Severe and critical cases of Covid-19 have hit record highs this week in the blockaded Gaza Strip, a development that health experts attributed to the proliferation of the highly transmissible coronavirus variant first identified in Britain.
Medical officials in the Hamas-run Health Ministry estimated that the variant now accounts for four out of five new cases in Gaza. They detected it in the densely populated territory for the first time in late March.
“We are in a dangerous place,” said Dr. Majdi Dhair, the director of the ministry’s preventive medicine department. “We expect more people to become infected and more people to enter hospitals. We ask God to pull us out of this situation.”
Over the past three weeks, severe cases — typically when a patient’s oxygen level falls to 94 percent or less — have risen to 219 from 58, according to ministry data. Critical cases, which can involve respiratory failure, septic shock or multiple organ dysfunction, jumped to 58 from 17.
On top of that, the ministry said on Monday that about 38 percent of the 4,700 virus test results it had received over the preceding 24 hours were positive — one of the highest rates in the past month.
Dr. Dhair said he believed that hospitals in Gaza were prepared to handle more severe and critical cases, but that they would probably have to postpone some surgical procedures to free up intensive care beds.
Devastated by years of conflict, Gaza’s hospitals were already dealing with challenging circumstances before the first cases of community transmission of the virus were discovered in the territory in August.
Gaza’s population is overwhelmingly young, and less than 1 percent of residents have been vaccinated so far.
The sharp rise in severe and critical cases has come just before the Muslim holy month of Ramadan, which begins on Tuesday. Traditionally during Ramadan, many Palestinians in Gaza would gather for large meals after sunset, pack streets in popular commercial districts and crowd into mosques for special evening prayers. But a number of those traditions will be prohibited this year because of the pandemic, the authorities said.
NEW DELHI — When the coronavirus first struck India last year, the country enforced one of the world’s strictest national lockdowns. The warning was clear: A fast spread in a population of 1.3 billion would be devastating.
Though damaging and ultimately flawed, the lockdown and other efforts appeared to work. Infections dropped and deaths remained low. Officials and the public dropped their guard. Experts warned fruitlessly that the government’s haphazard approach would bring a crisis when a new wave appeared.
Now the crisis is here.
India on Friday reported a daily record of 131,878 new infections as Covid-19 races out of control. Deaths, while still relatively low, are rising. Vaccinations, a mammoth task in such a large nation, are dangerously behind schedule. Hospital beds are running short.
Parts of the country are reinforcing lockdowns. Scientists are rushing to track new strains, including the more hazardous variants found in Britain and South Africa, that may be hastening the spread. But the authorities have declared contact tracing in some places to be simply impossible.
now behind the United States and Brazil.) The economic blowback of the resulting lockdown was devastating.
But the numbers at the time actually understated the first wave, scientists now say, and deaths in India never matched levels of the United States or Britain. Leaders began acting as if the problem had been solved.
Serum Institute of India, one of the world’s largest vaccine makers, boasted of a major stockpile of the Oxford-AstraZeneca vaccine, which makes up the bulk of the country’s drive. The government even launched a “vaccine diplomacy” campaign that sent doses to other countries.
But the initial rollout within India was slowed by complacency and plagued with public skepticism, including questions about the Oxford-AstraZeneca vaccine and lack of disclosure about an Indian-developed dose. Now the vaccination program is not matching the spread. The Serum Institute has said that practically all of its daily production of about two million doses will over the next two months go to the government, delaying commitments to other countries.
Several Indian states now worry that their vaccines stocks will run out. Mumbai, India’s largest city, had shut more than half of its vaccination centers, local media reported on Friday. The central government’s health minister lashed out at the states, reassuring that there would be no shortage and that more supplies were in the pipeline.
hit the campaign trail for state elections. Prime Minister Modi has addressed more than 20 rallies, each with thousands of often-unmasked people.
On Wednesday, Delhi officials said that even a solo car driver would be punished for not wearing a mask properly. The same day, Amit Shah, the country’s de facto No. 2 leader, drove through a campaign crowd in the state of West Bengal, waving without a mask and throwing rose petals.
The government also gave the go ahead for a long Hindu religious festival called Kumbh Mela, which runs through the end of April. Between one million to five million people attend the festival each day in the city of Hardiwar, on the banks of the river Ganges in the state of Uttarakhand.
no one would face restrictions as “the faith in God will overcome the fear of Covid-19.” Days later, Mr. Rawat tested positive for Covid.
