The United States and Britain this week diverged further in their vaccination strategies as American scientists, health experts and federal officials questioned or dismissed recent decisions made by officials in the U.K.
Britain has been straying increasingly from the dosing regimens tested in late-stage clinical trials run by the pharmaceutical companies Pfizer, Moderna and AstraZeneca.
On Wednesday, British health officials announced that they would delay second doses of vaccines made by Pfizer and AstraZeneca to concentrate on giving more people first injections — an attempt to more widely distribute the partial protections afforded by a single shot.
The idea has gained proponents in both countries. But many have also spoken out against the deviations from typical procedure, made without public meetings or strong data to support them. Some experts — including Dr. Anthony S. Fauci, the top infectious disease expert in the United States — balked at the prospect of implementing the idea in the U.S., where vaccine rollouts have already been stymied by myriad logistical hurdles and a patchwork approach to prioritizing who gets the first shots.
Also, Britain has quietly updated its vaccination playbook to allow for a mix-and-match vaccine regimen. If a second dose of the vaccine a patient originally received isn’t available, or if the manufacturer of the first shot isn’t known, health officials said, another vaccine may be used for the second shot.
But it is far from certain that the vaccines are so interchangeable, several researchers warned.
Viewed as cavalier departures from scientifically backed guidance, experts said, these decisions could further erode public trust in vaccines at a time when deployment is crucial and a new and potentially more transmissible variant of the coronavirus continues to ricochet around the globe.
“Even the appearance of tinkering has negatives, in terms of people having trust in the process,” said Natalie Dean, a biostatistician at the University of Florida. “You can have a highly efficacious vaccine, but if you can’t get it to people, then it’s not going to give that protection.”
Delaying the second dose appears to have gained little traction in the upper echelons of the U.S. government. In a news conference on Wednesday, Moncef Slaoui, the scientific adviser for Operation Warp Speed — the federal effort to accelerate vaccine development and distribution — expressed skepticism about the idea.
“It’s very important, I think, to use the vaccine based on how you have studied it,” Dr. Slaoui said. “For me, the biggest concern if we were to extend the time period between the first and second dose, is what happens to persistence of protection.”
On Friday, Dr. Fauci told CNN that he would advise U.S. officials not to follow Britain’s lead in accelerating first injections at the expense of second shots.
“I would not be in favor of that,” Dr. Fauci said. “We’re going to keep doing what we’re doing.”
In November, more than half a million Americans came to Mexico — of those, almost 50,000 arrived at Mexico City’s airport, according to official figures, less than half the number of U.S. visitors who arrived in November last year, but a surge from the paltry 4,000 who came in April, when much of Mexico was shut down. Since then, numbers have steadily ticked up: From June to August, U.S. visitors in Mexico more than doubled.
It’s unclear how many are visiting and how many are permanently relocating — or even just taking advantage of the six-month tourist visa that Americans are granted on arrival. Some may be Mexicans who also have American passports and are visiting family.
But walking the streets of Mexico City’s hipster neighborhoods these days, it can sometimes seem like English has become the official language.
The surge in visitors, however, comes as Mexico City enters a critical phase of the pandemic; cases have increased, and hospitals are stretched so thin that many sick people are staying home. The U.S. Centers for Disease Control and Prevention have also advised Americans to avoid all travel to Mexico.
Mexico City’s health care system “is basically overwhelmed,” Xavier Tello, a Mexico City health policy analyst, said via WhatsApp message. “The worst is yet to come.”
In mid-December, the authorities escalated Mexico City’s alert system to the highest level, which requires an immediate shutdown of all but essential businesses. But the lockdown came weeks after numbers had already reached the critical level of contagion, according to the government’s own figures.
As in much of the world, the most affluent are often the least affected. In Roma Norte, on one street corner, working-class Mexicans lined up for hours to buy oxygen tanks for their relatives who were sick at home with Covid-19, while just blocks away well-off young people lined up for croissants.
Ben Chafin, a Republican state senator from Virginia, has died from a Covid-19-related illness, the State Senate’s Republican Caucus confirmed on Friday evening.
Mr. Chafin, 60, was first elected to Virginia’s Senate in 2014. Before his time as senator he served as a member of Virginia’s House of Delegates.
“Ben was deeply and wholeheartedly committed to the commonwealth, and especially to the people of Southwest Virginia,” said Thomas K. Norment, Jr., the state’s Senate Republican leader. “A community leader in Russell, Ben rose to prominence in the field of law, banking and agriculture long before his neighbors elected him to the General Assembly.”
