As countries jostle to secure enough vaccine doses to help put an end to the pandemic, a new competition is unfolding: for syringes to administer them with.

There is simply not enough of them.

Officials in the United States and the European Union have said they need more. And in January, Brazil restricted exports of syringes and needles when its vaccination efforts fell short.

Further complicating the challenge, not just any syringe will do the trick.

Japan revealed last month that it might have to discard millions of doses of the Pfizer-BioNTech vaccine if it couldn’t secure enough syringes able to draw out a sixth dose from vials. In January, the Food and Drug Administration advised health care providers in the United States that they could extract more doses from the Pfizer vials after hospitals there discovered that some contained enough for a sixth — or even a seventh — shot.

“A lot of countries were caught flat-footed,” said Ingrid Katz, the associate director of the Harvard Global Health Institute.

The world needs between eight billion and 10 billion syringes for Covid-19 vaccinations alone, experts say.

In previous years, only 5 percent to 10 percent of the estimated 16 billion syringes used worldwide were meant for vaccination and immunization, said Prashant Yadav, a senior fellow at the Center for Global Development, a think tank in Washington, and an expert on health care supply chains.

Wealthier nations like the United States, Britain, France and Germany pumped billions into developing the vaccines, but little public investment has gone into expanding manufacturing for syringes, Mr. Yadav said.

The industry has ramped up to meet demand.

Becton, Dickinson and Company, which is the world’s largest manufacturer of syringes and is based in New Jersey, said it was producing 2,000 each minute to meet orders of more than a billion.

The United States is the world’s largest syringe maker by sales, according to Fitch Solutions, a research firm. The United States and China are neck and neck in exports, with combined annual shipments worth $1.7 billion.

While India is a small player globally, Hindustan Syringes & Medical Devices in Ballabgarh, one of the world’s largest syringe makers, sunk millions of dollars into preparing its syringe factories for the vaccination onslaught.

Rajiv Nath, the company’s managing director, added 500 workers to his production lines, which crank out more than 5,900 syringes per minute at factories spread over 11 acres in a dusty industrial district outside New Delhi. With Sundays and public holidays off, the company churns out nearly 2.5 billion a year, and plans to scale up to three billion by July.

Mr. Nath has sold 50 million to the Japanese government, he said, and over 400 million to India for its Covid-19 vaccination drive, one of the largest in the world.

More are waiting in line, including UNICEF. In November, the United Nations agency for children reached out to say that it was desperately seeking syringes. And not just any would do. They had to be smaller than usual, and break if used a second time, to prevent spreading disease through accidental reuse.

Most important: UNICEF needed them in vast quantities. Now.

“I thought, ‘No issues,’” said Mr. Nath. “We could deliver it possibly faster than anybody else.”

The company is set to begin shipping 3.2 million of those syringes soon, UNICEF said, provided they clear another quality check. And Mr. Nath has offered to produce about 240 million more.

The images above tell a story of disparity of the starkest sort.

“People of color are getting vaccinated at rates below their representation of the general population,” Dr. Marcella Nunez-Smith, the chair of President Biden’s coronavirus equity task force, said at a recent forum on the vaccine. “This narrative can be changed. It must be changed.”

In recent days, The New York Times’s graphics team set out to measure how equitably Covid-19 vaccines were being distributed across the United States.

The data is imperfect. As of March 3, only 38 states publicly shared race and ethnicity data for vaccinated people.

Further complicating the task, different jurisdictions define race and ethnicity categories in slightly different ways — and with different levels of completeness. In some states, as much as a third of vaccinations were missing race and ethnicity data.

But a disturbing portrait nevertheless emerged.

Communities of color, which have borne the brunt of the Covid-19 pandemic in the United States, have also received a smaller share of available vaccines. The vaccination rate for Black Americans is half that of white people, and the gap for Hispanic people is even larger, The Times analysis found.

Scientists in Oregon have identified a homegrown version of a fast-spreading variant of the coronavirus that first surfaced in Britain — but this one has a mutation that may make the variant less susceptible to vaccines.

