As lawmakers push for billions of dollars to fund the nation’s efforts to track coronavirus variants, the Biden administration announced on Wednesday a new effort to ramp up this work, pledging nearly $200 million to better identify the emerging threats.

Calling it a “down payment,” the White House said that the investment would result in a significant increase in the number of positive virus samples that labs could sequence. Public health laboratories, universities and programs run by the Centers for Disease Control and Prevention sequenced more than 9,000 genomes last week, according to the database GISAID. The agency hopes to increase its own contribution to 25,000 genomes a week.

“When we will get to 25,000 depends on the resources that we have at our fingertips and how quickly we can mobilize our partners,” Dr. Rochelle Walensky, the C.D.C. director, said at a White House news conference on Wednesday. “I don’t think this is going to be a light switch. I think it’s going to be a dial.”

The program is the administration’s most significant effort to date to address the looming danger of more contagious variants of the virus. A concerning variant first identified in Britain has infected at least 1,277 people in 42 states, although scientists suspect the true number is vastly higher.

Doubling about every 10 days, the B.1.1.7 variant that emerged in Britain threatens to slow or reverse the rapid drop of new coronavirus cases. From a peak of almost 260,000 new cases a day, the seven-day average daily rate has fallen to below 82,000, still well above the high point of last summer’s surge, according to a New York Times database.

What’s more, Dr. Walensky said that the nation had seen its first case of B.1.1.7 that had gained a particularly worrying mutation that has been shown in South Africa to blunt the effectiveness of vaccines.

Other worrisome variants have also cropped up in the United States, including one that was first found in South Africa and weakens vaccines.

The F.D.A. is preparing for a potential redesign of vaccines to better protect against the new variants, but those efforts will take months. In the short term, experts say, it is critical to increase sequencing efforts, which are too small and uncoordinated to adequately track where variants are spreading, and how quickly.

Scientists welcomed the new plans from the Biden administration. “It’s a huge step in the right direction,” said Bronwyn MacInnis, a geneticist at the Broad Institute.

Dr. MacInnis said that the “minimal gold standard” would be sequencing 5 percent of virus samples. If cases continue to fall, then 25,000 genomes a week would put the country near that threshold, she said, which is “where we need to be to be detecting not only known threats, but emerging threats.”

Trevor Bedford, an evolutionary biologist at the Fred Hutchinson Cancer Research Center, said there had been “substantial gains” in national sequencing efforts since December. Still, he said that the C.D.C. would also need to make improvements in gathering data about the genomes — such as tying it to information from contact tracing — and then supporting the large-scale analysis on computers required to quickly make sense of it all.

“There’s too much of a focus on the raw count that we’re sequencing, rather than turnaround time,” he said.

White House officials cast the sequencing ramp-up as part of a broader effort to test more Americans for the virus. The Department of Health and Human Services and the Defense Department on Wednesday announced substantial new investments in testing, including $650 million for elementary and middle schools and “underserved congregate settings,” like homeless shelters. The two departments are also investing $815 million to speed the manufacturing of testing supplies.

The C.D.C.’s $200 million sequencing investment is dwarfed by a program proposed by some lawmakers as part of an economic relief package that Democratic congressional leaders aim to pass before mid-March. Senator Tammy Baldwin, Democrat of Wisconsin, introduced legislation to enhance its sequencing efforts. House lawmakers have allocated $1.75 billion to the effort.

When President Biden set a goal last year of 100 million Covid-19 vaccine shots in the first 100 days of his presidency, it now seems that he was aiming low. With the pace of vaccinations quickly rising in the United States, the nation appears likely to get there with more than a month to spare.

About 36.6 million doses have been given in the first four weeks of Mr. Biden’s presidency, bringing the total doses administered to about 56.3 million, as vaccinations have steadily increased since December. The country has averaged 1.64 million doses a day over the last week. (The vaccines that have so far been authorized in the United States involve two doses given several weeks apart, so the number of people who have been fully vaccinated by now is much smaller.)

Mr. Biden said on Tuesday night that the way things are going, vaccines should be available to anyone in the country who wants one “by the end of July,” a timeline made shorter by increasing production and by the prospect that a third vaccine, made by Johnson & Johnson and administered in a single dose, nears authorization.

