Pfizer-BioNTech Vaccine Said to Be Powerfully Protective in Adolescents

President Emmanuel Macron had gambled that he could calibrate rules to check the virus. But hospitals are overwhelmed, with thousands of people in intensive care units for the first time since last April.,

LiveUpdated March 31, 2021, 8:48 a.m. ETMarch 31, 2021, 8:48 a.m. ET

No infections were recorded in children aged 12 to 15 who received shots, and they experienced no serious side effects, the companies said. In France, as cases surge, a third national lockdown looks likely.

Taking part in the Pfizer vaccine trial at Cincinnati Children's Hospital.
Taking part in the Pfizer vaccine trial at Cincinnati Children’s Hospital.Credit…Cincinnati Children’s Hospital

The Pfizer-BioNTech Covid vaccine is extremely effective in adolescents 12 to 15 years old, perhaps even more so than in adults, the companies reported on Wednesday. No infections were found among children who received the vaccine in a recent clinical trial; they produced strong antibody responses and experienced no serious side effects.

The findings, if they hold up, may well speed a return to normalcy for millions of American families. Depending on regulatory approval, vaccinations could begin before the start of the next academic year for middle school and high school students and for elementary school children not long after.

The companies announced the results in a news release that did not include detailed data from the trial, which has not yet been peer-reviewed or published in a scientific journal.

The good news arrives even as the country records an alarming rise in infections and health officials renew calls for Americans to heed precautions and get vaccinated. On Monday, Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, said that rising caseloads had left her with a sense of “impending doom.” President Biden urged Americans to keep wearing masks, whatever state officials might say.

Vaccination efforts are accelerating throughout the nation. As of Tuesday, 29 percent of adults had received at least one dose of a coronavirus vaccine, and 16 percent had been fully inoculated, according to the C.D.C.

But the country cannot hope to reach herd immunity — the point at which immunity becomes so widespread that the coronavirus slows its crawl through the population — without also inoculating the youngest Americans, some experts say. Children under 18 account for about 23 percent of the population in the United States.

The trial included 2,260 adolescents ages 12 to 15. The children received two doses of the vaccine three weeks apart — the same amounts and schedule used for adults — or a placebo of saltwater.

The researchers recorded 18 cases of coronavirus infection in the placebo group, and none among the children who received the vaccine. Still, the low number of infections makes it difficult to be too specific about the vaccine’s efficacy in the population at large, said Angela Rasmussen, a virologist affiliated with Georgetown University.

The adolescents who received the vaccine produced nearly twice the levels of antibodies on average, compared with participants 16 to 25 years of age in an earlier trial of adults. They experienced the same minor side effects as older participants, although the companies declined to be more specific.

Akiko Iwasaki, an immunologist at Yale University, said she had expected antibody levels in adolescents to be comparable to those in young adults. “But they’re getting even better levels from the vaccines,” she said. “That’s really incredible.”

She and other experts cautioned that the vaccine might be less effective in children, and adults, against some of the variants that are circulating in the United States.

Pfizer and BioNTech have begun a clinical trial of the vaccine in children under 12 and started inoculations of children ages 5 to 11 just last week. Company scientists plan to start testing the vaccine next week in even younger children, ages 2 to 5, followed by trials in children ages 6 months to 2 years.

Pfizer and BioNTech plan to request from the Food and Drug Administration an amendment to the emergency use authorization for their vaccine, in hopes of beginning vaccinations of older children before the start of the next school year.

Place de la Concorde in Paris on Tuesday. France has reported an average of about 37,000 daily new cases over the past week.
Place de la Concorde in Paris on Tuesday. France has reported an average of about 37,000 daily new cases over the past week.Credit…Ludovic Marin/Agence France-Presse — Getty Images

PARIS — More than a year after the government in France ordered its first national lockdown to fight back the Covid-19 pandemic, the authorities now seem to have little choice but to do the same again, as infections rise sharply across the country and hospitals in Paris are overflowing.