The positivity rate of random tests is rising at the festival, and more than 300 participants have tested positive, said Dr. Arjun Singh Senger, a health officer at the festival.
The sheer speed of new infections has surprised health officials, who wonder whether variants might be a factor. Answering that question will be difficult. India has put only about 1 percent of its cases through genome sequencing tests, according to Dr. Reddy, of the Public Health Foundation of India, but researchers require a minimum of 5 percent to determine what is circulating.
So far, the government has found variants from the U.K. and South Africa as well as a local mutation. Limited information suggests that more infectious variants are circulating in India, as well, Dr. Reddy said.
Even if the variants have not yet been a major part of the new wave of infections, they have cast a shadow over India’s crucial vaccination drive. The AstraZeneca vaccine has been rejected by South Africa ineffective against that variant.
“This time, the speed is much faster than the last time,” said Dr. Vinod K. Paul, the head of India’s Covid response task force. “The next four weeks are very, very crucial for us.”
WASHINGTON — A highly infectious variant of the coronavirus that was first identified in Britain has become the most common source of new infections in the United States, the director of the Centers for Disease Control and Prevention said on Wednesday. The worrisome development comes as officials and scientists warn of a possible fourth surge of infections.
Federal health officials said in January that the B.1.1.7 variant, which began surging in Britain in December and has since slammed Europe, could become the dominant source of coronavirus infections in the United States, leading to a huge increase in cases and deaths.
At that point, new cases, hospitalizations and deaths were at an all-time high. From that peak, the numbers all declined until late February, according to a New York Times database. After several weeks at a plateau, new cases and hospitalizations are increasing again. The average number of new cases in the country has reached nearly 65,000 a day as of Tuesday, concentrated mostly in metro areas in Michigan as well as in the New York City region. That is an increase of 19 percent compared with the figure two weeks ago.
Dr. Rochelle Walensky, the C.D.C. director, who warned last week that she felt a recurring sense of “impending doom,” said on Wednesday that 52 of the agency’s 64 jurisdictions — which include states, some major cities and territories — are now reporting cases of these so-called “variants of concern,” including B.1.1.7.
60 percent more contagious and 67 percent more deadly than the original form of the coronavirus, according to the most recent estimates. The C.D.C. has also been tracking the spread of other variants, such as B.1.351, first found in South Africa, and P.1, which was first identified in Brazil.
The percentage of cases caused by variants is clearly increasing. Helix, a lab testing company, has tracked the relentless increase of B.1.1.7 since the beginning of the year. As of April 3, it estimated that the variant made up 58.9 percent of all new tests.
That variant has been found to be most prevalent in Michigan, Florida, Colorado, California, Minnesota and Massachusetts, according to the C.D.C. Until recently, the variant’s rise was somewhat camouflaged by falling infection rates over all, leading some political leaders to relax restrictions on indoor dining, social distancing and other measures.
against the warnings of some scientists.
Federal health officials are tracking reports of increasing cases associated with day care centers and youth sports, and hospitals are seeing more younger adults — people in their 30s and 40s who are admitted with “severe disease,” Dr. Walensky said.
It is difficult for scientists to say exactly how much of the current patterns of infection are because of the growing frequency of B.1.1.7.
“It’s muddled by the reopening that’s going on and changes in behavior,” said Dr. Adam Lauring, a virologist at the University of Michigan.
But he noted that people were becoming less cautious at a time when they should be raising their guard against a more contagious variant. “It’s worrisome,” he said.
At the same time, the United States is currently vaccinating an average of about three million people a day, and states have rushed to make all adults eligible. The C.D.C. reported on Tuesday that about 108.3 million people had received at least one dose of a Covid-19 vaccine, including about 64.4 million people who have been fully vaccinated. New Mexico, South Dakota, Rhode Island and Alaska are leading the states, with about 25 percent of their total populations fully vaccinated.
Scientists hope that vaccination will blunt any potential fourth surge.
On Tuesday, President Biden moved up his vaccination timetable by two weeks, calling states to make every American adult eligible by April 19. All states have already met or expect to beat this goal after he initially asked that they do so by May 1.
hundreds of genomes predicted that this variant could become predominant in the country in a month. At that time, the C.D.C. was struggling to sequence the new variants, which made it difficult to track them.
