last year, selling firecrackers will be prohibited at the end of December, in an attempt to discourage crowded New Year parties.

German health authorities registered 73,209 new reported cases on Wednesday and 388 new deaths.

Minnesota health officials said on Thursday that a man who lives in the state was infected with the Omicron variant of the coronavirus. The man, who officials said had recently traveled to New York City, represents the second known case of the variant in the United States.

Leaders in Minnesota said the discovery was unsurprising, and credited robust disease surveillance systems for finding it.

“This news is concerning, but it is not a surprise,” Gov. Tim Walz said in a statement. “We know that this virus is highly infectious and moves quickly throughout the world. Minnesotans know what to do to keep each other safe now — get the vaccine, get tested, wear a mask indoors, and get a booster.”

Much remains unknown about Omicron, including whether it is more transmissible and capable of causing more serious illness. There is some evidence the variant can reinfect people more readily.

According to the Minnesota Department of Health, the man is a resident of Hennepin County, which includes Minneapolis. He had been vaccinated and is no longer feeling symptoms, the department said.

The man first developed mild symptoms on Nov. 22, shortly after traveling to New York City for the Anime NYC 2021 convention at the Javits Center, the department said. The announcement did not indicate whether the man had traveled anywhere else recently.

He was tested for the virus on Nov. 24. The state’s Public Health Laboratory determined that he had the Omicron variant. Minnesota officials said they were working with New York City and federal health officials to look into the case, and that the man has spoken with case investigators.

On Wednesday, California health officials announced that a San Francisco resident had been infected with the Omicron variant — a finding they emphasized was inevitable, as they worked to contain alarm over the variant’s discovery in the United States.

Experts have said since the Omicron variant was first identified that it was only a matter of time before the variant made its way to the United States, and that once a case was detected, many more would probably soon be found.

“I’m personally surprised it took this long” for the first case to appear, Dr. Bob Wachter, a professor and chair of the department of medicine at the University of California, San Francisco, said on Wednesday. “Today it’s in California, tomorrow it’ll be several other states.”

Gov. Kathy Hochul of New York said on Thursday that everyone who attended a recent anime convention in Manhattan should get tested for the coronavirus, after an individual who tested positive for the Omicron variant in Minnesota recently traveled to to the conference.

Ms. Hochul said the individual, a Minnesota resident who was vaccinated and suffered mild symptoms, had attended the Anime NYC 2021 convention at the Javits Center in Midtown Manhattan. She urged people who attended Javits from Nov. 18 to Nov. 22 to get tested and said that health officials would be in contact with attendees.

“We do anticipate they’ll be more cases,” Ms. Hochul said. “This is not cause for alarm; it was foreseen ever since it was first reported out of South Africa, that we knew it would come to New York State at some point.”

Much remains unknown about Omicron, including whether it is more transmissible and capable of causing more serious illness. People had to be vaccinated with at least one dose and wear masks to attend the conference. Proof of at least one dose is required for many indoor activities citywide. New York State and New York City do not have universal indoor mask mandates.

The Omicron variant still had not been identified in New York, Ms. Hochul said, adding that New Yorkers should continue to wear masks and get tested, while unveiling a new public messaging campaign to encourage people to get booster shots.

Last week, Ms. Hochul declared a state of emergency to give the state more flexibility to respond to the rise in cases and staff shortages in health care facilities. Under an executive order that goes into effect on Friday, for example, hospitals that have less than 10 percent bed capacity will have to temporarily pause elective surgeries.

Ms. Hochul’s made her remarks on Thursday during a coronavirus briefing in which she introduced Dr. Mary T. Bassett, the newly-appointed New York State health commissioner.

Dr. Bassett steps into the role as parts of upstate New York grapple with a spike in coronavirus cases, while the state contends with the largely unknown Omicron variant during the cold winter months, when people are likelier to gather indoors and travel during the holidays.

“The fact that we have not detected it may mean that it’s still extraordinarily rare here, that it is the proverbial needle in the haystack,” Dr. Bassett said of the Omicron variant. “We now have an exposure and we fully expect that it will be detected in the coming days.”

Dr. Bassett, who ran New York City’s health department for four years until 2018, took the helm of an embattled Health Department that suffered from an exodus of health officials under former Gov. Andrew M. Cuomo, who repeatedly interfered in the department’s coronavirus response.