The researchers have so far found just a single case of this formidable combination, but genetic analysis suggested that the variant had been acquired in the community and did not arise in the patient.

“We didn’t import this from elsewhere in the world — it occurred spontaneously,” said Brian O’Roak, a geneticist at Oregon Health and Science University who led the work. He and his colleagues participate in the Centers for Disease Control and Prevention’s effort to track variants, and they have deposited their results in databases shared by scientists.

The variant originally identified in Britain, called B.1.1.7, has been spreading rapidly across the United States, and accounts for at least 2,500 cases in 46 states. This form of the virus is both more contagious and more deadly than the original version, and is expected to account for most infections in America in a few weeks.

The new version that surfaced in Portland has the same backbone as B.1.1.7, and the mutation it carries — E484K, or “Eek” — is one seen in variants of the virus circulating in South Africa, Brazil and New York City.

Lab studies and clinical trials in South Africa indicate that the Eek mutation renders the current vaccines less effective by blunting the body’s immune response. (The vaccines still work, but the findings are worrying enough that Pfizer-BioNTech and Moderna have begun testing new versions of their vaccines designed to defeat the variant found in South Africa.)

The B.1.1.7 variant with Eek also has emerged in Britain, but the virus identified in Oregon seems to have evolved independently, Dr. O’Roak said.

Dr. O’Roak and his colleagues found the B.1.1.7 variant with Eek among coronavirus samples collected by the Oregon State Public Health Lab from an outbreak in a health care setting. Of the 13 test results they analyzed, 10 turned out to be B.1.1.7 alone, and one the combination.

Experts said the discovery was not surprising, because the Eek mutation has arisen in forms of the virus all over the world. But the mutation’s occurrence in B.1.1.7 is worth watching, they said.

Vaccine hesitancy has been a concern among U.S. public health experts for months now. But evidence increasingly suggests that as vaccination rates increase, many unvaccinated Americans are becoming more comfortable with the idea of receiving the shot themselves.

The proportion of adults in the country who intend to get vaccinated has increased significantly over the last several months, according to a survey released Friday by the Pew Research Center. Sixty-nine percent of the public now plans to get vaccinated — or already has — up from 60 percent who said in November that they intended to pursue it.

The issue has become more partisan over time, however. The new survey finds a 27-percentage point political gap, with 83 percent of Democrats saying they plan to get the vaccine or have already received it, compared to just 56 percent of Republicans.

Despite the divides, the new survey bolsters optimism that overall, Americans are increasingly open to receiving the vaccine. About 54 million people — 16 percent of the population — had received at least one dose of a Covid-19 vaccine as of Thursday, according to the Centers for Disease Control and Prevention.

The survey also notes that 47 percent of Black Americans plan to get vaccinated and 15 percent say they already have been. Taken together, that is a sharp increase from the 42 percent who said in November they intended to be vaccinated.

Black and Latino people in the United States are being vaccinated at lower rates in part because they face obstacles like language barriers and inadequate access to digital technology, medical facilities and transportation. Mistrust in government officials and doctors also plays a role, experts say, and is fed by misinformation that is spread on social media. President Biden has made equity a major focus of his pandemic response, saying he wants pharmacies, mobile vaccination units and community clinics that help underserved communities to help increase the pace of vaccinations.

Overall, those surveyed by Pew who say they do not plan to get the vaccine cite reasons including concerns about side effects and a feeling that the vaccines were developed too quickly. Others say they are waiting for more information about how well they work.

The Pew results echo a survey released last week from the Kaiser Family Foundation that found vaccine hesitancy declining among most demographic groups. That survey also found a significant political gap, but noted that both Democrats and Republicans were significantly more likely to say they intended to get the vaccine now than in December.

Since Johnson & Johnson revealed data showing that its vaccine, while highly protective, had a slightly lower efficacy rate than the ones produced by Moderna and Pfizer-BioNTech, health officials have feared that the new shot might be viewed by some Americans as the inferior choice.

But the early days of its rollout suggest something different: Some people are eager to get it because they want the convenience of a single shot.

And public health officials are enthusiastic about how much faster they can get the single-shot doses distributed, particularly in vulnerable communities that might not otherwise have access to vaccine.