But those efforts have substantially improved in recent weeks and will continue to grow, in large part because of $1.75 billion in funds for genomic sequencing in the stimulus package that Mr. Biden signed into law last month. By contrast, Britain, which has a more centralized health care system, began a highly promoted sequencing program last year that allowed it to track the spread of the B.1.1.7 variant.
“We knew this was going to happen: This variant is a lot more transmissible, much more infectious than the parent strain, and that obviously has implications,” said Dr. Carlos del Rio, a professor of medicine and an infectious disease expert at Emory University. In addition to spreading more efficiently, he said, the B.1.1.7 strain appears to cause more severe disease, “so that gives you a double whammy.”
Perhaps even more troubling is the emergence of the virulent P.1 variant in North America. First identified in Brazil, it has become the dominant variant in that country, helping to drive its hospitals to the breaking point. In Canada, the P.1 variant emerged as a cluster in Ontario, then shut down the Whistler ski resort in British Columbia. On Wednesday, the National Hockey League’s Vancouver Canucks said at least 21 players and four staff members had been infected with the coronavirus.
“This is a stark reminder of how quickly the virus can spread and its serious impact, even among healthy, young athletes,” the team’s doctor, Jim Bovard, said in a statement.
Scientists have been predicting another rise in infections, as states relax their public health restrictions and restive Americans go back to school and work. But they are hoping that vaccination will blunt any potential fourth surge.
On Tuesday, President Biden moved up his vaccination timetable by two weeks, calling on states to make every American adult eligible for coronavirus vaccination by April 19, a goal nearly all states have already met or expect to beat after he initially asked they do so by May 1.
“It is in our power to minimize death, disease, and misery,” Andy Slavitt, a White House pandemic adviser, said Wednesday. “If all of us do our part, we can help save lives in April, May, and June. Wear a mask. Socially distance. Get vaccinated when it’s your turn.”
In February, a study that analyzed half a million coronavirus tests and hundreds of genomes predicted that in a month this variant could become predominant in the United States. At that time, the C.D.C. was struggling to sequence the new variants, which made it difficult to track them.
But those efforts have substantially improved in recent weeks and will continue to grow, in large part because of $1.75 billion in funds for genomic sequencing in the stimulus package that President Biden signed into law last month. By contrast, Britain, with a more centralized health care system, began a highly touted sequencing program last year that allowed it to track the spread of the B.1.1.7 variant.
“We knew this was going to happen, this variant is a lot more transmissible, much more infectious than the parent strain and that obviously has implications,” said Dr. Carlos del Rio, a professor of medicine and infectious disease expert at Emory University. In addition to spreading more efficiently, he said, the B.1.1.7 strain appears to cause more severe disease, “so that gives you a double whammy.”
The White House also announced an expansion to its vaccination program at community health centers, bringing the total to nearly 1,400 community centers across the country where people can get vaccinated. Mr. Slavitt said most of these community centers are in underserved neighborhoods with many uninsured patients. Last week, Mr. Biden promised that 90 percent of adults in the country will have a vaccine site within five miles of their home.
At the start of the year, Shay Fan felt relief: Vaccinations were on their way. Her relief turned to joy when her parents and in-laws got their shots.
Three months later, Ms. Fan, a 36-year-old freelance marketer and writer in Los Angeles, is still waiting for hers, and that joy is gone.
“I want to be patient,” she said.
But scrolling through Instagram and seeing photos of people, she said, “in Miami with no masks spraying Champagne into another person’s mouth,” while she sits in her apartment, having not had a haircut or been to a restaurant in more than a year, has made patience hard to practice. “It’s like when every friend is getting engaged before you, and you’re like, ‘Oh, I’m happy for them, but when is it my turn?’”
For much of the pandemic, the same rules applied: Stay at home, wear a mask, wash your hands.
But now, with vaccine distribution ramping up in some areas while others face a shortage, amid a third wave of coronavirus cases, or even warnings of a fourth, the rules are diverging around the world, and even within the same country.
and 47 percent of the population has had at least one vaccine dose. In New York, where at least 34 percent of people in the state have had at least one vaccine dose, there is talk about life feeling almost normal.
However, France, where only 14 percent of the population has received at least one vaccine dose, just entered its third lockdown. And Brazil, which has given at least one dose to 8 percent of the population, is reporting some of the world’s highest numbers of new cases and deaths per day. There are dozens of countries — including Japan, Afghanistan, Kenya, the Philippines — that have given only a single dose to less than 2 percent of their populations.
or racial lines. Older people, who make up the majority of those vaccinated, have been dining indoors, hugging grandchildren and throwing parties, while many younger people are still ineligible or repeatedly finding the “no appointments” message when they have tried to book.