Dr. Bassett replaced Dr. Howard A. Zucker, who announced his resignation in September following political pressure over his role in potentially helping obscure the coronavirus death toll in nursing homes under Mr. Cuomo. Appointed by Ms. Hochul, who replaced Mr. Cuomo after he resigned in August, Dr. Bassett faces the daunting task of restoring trust in the state’s public health apparatus among experts and New Yorkers alike.

Dr. Bassett won acclaim when she was the city’s health commissioner for her role in navigating the Ebola scare in 2014, as well as an outbreak of Legionnaire’s disease and the threat of Zika. She most recently served as director of Harvard’s FXB Center for Health and Human Rights.

The French authorities confirmed the first cases of the Omicron version of the coronavirus in mainland France on Thursday, but their alarm remained focused on a surge of infections fueled by the Delta variant.

France reported nearly 50,000 new cases of the virus in 24 hours on Wednesday, the highest daily total since the spring. The number of reported cases per 100,000 people has soared from less than 100 to more than 300 over the past month.

“We need to anticipate — there are still a lot of uncertainties,” Jean-François Delfraissy, the head of the French government’s Covid-19 scientific advisory council, told BFMTV on Thursday, referring to Omicron. “But let’s not fight the wrong fight. The real fight, the real enemy, is the fifth wave with the Delta variant.”

The surge has alarmed French authorities, even though they have so far ruled out a return to lockdowns or business closures. Mr. Delfraissy said that cold had pushed people indoors and that social distancing was no longer being scrupulously followed. The average number of new hospital admissions, including in intensive care, have also increased by roughly 40 percent over the past weeks, according to official statistics.

But hospitalizations are still below the peaks seen in previous waves, thanks to a vaccination rate of 75 percent of the entire population, and Mr. Delfraissy said that if people exercised renewed vigilance — by avoiding gatherings, working from home when possible and wearing masks more often — France could be spared the worst outcomes.

“Christmas isn’t in danger if we are all careful,” he said.

The French government, which recently made all adults eligible for booster shots, has steered clear of mandating vaccines, arguing that coercion would be counterproductive. Olivier Véran, the health minister, told reporters this week that a more “powerful incentive” was the national health pass, which is required to access museums, restaurants, cinemas and other public venues.

The announcement of two Omicron cases on Thursday in mainland France has added to concerns, even though scientists are still trying to understand the threat posed by the variant.

The health authority for the Île-de-France region, which includes Paris, said that the Omicron variant had been found in a man in his 50s, who returned from Nigeria last week and tested positive for Covid-19 after disembarking from his flight, though he showed no symptoms. The man, who was not vaccinated, was isolating at home, officials said.

In eastern France, health authorities in the Grand-Est region said in a statement that Omicron had been detected in a woman in her 40s who returned from South Africa last week. The woman was vaccinated but experiencing symptoms, and has been isolating at home.

Previously, France had confirmed only one case of the Omicron variant, in the overseas department of Réunion, in the Indian Ocean.

Uncertainty over how dangerous Omicron really is had prompted the French authorities to halt flights with 10 countries in southern Africa, where the variant was first detected. Flights will be allowed to resume starting this weekend, but with some restrictions on travelers still in place. France will also require all visitors arriving from outside the European Union to provide a negative coronavirus test result, regardless of their vaccination status.

As officials scrambled to contain alarm over the detection of a case of the Omicron variant in California, state leaders portrayed the finding as an encouraging — and inevitable — result of the state’s efforts to be prepared.

“This was predictable,” said Gov. Gavin Newsom, speaking at a news conference on Wednesday in the Central Valley, where he encouraged residents to get vaccinated and get booster shots. “And it was not surprising that the state of California detected it.”

State health officials said the discovery of the Omicron variant — in a traveler who returned to California from South Africa on Nov. 22 — would prompt increased Covid-19 testing at California airports, focusing on arrivals from countries identified by the Centers for Disease Control and Prevention as potential sources of the variant.

However, Mr. Newsom — who beat back a recall effort in September that was fueled in part by resistance to the state’s pandemic health restrictions — suggested that for now at least, the state would not tighten public health rules or close schools.

Mr. Newsom said there were “no indications” that such restrictions would be needed “as long as we continue our nation-leading efforts.