The White House also said that states will collectively begin receiving 13.5 million doses each week, a jump of more than two million, in part because of a shift in how the doses in each vial of the Pfizer vaccine are being counted. Administration officials have framed regular increases in dose allocations as Mr. Biden’s accomplishment, though supplies were expected to grow as Pfizer and Moderna, the makers of the two authorized vaccines, ramped up manufacturing.

Even if the pace of vaccination stays where it is now, Mr. Biden’s initial goal would be met in late March, around Day 67 of his presidency. If the pace keeps rising and reaches 2 million doses a day, the nation could hit the 100-million-shot mark by Day 60.

“When he first announced it, it did seem like an ambitious goal,” said Dr. Eric Toner, a senior scholar at the Johns Hopkins Center for Health Security. But by Inauguration Day, it was a “low bar,” he said, and now, “something catastrophic would have to happen to keep us from achieving the 100 million doses.”

Mr. Biden first announced the benchmark on Dec. 8, several days before the first shot was given in the country outside of a clinical trial. By the time he was sworn in on Jan. 20, the nation was putting nearly 1 million shots into arms each day, adding to the roughly 19.7 million doses given before he took office.

In all, counting both before and after the change of administration in Washington, about 56.3 million doses have been administered, and about 15.5 million Americans have been fully vaccinated so far, according to data from the Centers for Disease Control and Prevention.

As the president’s initial goal has come within reach, attention has been shifting to the more meaningful challenge of getting vaccine doses to everyone who wants them.

With states expanding their inoculation programs and the federal government gradually expanding supply, Dr. Toner said, the country may be able to administer as many as 3 million doses a day within a few months, twice the pace that Mr. Biden identified in January as a target. That could rein in the spread of the virus to the point that state and local governments could ease restrictions, Dr. Toner said, provided they were careful not to relax too quickly.

“That could get us where we want to go,” he said. “Sometime over the summer, we want life to be looking fairly normal again.”

Noah Weiland contributed reporting.

For months, Assemblyman Ron Kim has been one of the few Democratic lawmakers willing to criticize Gov. Andrew M. Cuomo of New York for his handling of the state’s nursing homes during the pandemic, pressing for investigations into the matter.

Mr. Kim had told the The New York Post last Thursday that it appeared the governor was “trying to dodge having any incriminating evidence” after a top aide to Mr. Cuomo admitted that his administration had withheld nursing home data from state lawmakers.

Hours after he made that comment to the Post, Mr. Kim said Mr. Cuomo called him and yelled at him for 10 minutes. Mr. Kim said the governor threatened to publicly tarnish him if he did not issue a new statement clarifying his remarks.

“He goes off about how I hadn’t seen his wrath and anger, that he would destroy me and he would go out tomorrow and start telling how bad of a person I am and I would be finished and how he had bit his tongue about me for months,” Mr. Kim said. “This was all yelling. It wasn’t a pleasant tone.”

On Wednesday, the governor used his news briefing to lob allegations of impropriety at the assemblyman, saying that he and his administration have had a “long and hostile relationship” with Mr. Kim, now in his fifth term.

Mr. Cuomo accused the assemblyman of a “continuing racket” soliciting donations from nail salon owners, who were upset about a 2015 nail-salon reform law.

A spokesman for the governor, when asked about Mr. Cuomo’s call with Mr. Kim, initially suggested that the governor’s remarks on Wednesday had sufficiently addressed the issue.

But after this article was published, the spokesman, Richard Azzopardi, said that Mr. Cuomo had only asked Mr. Kim to clarify his remarks because the assemblyman had told him that they were taken out of context in the Post article.

Cuomo officials added that the governor never said that he would “destroy” Mr. Kim, and characterized the conversation between the two men as “calm,” denying the governor yelled.

Mr. Cuomo also was angered and combative about a letter published by The New York Post that was signed by several Assembly members, including Mr. Kim. The letter, citing the governor’s delays in releasing a complete tally of deaths of nursing home residents, accused Mr. Cuomo of attempting to circumvent a federal probe and “intentional obstruction of justice.”