Gov. Ralph Northam offered his condolences to Mr. Chafin’s family, and said in a statement that he “will always be grateful for his courageous vote to expand health care for people who need it.” In 2018, Mr. Chafin joined three other Republican state senators in voting for the state of Virginia to expand Medicaid, according to the Richmond-Times Dispatch.
“This is sad news, to begin a new year with the loss of a kind and gracious man,” Mr. Northam said. “May we all recommit to taking extra steps to care for one another.”
After days of record-setting coronavirus tallies in Tokyo, the city’s governor on Saturday asked Japan’s central government to declare a national state of emergency for the first time since April.
Tokyo’s governor, Yuriko Koike, met on Saturday afternoon with Yasutoshi Nishimura, Japan’s economic minister, to request that the government do so as part of a broader effort to urge residents to stay home as much as possible.
The request came as Tokyo reported that its medical system was coming under strain. The governors of Saitama, Chiba and Kanagawa, suburban regions outside Tokyo, joined Tokyo in making the request.
Mr. Nishimura said the government still needed to consult with experts before making a declaration, but acknowledged that the rapid growth in infections had led to a “severe situation.”
If a state of emergency is declared, it would not be a formal lockdown and would mostly depend on voluntary compliance by businesses and residents.
Japan has recorded a total of 238,012 Covid-19 cases and 3,514 deaths. Tokyo reported a record 1,337 new infections on Thursday, and the nation has reported a daily average of nearly 3,000 cases over the past week.
Japan has also detected cases of the more transmissible variant of the virus that first emerged in England, and it closed its borders to new foreign travelers late last month.
Public health experts have expressed concern as Japan added 100,000 new cases in less than six weeks, after taking nearly eight months to get to its first 100,000 cases. Deaths have also been rising rapidly, with the total number having doubled in the past two months.
“If we don’t do anything but keep economic and social activities, there is a possibility that we will have a rapid increase” in cases, Shigeru Omi, the chairman of the government’s coronavirus panel of experts, told reporters last week.
He said that residents were growing tired of avoiding the kinds of activities or close quarters where the virus can easily spread, and that clusters had been detected in “workplaces, restaurants, among foreigners and the elderly.”
Other developments across the world:
Brazil’s pandemic death toll — the world’s second-highest — was approaching 200,000 on Saturday. Only the United States has recorded more deaths, with nearly 350,000. Brazil has reported around 7.6 million cases, and Minas Gerais leads all Brazilian states in new ones, with a daily average of nearly 4,000 over the past week.
South Korea said on Saturday that it would extend until Jan. 17 restrictions in and around Seoul that have shuttered schools, gyms, karaoke rooms, bars and other high-risk facilities. Those restrictions are at the second-highest level of a five-tier system, in a country whose pandemic response was once held up as a model. The government said on Saturday that it would expand one of the restrictions — a ban on gatherings of more than four people — from Seoul to the entire country.
In the northern Chinese city of Shenyang, which reported seven cases on Friday, officials ramped up restrictions on Saturday by closing public spaces, limiting some residents from leaving their home district and ordering nonessential workers in some areas to stay home, the state-run Xinhua News Agency reported. Officials in Beijing, about 400 miles southwest of Shenyang, also said they had succeeded in taming a small outbreak, but warned that it could still spread beyond the district where it began.
JERUSALEM — More than 10 percent of Israel’s population has received a first dose of a coronavirus vaccine, a rate that has far outstripped the rest of the world and buoyed the battered domestic image of the country’s leader, Benjamin Netanyahu, at a critical juncture.
Israel’s campaign, which began Dec. 20, has distributed the vaccine to three times as much of its population as the second-fastest nation, the tiny Persian Gulf kingdom of Bahrain, according to figures compiled mostly from local government sources by Our World in Data.
By contrast, less than 1 percent of the population of the United States and only small fractions of the population in many European countries received a vaccine dose by the end of 2020, according to Our World in Data, though China, the United States and Britain have each distributed more doses overall.
“It’s quite an astonishing story,” said Prof. Ran Balicer, the chairman of the national advisory team of experts that is counseling the Israeli government on its Covid-19 response.
Israel’s heavily digitized, community-based health system — all citizens, by law, must register with one of the country’s four H.M.O.s — and its centralized government have proved adept at orchestrating a national inoculation campaign, according to Israeli health experts.
With a population of nine million, Israel’s relatively small size has played a role as well, said Professor Balicer, who is also the chief innovation officer for Clalit, the largest of the country’s four H.M.O.s. So far, the government’s inoculation campaign has not extended to Palestinians in the occupied West Bank and Gaza Strip.
An aggressive procurement effort helped set the stage.