President Emmanuel Macron will address the country at 8 p.m. on Wednesday and is expected to announce new restrictions, possibly bringing in a third national lockdown, which he has long tried to avoid.

France on Tuesday reported more than 5,000 people in intensive care units for the first time since last April, with bed shortages in hospitals in the most affected areas becoming acute. And the slow vaccine rollout has not prevented an outburst of infections, as an average of about 37,000 daily new cases have been reported over the past week.

“The outlook is worse than frightening,” Jean-Michel Constantin, the head of the intensive care unit at the Pitie-Salpetriere hospital in Paris, told RMC radio on Monday.

“We’re already at the level of the second wave and we’re quickly getting close to the threshold of the first wave,” he said. “April is going to be dreadful.”

New restrictions were introduced on the regional level in mid-March in an attempt to stave off a third wave of infections, affecting about a third of the population, including the Paris region. The rules forced businesses that are considered nonessential to close, ordered residents to limit their outdoor activities to places within six miles of their homes and banned travel to or from regions where infections were rising.

But as infections nonetheless stubbornly rose, pressure has been building on Mr. Macron to implement tougher measures.

Writing in Le Journal du Dimanche, 41 doctors from the Paris region warned that hospitals may soon become so stretched that they will have to choose which patients to try to save.

“All indicators show that the current measures are and will be insufficient to quickly reverse the alarming curve of contaminations,” they wrote.

Mr. Macron, in the same newspaper, said that he would “look at the effectiveness of the containment measures in the coming days, and we’ll take others if they are necessary.”

In late January, Mr. Macron made a calculated gamble of resisting a new national lockdown, hoping that his government could tighten restrictions just enough to fight back a rise in infections.

That strategy seemed to be working until mid-March, when infections rose sharply and the vaccination campaign failed to gather speed, amid the disarray of the rollout of the AstraZeneca vaccine.

The health authorities on Tuesday said that about 8.3 million people had received at least a first shot of the coronavirus vaccine, or about 12 percent of the total population. The government plans to vaccinate 10 million people by mid-April and 30 million by the summer.

But France still lags behind some other Western countries in its vaccine rollout. Britain has vaccinated 46 percent of its population and the United States 29 percent, according to data from The New York Times.

Many doctors and epidemiologists are calling for a lockdown comparable to that of early 2020, when the authorities enforced some of the strictest Covid-19 restrictions in Europe, ordering people to stay inside except for a few exceptions. Schools, which France has kept open since last June, unlike many of its neighbors, could also be forced to close as the virus is increasingly spreading in classrooms.

Receiving a dose of the Moderna vaccine on Thursday at a site in West Farms Square Plaza in the Bronx.
Receiving a dose of the Moderna vaccine on Thursday at a site in West Farms Square Plaza in the Bronx.Credit…James Estrin/The New York Times

Even as much of the rest of the country has had a reprieve, New York City has remained a coronavirus hot spot, with new cases holding level, often at about 25,000 a week.

As variants and vaccinations have taken hold, public health experts have debated what to call the current, confusing phase of the epidemic, when cases remain alarmingly high, but hope is drawing nearer.

“The term I’ve been using is ‘high plateau’,” said Dr. Jay Varma, a senior adviser for public health at City Hall. “We’re basically trying to come down off of our second wave and what we’re trying desperately to do is prevent a third wave.”

Since mid-February, the seven-day average of new cases in the city has largely remained between 3,500 and 4,000.

Epidemiologists and disease modelers spoke of a stalemate between the pace of vaccinations and the momentum of two new, more contagious variants that were spreading steadily across the city. Those variants now make up a majority of cases, city officials said.

Several public health experts who use prediction models believe that New York’s current upswing probably won’t reach levels that the city saw during the peak after the holiday season, when cases surged to nearly 6,500 per day on average. But the cases aren’t likely to drop much soon either.