“This is a potential breakthrough,” said Dr. Joseph Kanter, the top health official in Louisiana.

With its first allotted doses, that state is holding a dozen large Johnson & Johnson vaccination events at civic centers and other public places, modeled after what has worked for flu vaccines.

Only four million doses were shipped this week, and the company’s manufacturing lags mean that it will be at least a month before states start receiving significant supplies. But as Johnson & Johnson ramps up production over the next few months, Dr. Kanter said, the vaccine will allow his state to slash costs for staffing and operations related to second doses.

“The J. & J. vaccine brings a lot to the table,” he said.

Judged by how well it prevents severe disease, hospitalization and death, the Johnson & Johnson shot is comparable to those made by Moderna and Pfizer-BioNTech. And although it has a lower overall efficacy rate in the United States — 72 percent, compared with roughly 95 percent for the others — experts say that comparing those numbers is problematic because the companies’ trials were conducted in different places and at different times.

Besides being a single-dose shot, the Johnson & Johnson vaccine offers another benefit: It can be kept at normal refrigeration temperatures for three months. That makes it ideal for distribution at nonmedical sites such as stadiums and convention centers. The vaccine has caused a surge of excitement at small, independent pharmacies, too.

Many state health officials said they were focused on getting the vaccine to people who might be harder to reach for a second dose, such as those who are homeless or on the verge of release from prison.

Patricia Cooper, a teacher in Washington, D.C., said that President Donald J. Trump’s efforts to claim credit for a vaccine last year and the label “emergency use authorization” had suggested to her that the federal government may have rushed its reviews of vaccines. That left her feeling jittery about their safety.

But Ms. Cooper said she was eager to get a shot, especially the Johnson & Johnson one.

“This one is more appealing to me,” she said. “Who likes to get stuck more than once?”

Pope Francis made an audacious return to the world stage in the midst of the pandemic on Friday when he became the first leader of the Roman Catholic church to visit Iraq, seeking to help heal a nation uniquely wounded by violent sectarianism, foreign adventurism and the persecution of minority populations, including his own Christian flock.

“I’m happy to travel again,” Francis, who has been vaccinated against the coronavirus, said after taking off his blue surgical mask to address reporters on the papal plane.

The pope’s trip sent a message that, after a year of being cooped up in Rome and fading from public consciousness, Francis wanted to elevate his profile and spend his time with those who have suffered the most.

The pope’s visit coincided with a recent return of suicide bombings, increased rocket attacks and renewed geopolitical tensions, and some of Francis’ admirers worry that his whirlwind four-day visit will exacerbate a recent spike in the country’s coronavirus cases by drawing crowds.

But his advisers and Iraq’s top prelates insisted social distancing measures would be followed and argued the trip was necessary to show Francis’ closeness to a flock that had suffered terribly. The pope’s predecessors dreamed of visiting, but those aspirations were dashed by tensions and conflict.

The pope called for an equitable distribution of vaccines to countries already scarred by “fragility and instability.” A vaccination program began just this week in Iraq, where social distancing restrictions are largely ignored.

Top aides to Gov. Andrew M. Cuomo were alarmed: A report written by state health officials had just landed, and it included a count of how many nursing home residents in New York had died in the pandemic.

The number — more than 9,000 by that point in June — was not public, and the governor’s most senior aides wanted to keep it that way. They rewrote the report to take it out, according to interviews and documents reviewed by The New York Times.

The extraordinary intervention, which came as Mr. Cuomo was starting to write a book on his pandemic achievements, was the earliest act yet known in what critics have called a monthslong effort by the governor and his aides to obscure the full scope of nursing home deaths in the state. The episode reflects the lengths to which Mr. Cuomo has gone to control data, brush aside public health expertise and bolster his position as a national leader in the fight against the coronavirus.

The details contradict the timeline and motivation Mr. Cuomo offered in recent weeks, when he released the complete data after the state attorney general, Leticia James, revealed that thousands of deaths of nursing home residents had been undercounted, Mr. Cuomo said he had withheld the information out of concern that the Trump administration might pursue a politically motivated inquiry into the state’s handling of the outbreak in nursing homes.