The health minister, Yuli Edelstein, said in an interview on Friday that Israel had entered into negotiations with drugmakers as an “early bird,” and that the companies were interested in supplying Israel because of its H.M.O.s’ reputation for efficiency and gathering reliable data.
“We are leading the world race thanks to our early preparations,” he said.
Turkey slammed its doors to travelers from Britain on Friday, saying that it had found 15 infections with the new, more transmissible variant of the virus that first emerged in England. All were among recent arrivals from the United Kingdom.
Turkey’s health minister, Fahrettin Koca, issued a statement saying that the 15 people infected with the variant were in isolation and that their contacts were being traced and placed under quarantine. In countrywide checks, the statement said, the virus had not been detected in anyone other than travelers who arrived from Britain.
The finding brings the number of countries that have detected the variant to at least 33 since Britain announced finding it on Dec. 8, and the number of countries barring travelers arriving from Britain to more than 40. Some countries are also imposing restrictions on travelers, including U.S. citizens, who in recent weeks visited the countries where the variant has been detected.
The Philippines expanded restrictions on travelers from Britain and 18 other countries, adding the United States after a third state, Florida, reported an infection involving the variant. Many countries have already restricted travel from the United States because of its staggering number of infections — the most in the world.
California and Colorado have also found cases involving the variant. None of those infected in the United States had traveled recently, so the new strain is clearly circulating, though at unknown levels.
The variant, known as B.1.1.7., has not been known to lead to more severe cases of Covid-19, but its circulation is likely to portend more infections and more hospitalizations at a time when many countries are already battling surges in caseloads and anticipating more from holiday gatherings and travel.
The list of countries that have identified infections with the variant has been growing rapidly, and as of Friday includes — besides the United States, Britain and Turkey — Australia, Belgium, Brazil, Canada, Chile, China, Denmark, Finland, France, Germany, Iceland, India, Ireland, Israel, Italy, Japan, Jordan, Lebanon, Malta, the Netherlands, Norway, Pakistan, Portugal, Singapore, South Korea, Spain, Sweden, Switzerland and the United Arab Emirates, as well as Taiwan, a self-governing democracy that Beijing claims as part of a unified China.
In South Africa, a similar version of the virus has emerged, sharing one of the mutations seen in B.1.1.7., according to scientists who detected it. That variant, known as 501.V2, has been found in up to 90 percent of the samples whose genetic sequences have been analyzed in South Africa since mid-November.
The British authorities said they have detected two cases of the variant identified in South Africa. In both cases, the infected people had been in contact with people who had traveled to Britain from South Africa in recent weeks. Switzerland, Finland, Australia, Zambia and France have also detected the variant.
And on Dec. 24, the head of the Africa Centers for Disease Control and Prevention, John Nkengasong, announced the discovery of yet another variant, this one in Nigeria, called B.1.207.
A more contagious form of the coronavirus is churning in the United States.
First identified in Britain, the variant already accounts for more than 60 percent of new coronavirus cases in London and its neighboring areas, and there’s worry the variant could further exacerbate cases in the U.S. and place greater strain on an already strained health care system.
A variant that spreads more easily also means that people will need to religiously adhere to precautions like social distancing, mask-wearing, hand hygiene and improved ventilation — unwelcome news to many Americans already chafing against restrictions.
We asked experts to weigh in on the evolving research into this new version of the coronavirus. Here’s what they had to say.
The new variant seems to spread more easily between people.
The new variant, known as B.1.1.7, seems to infect more people than earlier versions of the coronavirus, even when the environments are the same.
Scientists initially estimated that the new variant was 70 percent more transmissible, but a recent modeling study pegged that number at 56 percent. Once researchers sift through all the data, it’s possible that the variant will turn out to be just 10 to 20 percent more transmissible, said Trevor Bedford, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle.
Even so, Dr. Bedford said, it is likely to catch on rapidly and become the predominant form in the United States by March.
The variant behaves like earlier versions.
So far, at least, the variant does not seem to make people any sicker or lead to more deaths. Still, there is cause for concern: A variant that is more transmissible will increase the death toll simply because it will spread faster and infect more people.
The routes of transmission — by large and small droplets, and tiny aerosolized particles adrift in crowded indoor spaces — have not changed.
Infection with the new variant may increase the amount of virus in the body.
Some preliminary evidence from Britain suggests that people infected with the new variant tend to carry greater amounts of the virus in their noses and throats than those infected with previous versions.
That finding offers one possible explanation for why the new variant spreads more easily: The more virus that infected people harbor in their noses and throats, the more they expel into the air and onto surfaces when they breathe, talk, sing, cough or sneeze.