Dr. Ronald Scott Braithwaite, a professor at N.Y.U. Grossman School of Medicine who has been modeling New York City’s epidemic and is an adviser to the city, predicted that cases would gradually rise — “not so much a wave, but a bulge,” he said — for a month or two until a critical number of people had been vaccinated.

“At our current rate of vaccination, it seems it will be mid- to late May before vaccinations win the tug of war,” Dr. Braithwaite said.

On Monday, state officials announced that all adults in New York would be eligible for vaccination starting next week, which should boost the vaccination effort as supply begins to increase.

The new normal for New York City, at least until mid-May, may well be an average positive test rate that hovers around 6 percent and a daily case rate of around 4,000.

Wan Yang, a professor of epidemiology at Columbia University’s Mailman School of Public Health, said that changing social behavior might be the tipping point that leads to a sustained upswing in cases. She noted that New York’s restrictions had eased over the past month — including looser limits around indoor dining and the reopening of indoor fitness classes — and that many New Yorkers were socializing and interacting more than before.

Tracey Tully contributed reporting.

Disinfecting a wet market in Wuhan, China, in January.
Disinfecting a wet market in Wuhan, China, in January.Credit…Gilles Sabrie for The New York Times

China on Wednesday sought to shift attention away from efforts inside its borders to trace the source of the coronavirus, arguing that health experts should start looking for clues in other countries.

A day after the World Health Organization released a report detailing the findings from a team of experts that visited the city of Wuhan, Chinese state media outlets rejected criticism from the White House and others that Beijing had not been transparent in the inquiry.

“Maybe it’s time for scientists to dig somewhere else and test more hypotheses to solve the mystery,” said an article in Global Times, a nationalistic tabloid owned by China’s ruling Communist Party.

The Chinese foreign ministry echoed that sentiment, saying in a statement that the investigation into the origins of the virus was a “global mission that should be conducted in multiple countries and localities.”

The remarks by Chinese officials clash with the prevailing view among scientists that the virus most likely emerged in China and that resources should be focused on further studies inside the country.

The 124-page W.H.O. report, written jointly by a team of 17 Chinese scientists and 17 global experts, concluded that the coronavirus probably emerged in bats before spreading to humans through an intermediate animal. But it said that China lacks the research to indicate how or when the virus began spreading, and recommended more detailed studies of the earliest infections and extensive testing of livestock and farmers in China and Southeast Asia.

Whether Beijing will cooperate in further investigations is unclear.

Chinese officials seemed skeptical of a suggestion on Tuesday by Dr. Tedros Adhanom Ghebreyesus, the W.H.O. chief, that experts should look more closely at the possibility that the virus emerged accidentally from a lab.

Hua Chunying, a spokeswoman for the Chinese Foreign Ministry, on Wednesday brushed aside suggestions that the virus could have leaked from a lab in Wuhan and said that health experts should instead look at labs around the world, including in the United States.

“We hope that if it is necessary, other relevant countries will be able to closely work with the experts of W.H.O. in a scientific, open, transparent and responsible manner like China,” she said at a news briefing in Beijing.

At a separate briefing on Wednesday, Chinese scientists who participated in the W.H.O. mission rejected criticism of the government’s refusal to share raw data about early Covid-19 cases with the W.H.O. team, which Dr. Tedros had also raised on Tuesday. Liang Wannian, a top health official, said that some data could not be shared outside China because of privacy laws.

The White House has expressed concern that the Chinese government influenced the findings of the report. After its release, 14 countries, including the United States and Britain, released a statement saying that the study was “significantly delayed and lacked access to complete, original data and samples,” and called for additional investigation.

Albee Zhang contributed research.