Mr. Cuomo has strongly denied any wrongdoing.

The Cuban government says it is on the brink of an extraordinary scientific achievement: the mass production of a coronavirus vaccine invented on the island.

One of the four vaccines developed by Cuban scientists will enter a final phase of testing next month, a crucial step toward regulatory approval that, if successful, could put the island on the path to inoculate its entire population and begin exports by year’s end.

If the vaccine proves safe and effective, it would represent a significant political victory for the Cuban government — and a chance to rescue the nation from economic ruin. For a country that has for decades touted its sophisticated health care system as evidence of the benefits of socialism, the vaccine also offers a unique public relations opportunity.

The vaccine heading for a final phase of trials is called Sovereign 2, in a nod to the pride the island takes in its autonomy, despite decades of hostility from its neighbor to the north. Already, Cuba is floating the idea of enticing tourists to its shores with the irresistible cocktail of sun, sand and a shot of Sovereign 2.

Vicente Vérez, one of the scientists leading the team that developed the vaccine, has said that the island could offer vaccinations to all foreigners who travel there.

Cuban scientists say the government will probably give away some doses to poor countries, in keeping with its longstanding practice of strengthening international relations by donating medicine and sending doctors to address public health crises abroad.

Cuba began to pour money into biotech in the 1980s, as part of Fidel Castro’s drive to make the nation self-sufficient in the face of a U.S. embargo that made it difficult to obtain drugs produced abroad. That investment gave rise to dozens of medical research institutions and a surplus of doctors who can travel on those medical missions.

In 2019, the leasing of doctors, nurses and technicians brought in $5.4 billion, twice as much as tourism, a major driver of the economy.

As for the biotech sector, Cuba makes eight of the 12 vaccines administered to children on the island and exports vaccines to more than 30 countries.

The plan to open Covid-19 vaccination to tourists appears to some to be a risky and shrewdly capitalist gambit to attract visitors, and with them the hard currency the island desperately needs. The combination of the pandemic and sanctions have created the worst economic crisis the country has experienced since the fall of the Soviet Union in the 1990s, experts say.

Cuban scientists, however, insist the goal is to spread health. Any profit, they say, is merely a side effect.

Michigan prison officials said Wednesday that a variant of the coronavirus that is more contagious and potentially more deadly than others has swiftly infected 90 people at a state prison.

The outbreak at the Bellamy Creek Correctional Facility in Ionia is the first in a U.S. prison or jail that is known to involve the variant, called B.1.1.7. Officials said it had not caused any deaths at the prison so far.

The detection of B.1.1.7 at the prison has intensified concerns about the spread of highly transmissible variants in other correctional facilities around the nation, where Covid-19 has caused more than 615,000 infections and nearly 2,800 deaths, according to a New York Times database.

Two of the 90 people at Bellamy Creek who have tested positive for the variant are staff members and 88 are prisoners, Michigan officials said. They said they were awaiting word from the laboratory about whether the variant was present in any of another 100 recent positive tests at the prison.

As of Wednesday morning, officials did not know whether any of the 88 inmates found to be infected with the variant had been vaccinated.

Statewide, about 4,000 Michigan inmates have received coronavirus vaccinations, according to Chris Gautz, a prison spokesman; the state has about 30,000 inmates in all. It is unclear how many Bellamy Creek employees have been vaccinated, he said, because employees are not required to notify the department when they get a shot.

Mr. Gautz said that whenever one of the more than 1,600 prisoners at Bellamy Creek tests positive for the coronavirus, health officials conduct a second test to determine whether the B.1.1.7 variant is responsible. Last week, after detecting the prison’s first variant case, Mr. Gautz said, officials began a regimen of daily testing of employees and staff.

Over the course of the pandemic, about 600 inmates and 100 correctional officers at Bellamy Creek have been infected with the coronavirus so far, and one inmate has died.

Dr. Matthew Wynia, an infectious disease specialist and the director of the Center for Bioethics and Humanities at the University of Colorado, said it was not surprising that the new variant had appeared in a prison, since many states have balked at inoculating inmates before other groups.