Dr. Lynn Bufka, a psychologist and senior director at the American Psychological Association, said the pandemic has weighed heavily on teenagers, and a long wait for vaccines to be distributed to them could add to the stress.
“Children are in many ways those individuals whose lives have been disrupted as much as anyone but with less life experience on how to adapt to these kinds of disruptions,” Dr. Bufka said.
For American adults, at least, the fear of missing out should not last for much longer. President Biden has promised enough doses by the end of next month to immunize all of the nation’s roughly 260 million adults. In fact, the pace of vaccinations is quickening to such an extent that Biden administration officials anticipate the supply of coronavirus vaccines to outstrip demand by the middle of next month if not sooner.
Ms. Fan, the freelance writer and marketer in Los Angeles, will be eligible to book a vaccine appointment in mid-April. She does not plan to do anything wild — the basics are what she is looking forward to most. “I just need a haircut,” she said.
For weeks, the mood in much of the United States has been buoyant. Cases, hospitalizations and deaths from the coronavirus have fallen steeply from their highs, and millions of people are being newly vaccinated every day. Restaurants, shops and schools have reopened. Some states, like Texas and Florida, have abandoned precautions altogether.
In measurable ways, Americans are winning the war against the coronavirus. Powerful vaccines and an accelerating rollout all but guarantee an eventual return to normalcy — to backyard barbecues, summer camps and sleepovers.
But it is increasingly clear that the next few months will be painful. So-called variants are spreading, carrying mutations that make the coronavirus both more contagious and in some cases more deadly.
Even as vaccines were authorized late last year, illuminating a path to the pandemic’s end, variants were trouncing Britain, South Africa and Brazil. New variants have continued to pop up — in California one week, in New York and Oregon the next. As they take root, these new versions of the coronavirus threaten to postpone an end to the pandemic.
rising exponentially in the United States.
Limited genetic testing has turned up more than 12,500 cases, many in Florida and Michigan. As of March 13, the variant accounted for about 27 percent of new cases nationwide, up from just 1 percent in early February.
pledged a “down payment” of $200 million to ramp up surveillance, an infusion intended to make it possible to analyze 25,000 patient samples each week for virus variants. It’s an ambitious goal: The country was sequencing just a few hundred samples each week in December, then scaling up to about 9,000 per week as of March 27.
Until recently, B.1.1.7’s rise was camouflaged by falling rates of infection over all, lulling Americans into a false sense of security and leading to prematurely relaxed restrictions, researchers say.
“The best way to think about B.1.1.7 and other variants is to treat them as separate epidemics,” said Sebastian Funk, a professor of infectious disease dynamics at the London School of Hygiene and Tropical Medicine. “We’re really kind of obscuring the view by adding them all up to give an overall number of cases.”
Other variants identified in South Africa and Brazil, as well as some virus versions first seen in the United States, have been slower to spread. But they, too, are worrisome, because they contain a mutation that diminishes the vaccines’ effectiveness. Just this week, an outbreak of P.1, the variant that crushed Brazil, forced a shutdown of the Whistler Blackcomb ski resort in British Columbia.
as fast as possible.
Infections are rising again, driven to an uncertain degree by B.1.1.7 and other variants. Earlier this week, Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, pleaded with Americans to continue to practice masking and social distancing, saying she felt a sense of “impending doom.”
60 percent more contagious and 67 percent more deadly than the original form of the virus, according to the most recent estimates.
The variant is no different from the original in how it spreads, but infected people seem to carry more of the virus and for longer, said Katrina Lythgoe, an evolutionary biologist at the University of Oxford. “You’re more infectious for more days,” she said.
So contagious is B.1.1.7 that Britain succeeded in driving down infections only after nearly three months of strict stay-at-home orders, plus an aggressive vaccination program. Even so, cases fell much more slowly than they did during a similar lockdown in March and April.
three-quarters of new infections, some hospitals have had to move coronavirus patients to Belgium to free up beds. Roughly as many people are dying each day from Covid-19 in Europe as were this time a year ago.
For too long, government officials disregarded the threat. “Case plateaus can hide the emergence of new variants,” said Carl Pearson, a research fellow at the London School of Hygiene and Tropical Medicine. “And the higher those plateaus are, the worse the problem is.”