State officials had said it would be only a matter of time until the Omicron variant appeared on the West Coast. California is a first U.S. stop or a destination for millions of global travelers, and as recently as Sunday, the state’s Department of Public Health had said that officials were monitoring for signs that the variant had arrived.

Mr. Newsom said the infected patient — a fully vaccinated resident of San Francisco between the ages of 18 and 49 — had been tested after traveling to South Africa, the region where the variant was first detected.

The patient, he said, had landed in California on Nov. 22, developed Covid-19 symptoms three days later and was tested on Nov. 28. The variant was confirmed by scientists at the University of California, San Francisco, the next day.

San Francisco public health officials said the individual was self-isolating, experiencing mild symptoms and assisting with contact tracing. The person had received two doses of the Moderna vaccine but was within the six-month window and had thus not received a booster, Mr. Newsom said.

The governor said the state has partnered with top scientists at the University of California, San Francisco, to sequence Covid-19 cases, built up testing and succeeded in vaccinating many of its residents.

Dr. Mark Ghaly, the state’s secretary of health and human services, went so far as to say that Californians were “proud” to have identified the Omicron case.

Almost 80 percent of California residents have gotten at least one dose of the vaccine, after months of campaigning by state officials. Cases and hospitalizations have been inching mostly downward since a summer rise driven by the Delta variant — though hospitals in areas like the Central Valley, where fewer residents are vaccinated, have filled.

In San Francisco, officials sought to reassure residents.

“San Francisco has one of the highest vaccination rates and lowest death rates in the country because of the actions our residents have taken from the beginning of this pandemic to keep each other safe,” Mayor London N. Breed said in a statement. “We knew that it was only a matter of time until the Omicron variant was detected in our city, and the work that we have done to this point has prepared us to handle this variant.”

In the Bay Area, longstanding mask mandates — some of the state’s most enduring restrictions — have recently been relaxed as the spread of the virus has slowed. Local governments in the Bay Area and in other parts of the state have begun to require businesses to verify vaccination status for entry, and more workers have been required to get their shots — a trend that officials have credited with helping to curtail the transmission of Covid.

Scientists in the United States and Britain believe they may have identified a key step in how the Covid vaccine developed by AstraZeneca and Oxford University may cause an extremely rare but serious blood-clotting disorder.

The AstraZeneca vaccine was expected to be the workhorse of the world’s vaccination efforts, thanks in part to pledges to manufacture it on a nonprofit basis during the pandemic and to make it available cheaply in poorer countries. The company and its partners have distributed more than two billion doses worldwide.

But reports of the rare side effect — an autoimmune response that has led to dangerous and sometimes fatal clotting in a small number of cases — were among a series of setbacks that tarnished the shot’s reputation and caused many European countries to limit its use. It has yet to receive authorization in the United States, although the company has said that it hopes to achieve approval soon.

“We hope our findings can be used to better understand the rare side effects of these new vaccines — and potentially to design new and improved vaccines to turn the tide on this global pandemic,” Prof. Alan Parker of Cardiff University’s School of Medicine, one of the researchers involved in the study, said in a news release.

The findings, which were published on Thursday, in the journal Science Advances. suggest that the problem is linked to the vaccine’s use of another, harmless virus — an adenovirus — to deliver a coronavirus gene into human cells, in order to train the immune system to recognize and battle the virus.

The shot is injected into muscle tissue, but the report suggests that if the adenovirus leaks into the bloodstream it can bind to a protein in the blood called platelet factor 4, or PF4, which is involved in the natural clotting process.That process, in turn, could lead to the release of antibodies against the protein, causing platelets to cluster and blood clots to form in very rare cases, the authors of the article said.

“With a better understanding of the mechanism by which PF4 and adenoviruses interact there is an opportunity to engineer the capsid, or outer shell of the vaccine, to prevent this interaction occurring,” Dr. Parker said.

The Johnson & Johnson vaccine also uses an adenovirus, and has also been linked to the rare blood clotting disorder. The Pfizer or Moderna shots are based on a different technology, one that does not involve a helper virus.

Concerns about the rare side effect first emerged in March, causing many European nations began to rethink the vaccine’s use in some age groups.

The reaction was first discovered by scientists in Germany and Norway, but how or why it took place had remained a mystery.