A main shopping street in Istanbul last week. On Wednesday, Turkey recorded its highest single-day total of new infections since the pandemic began.
A main shopping street in Istanbul last week. On Wednesday, Turkey recorded its highest single-day total of new infections since the pandemic began.Credit…Emrah Gurel/Associated Press

With coronavirus infections surging on the eve of the Muslim holy month of Ramadan, the Turkish government is reimposing strict social-distancing measures, including a prohibition on the large gatherings for meals before sunrise and after sunset that are traditionally a part of the holiday.

On Wednesday, Turkey recorded 37,303 new coronavirus cases within 24 hours, the country’s highest single-day total since the pandemic began and a fourfold increase since the beginning of March.

The sharp surge in infections — mostly from the highly contagious variant of the virus that was first identified in Britain — prompted President Recep Tayyip Erdogan to reinstate some of the restrictions he had eased just weeks ago.

With nearly two-thirds of adult intensive care beds occupied, the government has ordered restaurants to shift to takeout only and nearly the entire nation of 83 million is being ordered to stay at home on weekends.

In an address to the nation on Monday, Mr. Erdogan said that 80 percent of cities in Turkey were now considered at very high risk for the coronavirus, forcing his government to reinstate lockdown measures.

“The increase in the number of cases and patients, and deaths, obliged us to review the current practices,” he said.

But Mr. Erdogan has come under fire from opposition politicians and Turkish citizens for holding meetings of his governing party in crowded sports complexes around the country, ignoring the social distancing rules that were otherwise strictly enforced by his government. Critics also say that the authorities were too quick to begin relaxing restrictions in early March.

The new lockdowns are expected to be especially difficult for traders and small-business people, who had been hoping for an economic lift during Ramadan.

“The ones meeting at crowded congress are playing with our bread,” tweeted a group that represents cafe, bar and restaurant employees. “The whole sector is getting shut down because of the words coming from the mouth of one single person.”

Even Turkey’s health minister, Fahrettin Koca, appeared to offer veiled criticism of Mr. Erdogan, telling reporters at Parliament on Tuesday that because the virus continues to afflict Turkey, “everyone in this struggle should fulfill their own responsibility.”

Mr. Koca said that Turkey’s vaccination drive would soon gather pace with the delivery of millions more doses of the vaccine produced by the Chinese company Sinovac as well as the Pfizer-BioNTech vaccine. Since January, 6.8 million people in the country have received two doses of the Sinovac shots.

— The New York Times

A vaccination site capable of inoculating 1,000 people per day inside Salisbury Cathedral in Salisbury, England, in January.
A vaccination site capable of inoculating 1,000 people per day inside Salisbury Cathedral in Salisbury, England, in January.Credit…Andrew Testa for The New York Times

In January, Britain made a change to its vaccine guidelines that shocked many health experts: If the second dose of one vaccine wasn’t available, patients could be given a different one.

The new rule was based on sheer guesswork. There was no scientific data at the time demonstrating that mixing two coronavirus vaccines was safe and effective. But that may change soon.

In February, researchers at the University of Oxford began a trial in which volunteers received a dose of the Pfizer-BioNTech vaccine followed by a dose of AstraZeneca’s formulation, or vice versa. This month, the researchers will start analyzing the blood of the subjects to see how well the mix-and-match approach works.

As growing numbers of vaccines are being authorized, researchers are testing other combinations. A few are in clinical trials, while others are being tested in animals for now.

Mixing vaccines might do more than just help overcome supply bottlenecks. Some researchers suspect that a pair of different vaccines might work better than two doses of the same one.

“I think we’re on the cusp of some interesting data,” said Adam Wheatley, an immunologist at the University of Melbourne in Australia.

The concept of mixing vaccines — sometimes called a heterologous prime-boost — is not new to our pandemic era. For decades, researchers have investigated the approach, hoping to find potent combinations against a range of viruses, such as influenza, H.I.V. and Ebola.

But scientists had little to show for all that research. It was easy enough to demonstrate that two vaccines may work well together in a mouse. But running full-blown clinical trials on a combination of vaccines is a tall order.