In the United States, coronavirus infections began a rapid decline in January, soon prompting many state leaders to reopen businesses and ease restrictions. But scientists repeatedly warned that the drop would not last. After the rate bottomed out at about 55,000 cases and 1,500 deaths per day in mid-March, some states — notably Michigan — began seeing an uptick.
Since then, the national numbers have steadily risen. As of Saturday, the daily count was up to nearly 69,000, and the weekly average was 19 percent higher than the figure two weeks earlier.
Pfizer-BioNTech and Moderna vaccines seem to be slightly less effective against B.1.351, the variant identified in South Africa. That variant contains the Eek mutation, which seems to enable the virus to partly sidestep the body’s immune response. The vaccines made by Johnson & Johnson, AstraZeneca and Novavax were even less potent against B.1.351.
“I think for the next year or two, E484K will be the most concerning” mutation, said Jesse Bloom, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle.
The mutation slightly alters the so-called spike protein sitting on the surface of the coronavirus, making it just a bit harder for antibodies to latch on and destroy the invader.
The good news is that the virus seems to have just a few survival tricks in its bag, and that makes it easier for scientists to find and block those defenses. “I’m feeling pretty good about the fact that there aren’t that many choices,” said Michel Nussenzweig, an immunologist at Rockefeller University in New York.
The Eek mutation seems to be the virus’s primary defense against the immune system. Researchers in South Africa recently reported that a new vaccine directed against B.1.351 ought to fend off all other variants, as well.
Pfizer, BioNTech and Moderna already are testing newly designed booster shots against B.1.351 that should work against any variants known to blunt the immune response.
Instead of a new vaccine against variants, however, it may be just as effective for Americans to receive a third dose of the Pfizer-BioNtech or Moderna vaccines in six months to a year, said Dr. Anthony S. Fauci, head of the National Institute of Allergy and Infectious Diseases.
That would keep antibody levels high in each recipient, overwhelming any variant — a more practical strategy than making a specialized vaccine for each new variant that emerges, he said.
“My only concern about chasing all the variants is that you’d almost be playing Whac-A-Mole, you know, because they’ll keep coming up and keep coming up,” Dr. Fauci said.
In one form or another, the new coronavirus is here to stay, many scientists believe. Multiple variants may be circulating in the country at the same time, as is the case for common cold coronaviruses and influenza. Keeping them at bay may require an annual shot, like the flu vaccine.
The best way to deter the emergence of dangerous variants is to keep cases down now and to immunize the vast majority of the world — not just the United States — as quickly as possible. If significant pockets of the globe remain unprotected, the virus will continue to evolve in dangerous new ways.
“This might be something that we have to deal with for a long time,” said Rosalind Eggo, an epidemiologist at London School of Hygiene and Tropical Medicine.
Still, she added, “Even if it changes again, which it is very likely to do, we are in a better, much stronger position than a year ago to deal with it.”
Americans who are fully vaccinated against Covid-19 can safely travel at home and abroad, as long as they take basic precautions like wearing masks, federal health officials announced on Friday, a long-awaited change from the dire government warnings that have kept many millions home for the past year.
In announcing the change at a White House news conference, officials from the Centers for Disease Control and Prevention stressed that they preferred that people avoid travel. But they said growing evidence of the real-world effectiveness of the vaccines — which have been given to more than 100 million Americans — suggested that inoculated people could do so “at low risk to themselves.”
The shift in the C.D.C.’s official stance comes at a moment of both hope and peril in the pandemic. The pace of vaccinations has been rapidly accelerating across the country, and the number of deaths has been declining.
Yet cases are increasing significantly in many states as new variants of the coronavirus spread through the country. Just last Monday, Dr. Rochelle P. Walensky, the C.D.C. director, warned of a potential fourth wave if states and cities continued to loosen public health restrictions, telling reporters that she had feelings of “impending doom.”
suggested such cases might be rare, but until that question is resolved, many public health officials feel it is unwise to tell vaccinated Americans simply to do as they please. They say it is important for all vaccinated people to continue to wear masks, practice social distancing and take other precautions.
Under the new C.D.C. guidance, fully vaccinated Americans who are traveling domestically do not need to be tested for the coronavirus or follow quarantine procedures at the destination or after returning home. When they travel abroad, they only need to get a coronavirus test or quarantine if the country they are going to requires it.
coronavirus test before boarding a flight back to the United States, and they should get tested again three to five days after their return.