But the rewriting of the report came well before requests for data arrived from federal authorities, and was accompanied by Cuomo aides’ battles with top state health officials, according to documents and interviews with six people with direct knowledge of the discussions, who requested anonymity to describe the closed-door debates.

The aides involved in changing the report included Melissa DeRosa, the governor’s top aide; Linda Lacewell, the head of the state’s Department of Financial Services; and Jim Malatras, a former top adviser to Mr. Cuomo brought back to work on the pandemic. None had public health expertise.

In response to a detailed list of questions from The Times sent on Tuesday, the governor’s office responded with a statement Thursday night from Beth Garvey, a special counsel, who said “the out-of-facility data was omitted after D.O.H. could not confirm it had been adequately verified.” She added that the additional data did not change the conclusion of the report.

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President Biden’s $1.9 trillion stimulus package ground to a standstill in the Senate on Friday, as Democrats haggled among themselves over the size and duration of federal unemployment payments that are a crucial piece of the plan.

Top Democrats, working to preserve moderate support for the package, had planned to drop their effort to increase a federal unemployment payment from $300 a week to $400 but extend it for an additional month, through Oct. 4, hoping that the concession would keep the pandemic aid plan on track.

But it appeared that Senator Joe Manchin III of West Virginia, a centrist whose support they need to maneuver the plan through the 50-50 Senate where all Republicans are opposed, remained unsatisfied.

The impasse halted the measure in its tracks just as the Senate had begun voting on proposed changes. What was supposed to have been a 15-minute vote on a minimum-wage increase stretched for longer than six hours as Democrats stalled for time, huddling on the Senate floor in search of a solution to break the impasse.

The White House declined to say whether Mr. Biden had reached out to Mr. Manchin to try to secure his support. A White House official said that Mr. Biden and his team were “staying in close contact with senators to find a resolution that will deliver for Americans who need help the most.”

Another wrinkle arose late Friday as Senator Dan Sullivan, Republican of Alaska, left the Capitol in order to catch a flight to Fairbanks and attend a funeral for his father-in-law on Saturday.

A spokesman, Nate Adams, confirmed the senator’s departure on a Friday afternoon flight and said Mr. Sullivan “intended to vote against final passage of the bill and made his opposition clear” after voting against advancing the measure.

In an evenly divided Senate, Mr. Sullivan’s absence will give Democrats an extra vote of leeway as they haggle over a series of last-minute changes to the $1.9 trillion package. But it is unlikely to resolve the current impasse, given that Mr. Manchin appeared to be contemplating supporting a Republican amendment that would curtail unemployment insurance benefits.

With the existing $300-a-week payments set to lapse on March 14, Mr. Biden’s stimulus proposal and the House bill that passed last weekend to implement it would increase the jobless aid to $400 a week and extend it through the end of August.

Some moderate Senate Democrats are opposed to raising the amount, while others are concerned about the possibility that the benefits could lapse when the chamber is typically on recess and out of Washington. The revision Democrats had devised would address both issues, as well as adding a provision to make a large portion of 2020 jobless benefits tax-free.

In a brief interview, Senator Ron Wyden, Democrat of Oregon and the chairman of the Finance Committee, said the change “avoids the August cliff, secures tax forgiveness — preventing what I call the unexpected unemployment tax surprise — and keeps the caucus together.”

It was aimed at appeasing centrist Democrats who might otherwise have been tempted to vote for a Republican amendment by Senator Rob Portman of Ohio to keep the unemployment benefit at $300 per week — extending it until July but omitting any tax sweeteners — thus sapping support for the bill among other Democrats. But on Friday, Mr. Manchin did not appear ready to accept the alternative.

The White House had signaled support, with Ron Klain, the chief of staff, tweeting, “This compromise is a great result.”

The proposal, introduced by Senator Tom Carper of Delaware, was one of dozens of amendments the Senate was set to consider on Friday as it made its way through a marathon session of rapid-fire votes. The vote-a-rama, as it is known, could stretch long past midnight as Republicans battle against the bill, paving the way for a Senate vote to pass the stimulus plan as early as Saturday.