“Prisons were generally not put high on the priority list in terms of getting vaccinated, as other congregate settings were,” he said. “So that’s where it’s going to show up.”

Studies have shown that incarcerated people are significantly more likely than others to be infected and to die from the coronavirus. Prisons and jails, Dr. Wynia said, are “petri dishes — they’re designed for the spread of a virus just like this.”

In Michigan, the prison system has offered the vaccine to inmates over the age of 65 and has sometimes given spare doses to younger inmates who have severe underlying health conditions, Mr. Gautz said.

Roughly a third of America’s military personnel are declining to receive coronavirus vaccines when they are offered, Pentagon officials said Wednesday.

The refusal rate is slightly above that of the civilian population, and is the same for active-duty troops and for those in the National Guard, who have been helping state governments administer coronavirus tests and vaccines.

About 960,000 members of the military and its contractors have been vaccinated, Robert G. Salesses, the acting assistant secretary of defense for Homeland Defense and Global Security, told members of the House Armed Services Committee at a hearing on Wednesday. As in the civilian world, the priority for administering vaccinations has been people working in heath care and those over 65.

The Pentagon can require troops to receive standard immunizations, but it cannot make Covid-19 vaccination mandatory, at least for now. That is because the vaccines have been released through federal emergency use authorizations, rather than through the normal, much lengthier approval process. So all the military can do is urge troops to get the shots, not order them to.

“We think it’s important that the department continues to communicate to our service members the safety of the vaccine,” Maj. Gen. Jeff Taliaferro, vice director of operations for the Joint Chiefs of Staff, said at the hearing. He added that troops who decline the vaccine are still permitted to deploy overseas.

For the nation’s entire history, the military has recognized that disease can be far more lethal than an enemy, and it has repeatedly forced troops to be vaccinated. In 1777, George Washington was the first military leader commanding troops to take action to prevent an epidemic by ordering all of his troops to be inoculated against smallpox. That primitive vaccine posed a risk of death. Washington wrote at the time, “This expedient may be attended with some inconveniences and some disadvantages, but yet I trust in its consequences will have the most happy effects.”

In the generations since, the military has mandated troops be vaccinated against a growing list of diseases, including typhoid in 1911, tetanus in 1941, and anthrax in 1997. Today, troops are required to have several other vaccines to travel overseas.

In a recent poll by the Kaiser Family Foundation, 31 percent of respondents from the general public said that they would wait until the vaccine “has been available for a while to see how it is working for other people” before getting the shot themselves. Various news reports and studies have found that refusal rates are highest among Republicans and among Hispanic adults, including many who work in health care.

Defense officials said they were studying the demographics of those in uniform who decline the vaccines, and had reached no conclusions yet.

Most states have relied on National Guard personnel to help respond to the pandemic, including assisting with vaccine distribution and even putting shots in arms.

The Biden administration recently announced that it would open 100 new vaccination sites around the country, operated by the Federal Emergency Management Agency and assisted by hundreds if not thousands of active-duty service members. About 1,100 troops have been deployed at the five centers that have been set up so far.

Dave Philipps contributed reporting.

global roundup

TOKYO — Japan began its national coronavirus vaccination program on Wednesday, starting with the first of 40,000 medical workers and planning to reach the general population by the summer.

The comparatively late start has raised questions at home and abroad about whether the country will be ready to host the Olympics, which are scheduled to begin in Tokyo this July after the pandemic forced a one-year delay.

Japan has managed to keep coronavirus infection levels relatively low and, so far, has recorded around 7,200 deaths. But the authorities declared a one-month state of emergency in early January, after daily case counts reached nearly 8,000. They have since extended it until at least the beginning of March, partly in response to more contagious coronavirus variants.

The vaccine rollout has been slower than in many other developed countries in part because the authorities requested that Pfizer run separate medical trials in Japan. That reflected some public ambivalence toward vaccinations, a general sense of caution that most recently surfaced after media reports about rare side effects related to vaccines for HPV.

Speaking to the news media on Tuesday, Taro Kono, the minister in charge of the rollout, emphasized that it was important to “show the Japanese people that we have done everything possible to prove the efficacy and safety of the vaccine.”