Some researchers are investigating heterologous vaccines not to find a superior mixture, but simply to open up more options for countries desperate to vaccinate their populations. Last week, India held back exports of vaccines to other countries as it grappled with a Covid surge. For countries that were counting on those vaccines, a safe alternative for second doses could save lives.

Worldwide, 13 vaccines are now in use against Covid-19, with 67 more in clinical trials.

“In the current situation, we have a quite a luxurious position of having so many advanced, effective vaccines,” Dr. Wheatley said.

As the number of authorized vaccines grows, the possible combinations in which they can be used will explode.

Whether scientists carry out more experiments on other vaccines will depend on the willingness of the vaccine manufacturers. “You’re requiring quite large pharmaceutical companies to play nice together,” Dr. Wheatley said.

Dr. Bernard Moss, a virologist at the National Institute of Allergy and Infectious Diseases, suspects that a number of companies will be willing to let their vaccines be tested in combinations. “It’s always better to be a part of something that is going to be used,” he said, “than to wholly own something that isn’t.”

Ghie Ghie, center-right, and Weng, two undocumented domestic workers from the Philippines, in London this month. They said their employers had asked them to get vaccinated.
Ghie Ghie, center-right, and Weng, two undocumented domestic workers from the Philippines, in London this month. They said their employers had asked them to get vaccinated.Credit…Andrew Testa for The New York Times

LONDON — The British government said in February that everyone living in the country would be eligible for a coronavirus vaccine, free of charge, regardless of their immigration status. But many undocumented immigrants in the country are not getting inoculated.

Some are afraid that asking for a shot will get them deported. Others have been turned away at local doctors’ offices, which often ask for identification or proof of address, even though neither is required to access primary care in Britain. And many simply are in the dark about the services available to them — a lasting effect of a government policy of hobbling their access to jobs, bank accounts and free medical care in the hope of spurring them to leave the country.

“It’s all very well to say, ‘Anyone can get a vaccine,'” said Phil Murwill, head of services at Doctors of the World U.K, a humanitarian organization. “But for years, there was a deliberate policy of creating a hostile environment for undocumented immigrants that has put people off from accessing any kind of care. And we’re seeing that play out now.”

As in much of the world, the virus has ravaged immigrant communities in Britain, which supply the bulk of frontline workers in grocery stores and domestic care. The British government has not published a count of its undocumented immigrant population since 2005, but outside estimates put the number at 800,000 to 1.2 million. It is a significant group that includes many at-risk workers, and one that epidemiologists say the nation’s vaccination effort must reach if Britain hopes to safely exit the pandemic.

In the United States, efforts are underway to prioritize vaccinating those in jobs done primarily by undocumented immigrants, like farm work. But Britain did not extend its “social care” eligibility category to include domestic workers, a Department of Health and Social Care spokesperson confirmed in an email.

The department has said that anyone undergoing vaccination, testing or treatment for the coronavirus would not be subject to immigration status checks. But there are still instances in which the department shares patient information with the Home Office, which is in charge of immigration. Most commonly, it occurs when undocumented immigrants have overdue secondary-care medical bills of 500 pounds, about $690, or more. (Primary care is free.)

“The government needs to suspend all charging and data-sharing operations, if they want to prioritize the widest possible access to public health,” said Zoe Gardner, a policy adviser for the Joint Council for the Welfare of Immigrants.

Mayor London Breed of San Francisco speaking to parents, students and teachers at a rally at City Hall this month in support of reopening schools.
Mayor London Breed of San Francisco speaking to parents, students and teachers at a rally at City Hall this month in support of reopening schools.Credit…John G Mabanglo/EPA, via Shutterstock

The pandemic has brought grinding frustrations for parents, educators and students across the United States. But perhaps no place has matched San Francisco in its level of infighting, public outrage and halting efforts to reopen schools.

In February, the city sued its own school system, which has been entirely remote for a year, and board of education, accusing them of violating state law by not resuming in-person instruction.