The unemployment provision would forgive up to $10,200 in taxes on benefits received in 2020. Mr. Wyden, who was among those pushing to increase the unemployment payment to $400, said on the Senate floor that he was “really hoping this brings all sides of the Senate together.”

Democrats are racing against the clock, as some Americans have already begun to file their taxes and unemployment benefits are set to begin lapsing next weekend. The agreement would also extend tax rules regarding excess business loss limitations for one additional year, through 2026.

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Canada’s health regulator on Friday authorized the use of Johnson & Johnson’s single-dose vaccine. The move now gives the country, which has experienced a slow start to vaccinations, four inoculations to choose from.

“This is great news,” Prime Minister Justin Trudeau said at a news conference. He offered no projected date for the first deliveries.

Health Canada officials said that the vaccine has an overall effectiveness of 66.9 percent, much lower than the efficacy rates reached by Pfizer and Moderna vaccines. But it is similar to those vaccines in having a powerful ability to prevent severe disease, hospitalizations and death.

The United States and Bahrain have also authorized the Johnson & Johnson vaccine.

Production delays with the Pfizer and Moderna vaccines, combined with relatively modest initial shipments, have led to frustration among many Canadians — and put political pressure on Mr. Trudeau as Canada’s vaccination rate fell far behind that of the United States, Britain and other countries. As of Friday, 2.86 percent of all Canadians have received at least one dose.

Canada has ordered 10 million doses of the Johnson & Johnson vaccine and has options for another 28 million, a combined number that is slightly higher than the country’s population.

Depending on its arrival and combined with the need to only administer a single shot, the new vaccine may help significantly boost the country’s vaccination rate. The Johnson & Johnson vaccine also does not require extremely low storage temperatures, as the Pfizer vaccine does, making it easier to distribute to remote communities in Canada’s north.

Mr. Trudeau said that Pfizer would send 1.5 million doses, originally scheduled for delivery in the summer, over the next two months. Canada also received its first shipment this week of a version of the AstraZeneca vaccine, developed by the Serum Institute of India.

The Canadian government had initially promised to obtain six million doses of vaccines by the end of March. The new Pfizer schedule combined with AstraZeneca shipments, officials said, will raise that figure to eight million.

President Biden is enjoying a level of popularity his poll-obsessed predecessor never came close to achieving — a 60 percent approval rating — with 70 percent of Americans expressing support for his handling of the coronavirus pandemic, according to a new poll.

Despite enduring and stark partisan divisions, 44 percent of Republicans approve of Mr. Biden’s actions prioritizing the fight against the virus, according to an Associated Press-NORC Center for Public Affairs Research poll released early Friday.

As a temperature check of the current national mood, the poll suggests that Republican lawmakers in Washington, who have united to oppose Mr. Biden’s $1.9 trillion coronavirus relief bill, are not swaying public opinion, despite their efforts to alter or delay its passage.

In all, 22 percent of Republicans approve of Mr. Biden’s performance, suggesting small but substantial gains among his most hard-core opponents that could give him added political leverage, paving the way for the possibility of a big bipartisan deal on infrastructure.

Mr. Biden’s overall approval among Democrats is a solid 94 percent, despite recent criticism from progressives.

Mr. Trump sustained a similar level of support from his base, but is the only president in the history of modern polling to never post an aggregate approval rating above 50 percent. His level of support has sunk, to an average of about 38 percent, after the Jan. 6 attack on the Capitol.

Friday’s poll is a bit sunnier than other recent national surveys that show a slight decrease in support for Mr. Biden as the fight over his relief package heats up on Capitol Hill. A RealClearPolitics aggregation of polls put his approval rating at 53.4 percent, not factoring in the A.P. poll.

Mr. Biden’s grades on the economy were lower than his ratings on other issues, the poll found. His approval on pocketbook issues was 55 percent. Only 17 percent of Republicans, a group that gave former President Donald J. Trump high marks for his handling of the economy even during the pandemic-related downturn, approved of Mr. Biden’s approach to the economy.