While that slowed the program’s start, he said, “We think it will be more efficient.”

Major obstacles to a rapid rollout remain. Japan relies on other countries for its entire vaccine supply and is still working to approve the vaccines from AstraZeneca and Moderna. It is also short of the special syringes that would allow its doctors to extract an extra, sixth dose from each vial supplied by Pfizer.

In his remarks on Tuesday, Mr. Kono said the vaccination program was not linked to the Games.

Speaking on Wednesday, the governor of Shimane Prefecture, which has recorded only 280 cases, threatened to pull it out of activities around the Olympic torch relay for fear of spreading infection.

In other developments across the world:

• President Cyril Ramaphosa of South Africa received the single-dose Johnson and Johnson vaccine on Wednesday, hours after 80,000 doses arrived in the country. Health care workers will be among the first to receive the vaccine. The country paused its rollout of the AstraZeneca vaccine this month after a study suggested that it failed to prevent mild or moderate illness from a variant found in the country. South Africa has recorded nearly 1.5 million coronavirus infections since the start of the pandemic, with 48,855 deaths, according to a New York Times database.

• The European Commission, the executive arm of the European Union, secured a contract for an additional 300 million doses of the Moderna vaccine, the commission’s president, Ursula von der Leyen, announced on Wednesday. The deal allows European countries to order up to 150 million doses in 2021, with an option for as many next year and authorization to donate unused doses to other countries. The commission, which has been under intense scrutiny following the sluggish vaccination rollout across Europe, had previously signed a contract for 160 million doses.

• The Gaza Strip received its first 2,000 doses of a coronavirus vaccine on Wednesday after Israel approved their delivery. The Russian-made vaccines were delivered amid a heated debate over whether Israel bears responsibility for the health of Palestinians living in occupied territory.

• The only things keeping Rio de Janeiro’s famous Carnival faintly alive are the online events produced by groups that traditionally put on extravagant street performances. The celebrations have endured during times of war, violence and the flu, but this year, Covid-19 has forced local officials across Brazil, one of the countries hit hardest by the pandemic, to cancel the festivities.

• Hong Kong plans to relax restrictions on a range of businesses on Thursday, provided they enforce use of a government-made app for contact tracing or keep records of customers. Employees must also be tested for the coronavirus every two weeks. Separately, on Tuesday, vaccine experts appointed by the Hong Kong government recommended the use of the Sinovac vaccine, a sign that health authorities will approve it for the city’s 7.5 million residents. They approved the Pfizer-BioNTech vaccine in January.

• Prosecutors in China said that a batch of fake coronavirus vaccines had been shipped outside the country last year, the state-run Xinhua news agency reported on Monday. The fake vaccines were produced by a counterfeiting ring that the authorities broke up in February. Prosecutors said last week that the ring had manufactured and sold about 580,000 vials, for a profit of almost $280 million. The police have also arrested suspects they say smuggled 2,000 vials into Hong Kong, believing them to be genuine. Prosecutors said that 600 of those vaccines were later sent overseas, but did not say where.

• Health authorities in Germany have documented rapid growth in the more infectious coronavirus variant first found in Britain, despite a general drop in new infections during a monthslong lockdown. Jens Spahn, the German health minister, said during a news conference on Wednesday that the variant now accounted for 22 percent of tested coronavirus samples, up from 6 percent at the beginning of February.

In an attempt to learn more about how a person’s immune system responds to the coronavirus, researchers will purposefully administer the virus in the coming weeks to a small group of carefully selected volunteers in a London hospital.

As many as 90 people from ages 18 to 30 could be a part of the plan that was authorized by British regulators on Wednesday. Tiny droplets of the virus will be administered into the nostrils of unvaccinated volunteers to deliberately infect them with the coronavirus.

By controlling the amount of the virus people are subjected to and monitoring them from the moment they are infected, scientists are hoping to discover things about how the immune system responds to the coronavirus that would be impossible outside a lab — and to develop ways of directly comparing the efficacy of treatments and vaccines.