Soon after, two parents infuriated by the school board’s decision to rename 44 schools, even as it kept them closed, started a drive to recall three of the board members. Some 9,000 people have joined the campaign’s mailing list, and they are expected to begin collecting signatures soon.

Then critics of the board unearthed four-year-old tweets written by the board’s vice president in which she accused Asian-Americans of sidling up to white Americans to get ahead without confronting racism, comparing them to slaves who benefited from working inside a slave owner’s house. More than a third of the district’s students are Asian-American.

Amid the chaos, one thing has remained clear: A large share of the city’s public school students are unlikely to see the inside of their classrooms this academic year.

The district has set dates in mid-to-late April to start bringing back elementary students and some high-needs older students, but there is no plan yet for the majority of middle or high school students to return. At the same time, all of the roughly 10,000 teachers and staff members in the district have been offered vaccinations.

In the realm of education, the pandemic has reinforced the notion of a city divided by wealth and race. Around one-third of the city’s schoolchildren, many of them white, go to private schools, one of the highest rates of any major city in the United States. Many of those private-school students have been sitting in classrooms for months while public school students, who are disproportionately Black, Latino and Asian-American, have spent the year in virtual classes.

Administering the AstraZeneca vaccine in Lviv, Ukraine, this month. Recent opinion polls have shown that about 40 percent of Ukrainians do not trust the shot.
Administering the AstraZeneca vaccine in Lviv, Ukraine, this month. Recent opinion polls have shown that about 40 percent of Ukrainians do not trust the shot.Credit…Pavlo Palamarchuk/Reuters

What does it take to get a vaccine in Ukraine? For some people, lots of Facebook friends.

Ukraine’s vaccine effort, which has been among the slowest in Europe, has been hampered by widespread hesitancy, mainly among older people who currently qualify for the shot. The problems have not been helped by the flood of often confusing and bad news around the AstraZeneca vaccine, the main option available in the country. Recent opinion polls have shown that about 40 percent of Ukrainians do not trust the shot.

To bolster acceptance, the Ministry of Health has opened vaccination to people deemed to have a public persona, regardless of their age. That includes actors, pop stars, athletes, writers, journalists — and social media influencers.

The criteria are decided locally, by city officials or doctors at vaccination sites. Those who think they have sway with the public can fill out an online form, which asks how many social media followers they have, on Facebook or on other platforms. Influencers only qualify for shots leftover at the end of the day that might otherwise be wasted.

The main requirement under the program is that recipients share their vaccination selfies on social media.

The program has drawn some bona fide opinion leaders. The Ministry of Health organized a public vaccination of leaders of different religions, for example. “The Lord sent us vaccinations,” the chief rabbi of Kyiv, Jonathan Markovitch, said, encouraging inoculation. “You definitely need to take advantage of this.”

The program was quickly flooded with young influencers. There they were, in glowing good health and at relatively little risk from the disease, posting pictures of themselves getting the shot, grinning or giving a thumbs up.

Some had fewer than a thousand followers on social media. Medical ethicists say that anybody offered a shot should take it, even if they think others may be more qualified. The recipients do not set the rules, after all, and refusing a shot can risk vaccine being wasted.

In the month since Ukraine received its first shipment of 500,000 doses, fewer than half have been administered. The country is going through a new wave of infection, registering this month the highest numbers of new cases and deaths since the beginning of the pandemic.

Still, the ministry published a revised rule this month limiting the program to influencers older than 60, though few could be found.

— Maria Varenikova

Dolores Hiwiller meeting with her daughters Karen King, right, and Sue Shirey in person for the first time since March of last year.
Dolores Hiwiller meeting with her daughters Karen King, right, and Sue Shirey in person for the first time since March of last year.Credit…Kristian Thacker for The New York Times

Every day for a year, Kathy James peered through the window at her mother’s assisted living facility outside Chicago and dreamed of the day they would be together again.