The A.P. poll, unsurprisingly, found that the atmosphere of hyper partisanship exacerbated by Mr. Trump’s four years of provocation is not subsiding under Mr. Biden, and that people in both parties tend to interpret fact through the filter of ideology.

Americans’ views on the economy have shifted dramatically even though many basic economic statistics have budged little, if at all.

In December, 67 percent of Republicans and just 15 percent of Democrats described the economy as “good,” according to an A.P. poll taken at the time. Now, 35 percent of Republicans and 41 percent of Democrats describe the economy in positive terms.

The poll, which surveyed 1,434 adults between Feb. 23 and March 1, has an overall sampling error of plus or minus 3.4 percentage points.

Cyprus has announced a plan to allow vaccinated residents of Britain to visit the island beginning in May, a further signal that countries, particular those dependent on tourism, could resort to inoculation certificates to reopen their borders.

Savvas Perdios, the deputy tourism minister for Cyprus, told the Cyprus News Agency that, as of May 1, British citizens who had received two doses of a vaccine approved by the European Union’s drug regulator would be allowed to travel to the Mediterranean island without having to be tested for the coronavirus or to isolate on arrival.

Some European nations with economies that are heavily reliant on tourism, such as Spain, have advocated for a vaccine certificate program to be created at the European Union level but have also said that they could adopt bilateral systems if no broader agreement is reached. The European Commission, the bloc’s executive arm, this week announced plans to create a “digital green pass” to facilitate safe travel among member nations, though that system is expected to take at least three months.

The British authorities have said that talks on opening up travel are underway with a number of countries, including some in the European Union.

Matt Hancock, the British health secretary, said this week, “If another country wants to say that you need to have been vaccinated with a recognized vaccine to travel there, we want to enable Brits to be able to take that journey.”

More than a million travelers from Britain visited Cyprus in 2019, representing by far the highest number of international tourists to the island, according to official statistics.

Despite the green light from Cyprus, international travel from Britain is forbidden for leisure purposes until at least May 17 under the current lockdown rules, and it is unclear how many British residents will have received two vaccine doses by then. Fewer than a million people in Britain have so far been fully vaccinated.

In other news around the world:

• South Korea’s drug safety agency approved the Pfizer-BioNTech vaccine on Friday and doses for about 23 million people are expected to begin arriving this month, the news agency Yonhap reported. The country, which has a population of about 51 million, began its vaccination program last week as part of a plan to achieve herd immunity by November. South Korea approved the Oxford-AstraZeneca vaccine in February and expects to receive more than two million doses through Covax, an international group that has negotiated for coronavirus shots.

• Prime Minister Jacinda Ardern of New Zealand has said that a snap lockdown imposed last week on the country’s largest city, Auckland, will end on Sunday morning. Social gatherings will be capped at 100 people and other restrictions will remain in place. The lockdown was imposed after the authorities discovered an untraceable case. They have since conducted more than 50,000 tests and tracked more than 6,000 contacts.

• Japan has extended its state of emergency for the greater Tokyo metropolitan area until March 21, the government announced on Friday, according to the national broadcaster NHK. Emergency orders were lifted in six other prefectures. The restrictions, which include an order for restaurants and bars to close by 8 p.m., had been scheduled to end on Sunday.

The San Diego Zoo has given nine apes an experimental coronavirus vaccine developed by Zoetis, a major veterinary pharmaceuticals company.

In January, a troop of gorillas at the zoo’s Safari Park tested positive for the virus. All are recovering, but even so, the zoo requested help from Zoetis in vaccinating other apes. The company provided an experimental vaccine that was initially developed for pets and is now being tested in mink.

Nadine Lamberski, a conservation and wildlife health officer at San Diego Zoo Global, said the zoo vaccinated four orangutans and five bonobos with the experimental vaccine, which is not designed for use in humans. Among the vaccinated orangutans was an ape named Karen, who made history in 1994 when she became the first orangutan to have open-heart surgery.