Scientists hope to eventually expose vaccinated people to the virus as a way of comparing the effectiveness of different vaccines. But before that, the project’s backers have to expose unvaccinated volunteers in order to determine the lowest dose of the virus that will reliably infect them.

“We are going to learn an awful lot about the immunology of the virus,” Peter Openshaw, an Imperial College London professor involved in the study, said on Wednesday. He added that the study would be able “to accelerate not only understanding of diseases caused by infection, but also to accelerate the discovery of new treatments and of vaccines.”

The idea of such a study, called a human challenge trial, has been hotly debated since the early months of the pandemic.

In the past, scientists have deliberately exposed volunteers to diseases like typhoid and cholera to test vaccines. But infected people could be cured of those diseases; Covid-19 has no known cure, putting the scientists in charge of the British study in largely uncharted ethical territory.

But there have been severe Covid-19 cases even in young patients — the group being infected — and the long-term consequences of an infection are also largely unknown. The study’s age range may also make it difficult to translate its findings to older adults or people with pre-existing conditions, whose immune responses may be different.

“It will be a limited study,” said Ian Jones, a professor of virology at the University of Reading who is not part of the study. “And you could argue that, by definition, it’s not going to study those in whom it’s most important to know what’s going on.”

Gov. Andrew M. Cuomo of New York announced on Wednesday that outdoor amusement parks, indoor entertainment centers and summer camps would be able to reopen, with restrictions, in the coming months, even though coronavirus cases and deaths in the state remain high.

Mr. Cuomo said that indoor entertainment centers could open at 25 percent capacity on March 26; outdoor amusement parks could reopen at 33 percent capacity on April 9, with tickets sold in advance; and summer camps could plan on reopening in June.

Temperature checks and face coverings would be required at amusement parks and centers, and attractions where social distancing or easy, frequent cleaning were not possible would remain closed. Testing protocols will be required for summer camps.

“No parent is going to send their child to a summer camp unless there is a testing protocol anyway,” Mr. Cuomo said on a phone call with reporters on Wednesday.

The governor said that the reopening plans were contingent on virus cases’ continuing to drop in the state, and described current trends as encouraging. He said that New York’s seven-day average positive test rate was at 3.6 percent, the lowest it has been since late November. But at the same time, in the past two weeks, the state has had more cases and deaths per capita than any state except South Carolina, according to a New York Times database.

More contagious variants of the virus still posed a threat, the governor said, particularly one that was first discovered in Britain. Mr. Cuomo said that 82 cases of the variant had been discovered in New York, with 12 new ones confirmed since Saturday.

He also announced that in the first week of March the state would open four more mass vaccination sites in partnership with the federal government, like the two that are set to open in Brooklyn and Queens. The sites, at the New York National Guard Armory in Yonkers, the Delavan Grider Community Center in Buffalo, the Washington Avenue Armory in Albany and a parking lot near the former Kodak Hawkeye building in Rochester, are intended for underserved communities. Each will aim to vaccinate 1,000 people a day, he said.

“It is very important that the distribution be fair,” Mr. Cuomo said. “This is a precious resource; everybody wants it.”

The governor said that vaccine distribution would be impaired by the winter storms that have battered the country this week.

Mayor Bill de Blasio of New York City said on Wednesday that storms had delayed shipments of the vaccine and prevented officials from scheduling 30,000 to 35,000 vaccination appointments.

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Winter Storm Delayed Vaccine Shipments to N.Y.C., Mayor Says

Mayor Bill de Blasio said dangerous winter weather across the country had delayed Covid-19 vaccine shipments to New York and prevented officials from scheduling 30,000 to 35,000 appointments.

“We’ve got fewer than 30,000 first doses on hand right now. That means we’re going to run out today, tomorrow. We’re going to run out of what we have now. Once again, we’re in this ridiculous situation. We have massive ability to give people vaccination. We could be doing hundreds of thousands of more each week. And we’re running out of vaccine because we’re not getting what we need.” “And on top of that, we’ve got the weather problem. All over the nation, there’s huge storms that are now causing delays in shipments. So I’ve been updated this morning on the fact that we unfortunately do expect vaccine to be delayed, shipments of vaccine that we were expecting by yesterday, today, to be delayed. That means we’re going to have to hold back appointments that New Yorkers need because the vaccine isn’t arriving. Based on the information I’ve got now, as many as 30, 35,000 appointments or more might not be scheduled because we don’t have vaccine. So, appointments we would have been putting up, available to people right now, we have to hold them back because the vaccine hasn’t arrived.”