Public health experts have expressed concern that the rare vaccine-related reactions have fueled hesitancy, particularly in Europe, and continue to emphasize that the AstraZeneca vaccine’s benefits far outweigh the risks.

In Britain, where the vaccine first went into use in January, the National Health Service reports that “the risk of this extremely rare side effect is around 1 in every 100,000 first doses” whereas the benefit of one dose leads to an 80 percent reduction in deaths. As of Aug. 11, the side effect had been linked to 73 deaths in Britain, according to the country’s Medicines and Healthcare Products Regulatory Agency. Britain has given more than 25 million first doses of the vaccine.

When the United Nations made its last appeal for humanitarian aid funding before the pandemic, it asked donors for about $29 billion. But in the past year alone, there has been a huge jump in the number of people needing help. And so the United Nations is asking for more aid — $41 billion.

As the pandemic enters a third year, and the toll of conflicts and climate change rise, the United Nations said on Thursday that it needed to help 183 million people in 63 countries who are suffering the consequences. That compared with 100 million people at the time of the last appeal, in 2019.

More than 1 percent of the world’s population are now displaced by conflicts and disasters, Martin Griffiths, the United Nations emergency relief coordinator, told reporters in Geneva in announcing the organization’s 2022 funding drive. About 45 million people now face famine, some as a result of climate change.

The pandemic has already forced 20 million people into extreme poverty, he said, citing World Bank estimates, and the new Omicron variant would further ratchet up the economic damage. “With Covid continuing to threaten us and continuing to mutate, we will continue to see increased humanitarian needs,” he said.

South Koreans who went overseas to travel or live abroad and were expecting to come back home without having to quarantine got an unpleasant surprise after the government announced exemptions would be halted for visitors from all countries, including fully vaccinated Korean nationals.

The new regulations threw a wrench in Christmas plans for many of these travelers, who will have to self-isolate over the holidays. Previously, such travelers who had been fully vaccinated for at least two weeks were exempted from quarantine.

South Korean officials announced the change in quarantine rules on Thursday, after the country’s first cases of the new Omicron variant were confirmed the night before. The 10-day quarantine requirement for all arrivals takes effect on Friday and will continue until at least Dec. 16.

The measures were aimed at forestalling community spread of Omicron, Jeong Eun-kyeong, the commissioner of the Korea Disease Control and Prevention Agency, told a news conference on Thursday. “We must strengthen measures for inbound travelers,” she said.

On Thursday the nation reported its record number of daily cases at 5,266. This is its worst wave of cases despite a vaccination rate of 79 percent, according to figures collated by the Our World in Data project at the University of Oxford. South Korea is also one of the nations that have barred arrivals from several African countries in response to South Africa’s initial detection of the Omicron variant.

Some South Koreans said they were confused and frustrated by the sudden change in regulations.

“This isn’t fair,” said Alisha Kim, a mother of two sons in college in the United States, who was about to return to Seoul. She said that she would not have made the trip to visit them had she known she would be required to quarantine when she returned.

“We all worked so hard to abide by the government regulations until now, and wore our masks and washed our hands, and now all of a sudden we have to quarantine,” she said.

South Korea introduced a “living with Covid” plan this month, easing some social distancing measures and limits on business operating hours. It will delay any further loosening of restrictions for at least four weeks.

New York City went from being an epicenter of the coronavirus outbreak early in the pandemic to now having a higher percentage of vaccinated residents than the national average. Today, the city is bracing for the arrival of the Omicron variant, which was just detected in California.

“We do anticipate detecting Omicron in New York in the coming days,” the city’s health commissioner, Dr. Dave Chokshi, said on Monday.

Three variants have already been detected in New York City so far this year — Iota, Alpha and Delta. Each new variant provoked worry, but ultimately, proved less devastating than anticipated, thanks, in part, to New York’s relatively high rate of vaccination. About 77 percent of residents have received at least one shot.

Considerable levels of natural immunity from the devastation of the first wave in spring 2020, widespread mask-wearing and robust testing were also factors.

“I think we are potentially more prepared than most,” said Dr. Bernard Camins, an infectious diseases specialist and medical director of infection prevention for the Mount Sinai Health System. “The question is whether at this point people are more fatigued from all those mitigation strategies, and they may not listen.”

New York City’s approach has been to focus on vaccines and boosters.