The recommendation is predicated on the idea that vaccinated people may still become infected with the virus. The C.D.C. also cited a lack of vaccine coverage in other countries, and concern about the potential introduction and spread of new variants of the virus that are more prevalent overseas.
Most states have accelerated their timelines for opening vaccinations to all adults, as the pace of vaccinations across the country has been increasing. As of Friday, an average of nearly three million shots a day were being administered, according to data reported by the C.D.C.
The new advice adds to C.D.C. recommendations issued in early March saying that fully vaccinated people may gather in small groups in private settings without masks or social distancing, and may visit with unvaccinated individuals from a single household as long as they are at low risk for developing severe disease if infected with the virus.
Travel has already been increasing nationwide, as the weather warms and Americans grow fatigued with pandemic restrictions. Last Sunday was the busiest day at domestic airports since the pandemic began. According to the Transportation Security Administration, nearly 1.6 million people passed through the security checkpoints at American airports.
But the industry’s concerns are far from over. The pandemic has also shown businesses large and small that their employees can often be just as productive working remotely as in face-to-face meetings. As a result, the airline and hotel industries expect it will be years before lucrative corporate travel recovers to prepandemic levels, leaving a gaping hole in revenues.
And while leisure travel within the United States may be recovering steadily, airlines expect it will still take until 2023 or 2024 for passenger volumes to reach 2019 levels, according to Airlines for America, an industry group. The industry lost more than $35 billion last year and continues to lose tens of millions of dollars each day, the group said.
the country’s government said
The C.D.C. on Thursday also issued more detailed technical instructions for cruise lines, requiring them to take steps to develop vaccination strategies and make plans for routine testing of crew members and daily reporting of Covid-19 cases before they can run simulated trial runs of voyages with volunteers, before taking on real passengers. The C.D.C.’s directives acknowledge that taking cruises “will always pose some risk of Covid-19 transmission.”
Some destinations and cruise lines have already started requiring that travelers be fully vaccinated. The cruise line Royal Caribbean is requiring passengers and crew members 18 or older to be vaccinated in order to board its ships, as are Virgin Voyages, Crystal Cruises and others.
For the moment, airlines are not requiring vaccinations for travel. But the idea has been much talked about in the industry.
The Centers for Disease Control and Prevention on Thursday walked back controversial comments made by its director, Dr. Rochelle P. Walensky, suggesting that people who are vaccinated against the coronavirus never become infected or transmit the virus to others.
The assertion called into question the precautions that the agency had urged vaccinated people to take just last month, like wearing masks and gathering only under limited circumstances with unvaccinated people.
“Dr. Walensky spoke broadly during this interview,” an agency spokesman told The Times. “It’s possible that some people who are fully vaccinated could get Covid-19. The evidence isn’t clear whether they can spread the virus to others. We are continuing to evaluate the evidence.”
The agency was responding in part to criticism from scientists who noted that current research was far from sufficient to claim that vaccinated people cannot spread the virus.
MSNBC’s Rachel Maddow, Dr. Walensky referred to data published by the C.D.C. showing that one dose of the Moderna or Pfizer-BioNTech vaccine was 80 percent effective at preventing infection, and two doses were 90 percent effective.
That certainly suggested that transmission from vaccinated people might be unlikely, but Dr. Walensky’s comments hinted that protection was complete. “Our data from the C.D.C. today suggests that vaccinated people do not carry the virus, don’t get sick,” she said. “And that it’s not just in the clinical trials, it’s also in real-world data.”
Dr. Walensky went on to emphasize the importance of continuing to wear masks and maintain precautions, even for vaccinated people. Still, the brief comment was widely interpreted as saying that the vaccines offered complete protection against infection or transmission.
In a pandemic that regularly spawns scientific misunderstanding, experts said they were sympathetic to Dr. Walensky and her obvious desire for Americans to continue to take precautions. It was only Monday that she said rising caseloads had left her with a sense of “impending doom.”
“If Dr. Walensky had said most vaccinated people do not carry virus, we would not be having this discussion,” said John Moore, a virologist at Weill Cornell Medicine in New York.
“What we know is the vaccines are very substantially effective against infection — there’s more and more data on that — but nothing is 100 percent,” he added. “It is an important public health message that needs to be gotten right.”
Misinterpretation could disrupt the agency’s urgent pleas for immunization, some experts said. As of Wednesday, 30 percent of Americans had received at least one dose of a vaccine and 17 percent were fully immunized.