The dangerous winter weather has delayed shipments of vaccine doses to New York City, Mayor Bill de Blasio said on Wednesday, preventing officials from scheduling between 30,000 and 35,000 new vaccination appointments, delaying the opening of two new vaccination sites, and complicating a rollout already constrained by a limited supply of doses.

The problems in New York City, which could extend to suburbs and neighboring states, came as vaccination efforts have been disrupted nationwide. Clinics have closed and shipments have been stalled as snow and ice grounded flights and made highways dangerously slick. Many of the closures and cancellations have been in the South, where the storm hit hardest, with Texas, Alabama, Georgia and Kentucky canceling or rescheduling appointments.

Jeffrey D. Zients, President Biden’s coronavirus response coordinator, said on Wednesday that the Biden administration was pushing governors to extend the hours of vaccination sites once they reopen.

“People are working as hard as they can, given the importance of getting the vaccines to the states and to providers, but there’s an impact on deliveries,” he said.

Mr. de Blasio said he did not know when the shipments would arrive next or which specific weather conditions were snarling the shipments.

New vaccination sites in Queens and on Staten Island would not open on Thursday as scheduled because of the delays, the mayor said in a statement on Wednesday night, calling on pharmaceutical companies to solve supply problems. “Step up and give us the doses we need to vaccinate the people of our city,” he said. “There is not a moment to waste.”

In New York City, like other places across the country, the demand for vaccinations far outstrips the supply allocated each week. Mr. de Blasio said that the city had about 30,000 doses on hand, and that those could run out by Thursday.

“We could be doing hundreds of thousands more each week,” he said.

A heavy snowstorm this month forced city and state officials to delay appointments for days until driving conditions improved, and New York is expecting about six inches of snow on Thursday.

The commander of the U.S. base at Guantánamo Bay, Cuba, shut down most community activities at the base overnight Tuesday, barring dining in restaurants and closing gyms and the school for sailors’ children after some residents tested positive for the coronavirus at the isolated post.

Clergy members marking Ash Wednesday held a “drive-through distribution of ashes” in the chapel parking lot, near the base’s McDonalds restaurant, which switched overnight to takeout only.

The closures are “a precautionary measure after a small number of personnel tested positive for Covid-19,” said Nikki L. Maxwell, a base spokeswoman. Those who tested positive and people who may have come in contact with them were in quarantine as of Wednesday night. More testing was underway.

The last time the base took similar action was in October, after someone at the base initially tested positive for the virus. Community activities were restricted for 10 days while health officials conducted new tests and sent samples to the mainland United States for analysis. The case turned out to be a false positive.

A base-wide notice to the base’s 6,000 residents said the latest restrictions would be temporary, but offered no specifics. Saying that the impacts of the closures “on our personnel, family members, services and daily life are understood,” the notice thanked residents for their “enduring patience and support.”

Health workers at Guantánamo have been offering residents the Moderna vaccine in phases for more than a month. Shuttle bus drivers, commissary workers, schoolteachers, intelligence analysts, bartenders and Marines who guard the fence line separating the base from a Cuban minefield are among those now eligible for shots.

After a public outcry, the Pentagon postponed plans to vaccinate the 40 wartime prisoners who are held in a restricted area at the base. The 1,500 troops who staff the detention facility have been offered vaccination, according to a spokesman for the U.S. Southern Command. The military has declined to say how many of those troops, mostly National Guard soldiers on nine-month rotations, accepted the offer.

Covid-19 vaccinations are voluntary for Department of Defense personnel because the vaccines are being distributed under an emergency use authorization.

Guantánamo Bay reported two confirmed cases of residents with coronavirus in March and April, before the Pentagon curbed disclosures of the number of cases at individual bases. Both people were put in isolation and recovered, the military said.

The Navy requires everyone arriving at the base to be quarantined for two weeks.