When asked by a reporter on Monday why he was recommending, rather than mandating, mask-wearing until more is known about Omicron, the mayor said, “What we do not want to do is mix messages about what’s the thing that actually has the most profound impact.”

He added: “The thing that we need to do with urgency is get people vaccinated.”

First identified in Botswana and South Africa, this new iteration of the coronavirus has prompted concern among scientists and public health officials because of an unusually high number of mutations that have the potential to make the virus more transmissible and less susceptible to existing vaccines.

Here is a look at what we know — and don’t — about the variant:

What is Omicron?

The World Health Organization has called Omicron a “variant of concern” and on Monday warned that the global risks posed by it were “very high,” despite what officials described as a multitude of uncertainties. Cases have been identified in 20 countries so far, including Britain, Italy, Belgium and the Netherlands. Although Omicron has not yet been detected in the United States, experts say it is only a matter of time before the variant shows up.

Should we be worried?

Omicron’s discovery has prompted considerable panic across the globe, with a number of countries banning flights from southern Africa, or — like Israel, Japan and Morocco — barring entry of foreign travelers altogether.

But public health experts have urged caution, noting that there is as yet no firm evidence that Omicron is more dangerous than previous variants like Delta, which quickly overtook its predecessors in the United States and other countries.

Much remains unknown about Omicron, including whether it is more transmissible and capable of causing more serious illness. There is some evidence the variant can reinfect people more readily.

There are early signs that Omicron may cause only mild illness. But that observation was based mainly on South Africa’s cases among young people, who are less likely overall to become severely ill from Covid.

Do vaccines protect against Omicron?

Scientists expect to learn much more in the coming weeks. At the moment, they say there is no reason to believe Omicron is impervious to existing vaccines, although they may turn out to be less protective to some unknown degree.

There’s another reason to remain calm: Vaccine makers have expressed confidence they can tweak existing formulations to make the shots more effective against new variants.

Also reassuring: Omicron’s distinctive mutations make it easy to quickly identify with a nasal swab and lab test.

Elad Maor initially feared that he might have exposed hundreds of people to the virus when he became the first Israeli to test positive for the new Omicron variant on Saturday morning.

In the three days before his positive results, Dr. Maor, a cardiologist, had attended a large staff meeting at his hospital east of Tel Aviv. He had inserted stents into the arteries of 10 patients. And he had driven to a cardiology conference north of Tel Aviv, sharing the 90-minute car journey with a 70-year-old colleague, and lunched there with five others in a crowded canteen.

Dr. Maor, 45, had attended a piano recital with dozens in the audience, where his 13-year-old played a short piece by Stephen Heller, a Hungarian composer. And finally, last Friday night, Dr. Maor had eaten sea bass at the home of his in-laws, together with his wife and nine other family members.

But of these many people, most of whom had received three shots of the Pfizer-BioNTech vaccine, only his 70-year-old colleague has so far tested positive for the Omicron variant in the five days since.

That number may yet rise, as the virus can take several days to show up in tests, and not every contact has been tested. But at least 50 people have already been screened with a P.C.R. test by Dr. Maor’s hospital, the Sheba Medical Center, and at least 10 of those have been tested at least three times.

These initial results have led the infectious disease experts at Sheba, which houses one of Israel’s leading coronavirus laboratories, to cautiously hope that people who have been vaccinated three times may not be as vulnerable to Omicron as was first feared.

Though Dr. Maor met with many people last week, almost all of them were health care workers or close family members. And the people he had spent the most time with were fully vaccinated and had even recently had a third “booster” shot.

It is important not to extrapolate too much from isolated cases, said Prof. Gili Regev-Yochay, director of the infectious disease epidemiology unit at Sheba, who has helped lead research into the virus. “But this does tell us that, in some cases, Omicron is not as infectious if you’re vaccinated,” Professor Regev-Yochay said. “And I think that’s a major thing.”

To Dr. Maor, who was still in isolation at home on Wednesday night, it was still concerning that he had been hit so hard by the virus, despite being fully vaccinated himself, and despite being a fit nonsmoker without any chronic medical conditions. The cardiologist spent Saturday and Sunday in bed with a fever, sore throat and aching muscles — and only began to feel considerably better on Wednesday afternoon.

“Despite everything, despite the vaccines and the booster, I was in bed for 48 hours,” Dr. Maor said in a phone interview. “If I didn’t have the vaccine, I probably would have ended up in the hospital.”