“There cannot be any daylight between what the research shows — really impressive but incomplete protection — and how it is described,” said Dr. Peter Bach, director of the Center for Health Policy and Outcomes at Memorial Sloan Kettering Cancer Center in New York.
“This opens the door to the skeptics who think the government is sugarcoating the science,” Dr. Bach said, “and completely undermines any remaining argument why people should keep wearing masks after being vaccinated.”
All of the coronavirus vaccines are spectacularly successful at preventing serious disease and death from Covid-19, but how well they prevent infection has been less clear.
Clinical trials of the vaccines were designed only to assess whether the vaccines prevent serious illness and death. The research from the C.D.C. on Monday brought the welcome conclusion that the vaccines are also extremely effective at preventing infection.
The study enrolled 3,950 health care workers, emergency responders and others at high risk of infection. The participants swabbed their noses each week and sent the samples in for testing, which allowed federal researchers to track all infections, symptomatic or not. Two weeks after vaccination, the vast majority of vaccinated people remained virus-free, the study found.
Follow-up data from clinical trials support that finding. In results released by Pfizer and BioNTech on Wednesday, for example, 77 people who received the vaccine had a coronavirus infection, compared with 850 people who got a placebo.
“Clearly, some vaccinated people do get infected,” Dr. Duprex said. “We’re stopping symptoms, we’re keeping people out of hospitals. But we’re not making them completely resistant to an infection.”
The number of vaccinated people who become infected is likely to be higher among those receiving vaccines made by Johnson & Johnson and AstraZeneca, which have a lower efficacy, experts said. (Still, those vaccines are worth taking, because they uniformly prevent serious illness and death.)
Infection rates may also be higher among people exposed to a virus variant that can sidestep the immune system.
Cases across the country are once again on the upswing, threatening a new surge. Dr. Walensky’s comment came just a day after she made an emotional appeal to the American public to continue taking precautions.
“I am asking you to just hold on a little longer, to get vaccinated when you can, so that all of those people that we all love will still be here when this pandemic ends,” she said.
Given the rising numbers, it’s especially important that immunized people continue to protect those who have not yet been immunized against the virus, experts said.
“Vaccinated people should not be throwing away their masks at this point,” Dr. Moore said. “This pandemic is not over.”
Declines in coronavirus testing in many states in the South and the Great Plains are making it harder to know just how widely the virus may be spreading in those states, even as restrictions are lifted and residents ease back into daily life, experts say.
States in both regions are reporting few new cases relative to their population, compared with harder-hit states like Michigan or New York. But they are also testing far fewer people.
Kansas, for example, is now testing about 60 people a day for every 100,000 in population, according to data compiled by Johns Hopkins University, and Alabama only a bit more. The picture is similar in Iowa, Mississippi and elsewhere.
By contrast, New York is averaging 1,200 tests a day per 100,000, and Rhode Island 1,677 per 100,000.
Testing has been falling in Kansas since Jan. 1, even though hospitalizations were at their highest level of the pandemic then, according to Tami Gurley, co-chair of the virus task force at the University of Kansas Medical Center. The state is now doing fewer tests relative to its population than any state except Idaho.
The tests they are doing in these low-rate states are finding virus.
Twelve percent of Kansas’ coronavirus tests are coming back positive. Alabama’s positivity rate is 12.8 percent. The rate in Idaho is 27.3 percent, highest in the country. In New York, it’s just 3.5 percent.
So in the states that are doing relatively little testing, it’s possible that their daily case counts are low in part because asymptomatic or mild-symptom cases are going undetected.
Ms. Gurley says she is closely following hospitalizations, as a better indicator of the spread of the virus than new-case reports.
“We think that people are more focused on getting vaccines than getting tested,” she said. “It certainly makes it harder to figure out where we are going. We feel like we are at the point of another uptick in cases.”
Many states in the South and Midwest have relaxed their restrictions, including mask mandates, even though the national data signals that another surge in cases may be coming, according to Edward Trapido, an epidemiologist and associate dean for research at the Louisiana State University School of Public Health.
And many states are shifting resources away from testing to boost vaccination efforts and meet President Biden’s goal of making all adult Americans eligible for a shot by May 1.
As a result, Dr. Trapido said, in many places these days, only the sickest patients are seeking out a coronavirus test.