Dr. Lamberski said one gorilla at the zoo was also scheduled to be vaccinated, but the gorillas at the wildlife park were a lower priority because they had already tested positive for infection and had recovered. She said she would vaccinate the gorillas at the wildlife park if the zoo received more doses of the vaccine.

Mahesh Kumar, senior vice president of global biologics for Zoetis, said the company is increasing production, primarily for its pursuit of a license for a mink vaccine, and will provide more doses to the San Diego and other zoos when possible. “We have already received a number of requests,” he said.

Infection of apes is a major concern for zoos and conservationists. They easily fall prey to human respiratory infections, and common cold viruses have caused deadly outbreaks in chimpanzees in Africa. Genome research has suggested that chimpanzees, gorillas and other apes will be susceptible to SARS-CoV-2, the virus that has caused the pandemic. Lab researchers are using some monkeys, like macaques, to test drugs and vaccines and develop new treatments for the virus.

Scientists are worrying not just about the danger the virus poses to great apes and other animals, but also about the potential for the virus to gain a foothold in a wild animal population that could become a permanent reservoir and emerge at a later date to reinfect humans.

Infections in farmed mink have produced the biggest scare so far. When Danish mink farms were devastated by the virus, which can kill mink just as it kills people, a mutated form of the virus emerged from the mink and reinfected humans. That variant showed resistance to some antibodies in laboratory studies, raising suspicion that vaccines might be less effective against it.

That virus variant has not been found in humans since November, according to the World Health Organization. But other variants have emerged in people in several countries, proving that the virus can become more contagious and in some cases can diminish the effectiveness of some vaccines.

Denmark ended up killing as many as 17 million mink — effectively wiping out its mink farming industry. In the United States, thousands of mink have died, and one wild mink has tested positive for the virus.

Although many animals, including dogs, domestic cats, and big cats in zoos, have become infected by the virus through natural spread, and others have been infected in laboratory experiments, scientists say that widespread testing has yet to find the virus in any animal in the wild other than the one mink.

National Geographic first reported the vaccination of the apes at the San Diego Zoo.

For much of the winter, Meryl Gordon worried about the people caring for her 95-year-old mother, who was rehabbing in a Manhattan nursing home after surgery for a broken hip.

“Every week they sent out a note to families about how many staff members had positive Covid tests,” said Ms. Gordon, a biographer and professor at New York University. “It was a source of tremendous anxiety.”

Ms. Gordon feels reassured now that her mother is fully vaccinated and has returned to her assisted living facility. But what about the two home care aides who help her 98-year-old father, David, in his Upper West Side apartment?

Neither has agreed to be vaccinated. David Gordon’s doctor has advised him to delay vaccination himself because of his past allergic reactions.

Ms. Gordon has not insisted that the caregivers receive vaccinations. “You’re reluctant to do something that could cause you to lose the people you rely on,” she said. But she remains uneasy.

It’s a question that many long-term care employers, from individual families to big national companies, are confronting as vaccines become more available, although not available enough: In a pandemic, can they require vaccination for those who care for very vulnerable older adults? Should they?

Some employers aren’t waiting. Atria Senior Living, one of the nation’s largest assisted living chains, has announced that by May 1 all staff members must be fully vaccinated.

Silverado, a small chain of dementia care homes, most on the West Coast, mandated vaccination by March 1. Juniper Communities, which operates 22 facilities in four states, has also adopted a mandate.

“We felt it was the best way to protect people, not just our residents but our team members and their families,” said Lynne Katzmann, Juniper’s chief executive. Of the company’s nearly 1,300 employees, “about 30 individuals have self-terminated” because of the vaccination requirement, she reported.

Juniper’s experience supports what public health experts have said for years: Vaccine mandates, like those that many health care organizations have established for the flu vaccine, remain contentious — but they do increase vaccination rates. As of Feb. 25, 97.7 percent of Juniper residents had received two vaccine doses, and so had 96 percent of its staff members.

That stands in stark contrast to staff vaccinations in many facilities. The Centers for Disease Control and Prevention has reported that during the first month of vaccine clinics in nursing homes, only 37.5 percent of staff members received the first shot, along with 77.8 percent of residents.