With previous versions of the virus, contact tracing suggested that about 10 percent of people who have close contact with an infected person — within six feet for at least 15 minutes — inhaled enough virus to become infected.
“With the variant, we might expect 15 percent of those,” Dr. Bedford said. “Currently risky activities become more risky.”
Scientists are still learning how the mutations have changed the virus.
Each infected person offers opportunities for the virus to mutate as it multiplies. With more than 83 million people infected worldwide, the coronavirus is amassing mutations faster than scientists expected at the start of the pandemic.
The vast majority of mutations provide no advantage to the virus and die out. But mutations that improve the virus’s fitness or transmissibility have a greater chance to catch on.
At least one of the 17 new mutations in the variant contributes to its greater contagiousness. The mechanism is not yet known. Some data suggest that the new variant may bind more tightly to a protein on the surface of human cells, allowing it to more readily infect them.
Muge Cevik, an infectious disease expert at the University of St. Andrews in Scotland and a scientific adviser to the British government, said it’s important to look at evidence “as preliminary and accumulating.”
But one thing is for sure, mitigation efforts will need to remain a priority.
“We need to be much more careful over all, and look at the gaps in our mitigation measures,” said Dr. Cevik said.
Alvin Kamara, the star running back for the New Orleans Saints and one of the best players in the N.F.L. this season, has been placed on the N.F.L.’s Covid-19 reserve list, a move that will keep him out of the team’s regular-season finale on Sunday and that may jeopardize his chances to appear in the team’s first game of the playoffs.
The league did not specify whether Kamara had tested positive or had come into contact with someone who had tested positive. But a person familiar with the league’s testing protocol said Kamara had indeed tested positive, which means he must isolate for at least 10 days and may return if he is asymptomatic at the end of that period.
The playoffs start next weekend, and Kamara’s availability would depend on when he gave the sample that tested positive — information that has not been made public.
However, the Saints (11-4) have a shot at getting a rest until the second weekend of the playoffs, when Kamara will be back unless he has Covid symptoms. To get that rest, they would have to end up as the top seed in their conference.
The Saints have already won the their division, the N.F.C. South, but are battling with the Green Bay Packers (12-3) and the Seattle Seahawks (11-4) for the No. 1 seed. Under a new playoff format introduced this season, only the top-seeded team will receive a bye in the first round of the playoffs.
To gain the bye, the Saints would have to win their game Sunday in Charlotte, N.C., against the Carolina Panthers (5-10), despite Kamara’s absence, and would also need the Packers to lose to the Chicago Bears (8-7) and the Seahawks to beat the San Francisco 49ers.
Kamara, 25, is coming off the best game of his four-year career, having rushed for six touchdowns on Christmas Day to tie a 91-year-old league record set by Ernie Nevers of the Chicago Cardinals in 1929.
This season, Kamara has rushed for a career-high 932 yards and a league-leading 16 touchdowns. He has also caught 83 passes for 756 yards and five touchdowns.
For months and months, life in Taiwan has been, in a word, normal. People have packed pro ball games, attended cello concerts and thronged night markets. Its Covid-19 death toll can be counted on two hands.
It is the kind of success that has created a sinking feeling in the stomachs of many residents: How much longer can the island’s good fortune last?
The high walls have kept the island from being deluged with infections, but they risk isolating Taiwan economically and politically if the rest of the world relaxes its defenses as vaccinations get underway.
For Chen Shih-chung, Taiwan’s health minister and head of its epidemic command center, success is all the more reason not to waver on the government’s strategy. The island has been sealed off to most visitors since March. People who are allowed to enter still have to quarantine under tight watch for two weeks.
The government is not likely to budge on those policies until there are vaccines that are a proven, lasting weapon against the virus, Mr. Chen said in an interview. Taiwan will not be like one of those places, he suggested, that eased lockdowns under public pressure only to have to tighten them again later.
Taiwan has already held fast to its entry restrictions and quarantines for much longer than many governments could without facing a big public backlash. The island’s economy has slowed along with the world’s during the pandemic but it continues to grow at a decent clip.
“It’s remarkable that Taiwan has held the line for so long,” said C. Jason Wang, an associate professor at Stanford University School of Medicine. But even if the island vaccinates its population by the middle of 2021, “then you’ve still got six months to go,” he said. “It’s really difficult to keep this up for another six months.”
“We came up with many of our policies when there were a few million infections around the world,” said Chan Chang-chuan, a professor at the College of Public Health at National Taiwan University. “But now there are tens of millions, and we’re heading toward a hundred million. It’s a whole different stage.”