That moment finally came one recent morning, when Ms. James packed a goody bag full of family photographs, a Sunday copy of The Chicago Tribune and a container of potato soup, and met her mother, Renee Koerber, 90, inside the nursing home.

“I said, ‘Mom, we’re in the same room!'” said Ms. James, 63, her heart swelling with relief.

They had made it.

But sitting several feet apart in a common area, where they were not allowed to hug, Ms. James was also startled at how frail her mother looked. She seemed to grow tired after just 15 minutes. “I thought I would be so happy,” Ms. James said. “And I just feel such grief because of the year of time I have lost and I will never get back.”

Many American nursing homes have begun to welcome visitors again after a year of excruciating lockdowns. The Biden administration in March published sweeping guidelines allowing indoor visits in most cases. It is a profound change that comes as vaccinations ramp up, reaching nearly 100 million Americans, including a majority of people in nursing homes.

Even as the head of the Centers for Disease Control and Prevention warned this week of a possible fourth coronavirus surge, nursing homes are so far holding steady, reporting drastically fewer cases and deaths since the start of vaccinations. The improved outlook means that across the country, people are once again greeting loved ones in nursing homes with bouquets of flowers, with homemade pudding and lemon bars, with news from children and grandchildren.

Nursing homes have been centers of the pandemic since the beginning, when an outbreak was first identified at a facility outside Seattle. In the United States, the pandemic has killed more than 179,000 residents and employees of long-term care facilities — one-third of all coronavirus deaths nationwide — and left many others withering in isolation.

In reopening to visitors, nursing homes now offer an early glimpse at what everyone may face in trying to go back to normal after a year of separation and stillness. Some reunions may be tinged with grief, others with reminders of all that has changed.

Pauline Boss, a family therapist and professor emeritus at the University of Minnesota, said the experiences of families coming back together reminded her of research she had done on husbands returning home to wives after war, or cancer patients who suddenly learn they are in remission.

“Things don’t quite get back to normal,” Dr. Boss said.

Plaza de Armas in downtown Santiago, Chile, on Sunday after a quarantine order was imposed.
Plaza de Armas in downtown Santiago, Chile, on Sunday after a quarantine order was imposed.Credit…Cristobal Olivares for The New York Times

SANTIAGO, Chile — Having negotiated early access to tens of millions of doses of Covid-19 vaccines, Chile has been inoculating its residents faster than any other country in the Americas and appears poised to be among the first in the world to reach herd immunity.

But experts say the country’s speedy and efficient vaccination drive — only Israel, the United Arab Emirates and Seychelles have vaccinated a larger share of their populations — gave Chileans a more lax outlook toward the virus, contributing to a sharp spike in new infections and deaths.

The surge in cases, even as more than a third of Chile’s population has received at least the first dose of a Covid-19 vaccine, serves as a cautionary tale for other nations looking to vaccination drives to quickly put an end to the era of beleaguered economies, closed borders and social distancing. The rise in cases prompted a new set of strict lockdown measures that have restricted mobility for much of the country, affecting nearly 14 million people.

The severity of the crisis became clear on Sunday, as President Sebastian Pinera asked Congress to delay by six weeks a vote scheduled for early April to elect the representatives who will draft a new constitution and other officials. In a statement, Mr. Pinera argued that the current state of the pandemic was not conducive to holding a vote that was “democratic, inclusive and safe.”

While more than six million of the country’s 18 million people have been vaccinated, a surge in infections has left intensive care units operating with few beds to spare and the system at a breaking point.

Last week Chile recorded 7,626 new Covid-19 cases in a single day, a record, and the pace of new infections has doubled in the past month. Officials have also identified cases of new variants that were first seen in Britain and Brazil.

“No one questions that the vaccination campaign is a success story,” said Dr. Francisca Crispi, a regional president of Chile’s medical association. “But it conveyed a false sense of security to people, who felt that since we’re all being vaccinated the pandemic is over.”

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