To Professor Regev-Yochay, the coronavirus expert, her colleague’s experience highlighted the need for travelers to keep testing themselves and avoid busy places for a few extra days after arriving from a country with high infection rates.

Dr. Maor arrived back last Wednesday from London, where he had attended another crowded cardiology conference. Because he had tested negative twice in London, and a third time on arrival back in Israel, he had thought he was safe to operate as normal. But his experience highlighted how the virus may not show up in tests for several days.

That shows that ideally, each new arrival to the country would be tested every morning for at least five days after they land, said Professor Regev-Yochay.

“People should be cautious,” she said. “Every day on a daily basis.”

As recently as last week, many public health experts were fiercely opposed to the Biden administration’s campaign to offer booster shots of the coronavirus vaccines to all American adults.

But the Omicron variant is starting to change all that.

Scientists do not yet know with any certainty whether the virus is easier to spread or less vulnerable to the body’s immune response. But with dozens of new mutations, the variant seems likely to evade the protection from vaccines to some significant degree.

Many of the experts who were opposed to boosters now believe that the shots may offer the best defense against the new variant. The extra doses may slow the spread, at least, buying time for vaccine makers to develop an Omicron-specific formulation, if needed.

“Based on what we know about the potential for immune evasion, I would err on the side of giving the booster,” said Dr. Celine Gounder, an infectious disease specialist at Bellevue Hospital Center who had opposed the Biden administration’s boosters-for-all push.

The administration isn’t waiting for scientific consensus. Alarmed by the preliminary reports about Omicron, officials at the Centers for Disease Control and Prevention said on Monday that all American adults should receive booster shots.

But greater support for boosters among scientists may eventually complicate efforts to deliver limited supplies of the coronavirus vaccines to poor countries. The World Health Organization has said for months that the clamor for extra doses in rich countries was robbing poorer nations of the first doses they desperately need. The agency has not changed that position.

Global Roundup

The Omicron variant could become the dominant version of the coronavirus in Europe in the next few months, the European Center for Disease Prevention and Control said on Thursday, as the continent faced a surge of new infections and deaths that has prompted many governments to tighten restrictions.

The European Union’s infectious disease agency acknowledged in a report that there were “a number of uncertainties” related to the Omicron variant, including how transmissible it is, how likely it is to cause severe symptoms and how effective existing vaccines are against it. But preliminary data already suggests that Omicron, which carries a large number of mutations compared with the original virus, has a “substantial advantage” over previous versions of the virus, the agency said.

Combating the rise of Omicron requires a multilayered approach, including initial vaccinations, booster shots for people over 40, physical distancing and ventilation of indoor spaces, according to Andrea Ammon, the agency’s director. Ms. Ammon cautioned against using blanket travel bans like those recently imposed by many European nations, and said that officials should instead maintain “carefully considered” rules for travelers, including testing, quarantining and sequencing of virus cases, and review those measures regularly.

Speaking to reporters on Wednesday, Ursula von der Leyen, the president of the European Commission, called on the bloc’s member governments to speed up vaccinations and booster shots. As more European countries consider making Covid-19 vaccination mandatory, Ms. von der Leyen said it was “understandable and appropriate” for such mandates to be discussed.

• Greece said on Thursday that it had confirmed a case of the Omicron variant in a man who arrived on the island of Crete from South Africa on Nov. 26. Health Minister Thanos Plevris told reporters that the man was isolating while the authorities carry out contact tracing. Regulations announced on Wednesday to make Covid vaccinations mandatory for residents ages 60 and over, with fines for noncompliance, were approved by parliament on Thursday.

• The Catalonia and Valencia regions of Spain, which together account for more than one-quarter of the country’s population, will require proof of vaccination to enter bars, restaurants gyms and some other venues starting on Friday. The requirement is being challenged in court in those regions, and faces opposition in some other parts of the country as well. The leader of the Madrid region, Isabel Díaz Ayuso, has promised residents that they will not need to show proof of vaccination there.

• Officials in India confirmed that they had found the Omicron variant in the southern state of Karnataka, in two people who tested positive for the coronavirus after overseas air travel. Details of the cases, including the dates when the people were tested and the places they had been, were not immediately disclosed. Officials said that both people experienced mild symptoms and later tested negative.