“As vaccines have become widespread, people are becoming comfortable about not being tested,” he said. “There is a natural experiment going on. It’s a battle between getting people vaccinated and keeping the percent positive low. When I see a slight change in the curve upward, I get alarmed.”
Ms. Gurley said the shift in emphasis away from testing and toward vaccination may stem in part from widespread public fatigue with pandemic precautions and the political imperative in many states to reopen swiftly.
If all you want to do is prevent deaths from the virus, that may make sense, she said, but “if your end goal is to prevent spread, then we need more testing.”
The next major flash point over coronavirus response has already provoked cries of tyranny and discrimination in Britain, protests in Denmark, digital disinformation in the United States and geopolitical skirmishing within the European Union.
The subject of debate: vaccine passports — government-issued cards or smartphone badges stating that the bearer has been inoculated against the coronavirus.
The idea is to allow families to reunite, economies to restart and hundreds of millions of people who have received a shot to return to a degree of normalcy, all without spreading the virus. Some versions of the documentation might permit bearers to travel internationally. Others would allow entry to vaccinated-only spaces like gyms, concert venues and restaurants.
While such passports are still hypothetical in most places, Israel became the first to roll out its own last week, capitalizing on its high vaccination rate. Several European countries are considering following. President Biden has asked federal agencies to explore options. And some airlines and tourism-reliant industries and destinations expect to require them.
wrote in Scientific American. But with vaccines distributed unequally by race, class and nationality, “it is not obvious that they are ethical.”
Still, there are clear upsides: grandparents reuniting with out-of-town grandchildren; sports, concerts and other events partly but safely returning; resumption of international travel and some tourism; businesses reopened without putting workers at undue risk.
All of that is why, Drs. Hassoun and Herlitz wrote, vaccine documents “may be inevitable.”
Widening Society’s Divides
Some countries require proof of vaccination — for example, against yellow fever — to enter. So do schools and day-care facilities in many American states.
higher rates. In Western countries, those communities tend to be white and well-off.
This evokes an uncomfortable image: professional-class white people disproportionately allowed into shops, baseball games and restaurants, with people of color and members of the working classes disproportionately kept out. If workplaces require proof of vaccination, it could tilt employment as well.
“If vaccines become a passport to doing different things, we’re going to see the communities that have been already hardest hit by Covid being left behind,” said Nicole A. Errett, a University of Washington public health expert.
said that they hope to set a policy this summer for accepting vaccine passports.
urging governments to wait for international standards on the passports before opening up travel, lest uneven standards lead to unsafe practices or geopolitical gamesmanship.
“A challenge since the beginning has been getting countries to do what’s best for the world instead of what’s best for people inside of their borders,” Dr. Errett said.
Witness the maneuvering within the European Union, whose 27 countries share long borders but have starkly different economic needs and vaccination rates.
Southern European states like Spain and Greece, which rely on tourism, are pushing for the bloc to adopt the documents. German and French officials have expressed reservations, at least for now. Their countries have lower vaccination rates, meaning that travel restrictions would put their residents at a relative disadvantage.
A Struggle Over Mandates
When Britain’s foreign secretary speculated recently that proof of vaccination might be required for pubs and stores, a lawmaker in his own party, Mark Harper, retorted, “I don’t think you want to require people to have to have a particular medical procedure before they can go about their day-to-day life.”
California’s vaccine struggle, over whether to tighten school requirements after measles and whooping cough outbreaks highlighted the state’s low immunization rates, offers a worrying preview.
one-third of Americans, in one poll, predominantly Republicans — are merely hesitant. The push to achieve herd immunity will depend on that third.
A Muddled Mission
One problem: There is no agreement on the primary purpose of a vaccine passport program.
Governments typically talk about them as a way to open up economies. Individuals, as a way to re-enter normal life. Public health experts, as a way to reduce transmissions.
Those goals align, but imperfectly. At some point, the authorities have to prioritize.
Dr. Errett ticked through implementation questions, broadly unknown, that could force an answer. Would you need two doses to get the document or just one? Do Russian- or Chinese-made vaccines qualify? What are the rules for religious or medical opt-outs? Are some activities restricted to card-carriers until herd immunity, just until infections fall below a certain line — or forever?
“We need to be cognizant of the costs and benefits,” she said, and not just to adjust as we go, but for “the precedent we’re setting.”
“We pandemic people,” she said, “have been saying it since the beginning: We don’t expect this to be the last pandemic that we see.”
Matina Stevis-Gridneff contributed reporting from Brussels.