U.S. Case Numbers Fall, but the Threat of Variants Is Growing

Here’s what you need to know: Genomic sequencing can detect and track virus variants, but the United States is sequencing relatively few coronavirus test samples. Lab technicians at Duke University prepared samples for sequencing earlier this month.Credit...Pete Kiehart for The New York Times As Americans anxiously watch the spread of coronavirus variants that were first identified in Britain and South Africa, scientists are finding a number of new variants that seem to have originated in the United States — and many of them may pose the same kind of extra-contagious threat. In a study posted on Sunday, a team of researchers reported seven growing lineages of the coronavirus, spotted in states across the country. All of them have evolved a mutation in the same genetic letter. “There’s clearly something going on with this mutation,” said Jeremy Kamil, a virologist at Louisiana State University Health Sciences Center and a co-author of the new study. It’s not clear yet whether this shared mutation makes the variants more contagious, but because it appears in a gene that influences how the virus enters human cells, the scientists are highly suspicious. “I think there’s a clear signature of an evolutionary benefit,” Dr. Kamil said. It’s not unusual for different genetic lineages to independently evolve in the same direction. Charles Darwin recognized convergent evolution in animals. Virologists have found that it happens with viruses, too. As the coronavirus branches into new variants, researchers are observing Darwin’s theory of evolution in action every day. It’s difficult to answer even basic questions about how prevalent the new variants are in the United States because the country sequences genomes from less than 1 percent of coronavirus test samples. The researchers found examples scattered across much of the country, but they can’t tell where they first arose. It’s also hard to say whether the variants are spreading now because they are more contagious, or for some other reason, like holiday travel or superspreader events. Scientists say the mutation could plausibly affect how easily the virus gets into human cells. But Jason McLellan, a structural biologist at the University of Texas at Austin who was not involved in the study, cautioned that the way that the coronavirus unleashes its harpoons was still fairly mysterious. “It’s tough to know what these substitutions are doing,” he said of the mutations. “It really needs to be followed up with some additional experimental data.” United States › United StatesOn Feb. 13 14-day change New cases 84,727 –37% New deaths 3,373* –16% *Includes many deaths from unspecified days World › WorldOn Feb. 13 14-day change New cases 344,564 –28% New deaths 10,713 –16% U.S. vaccinations › Fully vaccinated4.2% At least one dose12% Other trackers: Positive coronavirus samples being sequenced at Duke University in Durham, N.C., this month to determine which variants are circulating in the community.Credit...Pete Kiehart for The New York Times Vaccinations are picking up pace. The spread of the coronavirus in the United States has slowed drastically. The Centers for Disease Control and Prevention is urging K-12 schools to reopen safely and as soon as possible. But just as states are again lifting mask-wearing mandates and loosening restrictions, experts fear that more contagious variants could undo all that progress. That threat seems only to grow as researchers learn more. British government scientists now believe the more contagious variant that is ravaging Britain is also “likely” to be deadlier than earlier versions of the virus, according to a document posted on a government website on Friday. An earlier assessment on a smaller scale warned last month that there was a “realistic possibility” the variant was more lethal. The variant, also known as B.1.1.7, is spreading rapidly in the United States, doubling roughly every 10 days, another recent study found. In line with an earlier warning from the C.D.C., the study predicted that by March the variant could become the dominant source of coronavirus infection in the United States, potentially bringing a surge of new cases and increased risk of death. Beyond that, scientists reported on Sunday that they have begun to spot more new variants that seem to have emerged in the U.S. and are concerned that they may spread more readily than earlier versions. Vaccine distribution is accelerating — the U.S. is now averaging about 1.66 million doses a day, well above the Biden administration’s target of 1.5 million — but B.1.1.7 has a worrisome mutation that could make it harder to control with vaccines, a Public Health England study found this month. The variant has spread to at least 82 countries, and is being transmitted 35 percent to 45 percent more easily than other variants in the United States, scientists recently estimated. Most people wh

U.S. Case Numbers Fall, but the Threat of Variants Is Growing
Here’s what you need to know: Genomic sequencing can detect and track virus variants, but the United States is sequencing relatively few coronavirus test samples. Lab technicians at Duke University prepared samples for sequencing earlier this month.Credit...Pete Kiehart for The New York Times As Americans anxiously watch the spread of coronavirus variants that were first identified in Britain and South Africa, scientists are finding a number of new variants that seem to have originated in the United States — and many of them may pose the same kind of extra-contagious threat. In a study posted on Sunday, a team of researchers reported seven growing lineages of the coronavirus, spotted in states across the country. All of them have evolved a mutation in the same genetic letter. “There’s clearly something going on with this mutation,” said Jeremy Kamil, a virologist at Louisiana State University Health Sciences Center and a co-author of the new study. It’s not clear yet whether this shared mutation makes the variants more contagious, but because it appears in a gene that influences how the virus enters human cells, the scientists are highly suspicious. “I think there’s a clear signature of an evolutionary benefit,” Dr. Kamil said. It’s not unusual for different genetic lineages to independently evolve in the same direction. Charles Darwin recognized convergent evolution in animals. Virologists have found that it happens with viruses, too. As the coronavirus branches into new variants, researchers are observing Darwin’s theory of evolution in action every day. It’s difficult to answer even basic questions about how prevalent the new variants are in the United States because the country sequences genomes from less than 1 percent of coronavirus test samples. The researchers found examples scattered across much of the country, but they can’t tell where they first arose. It’s also hard to say whether the variants are spreading now because they are more contagious, or for some other reason, like holiday travel or superspreader events. Scientists say the mutation could plausibly affect how easily the virus gets into human cells. But Jason McLellan, a structural biologist at the University of Texas at Austin who was not involved in the study, cautioned that the way that the coronavirus unleashes its harpoons was still fairly mysterious. “It’s tough to know what these substitutions are doing,” he said of the mutations. “It really needs to be followed up with some additional experimental data.” United States › United StatesOn Feb. 13 14-day change New cases 84,727 –37% New deaths 3,373* –16% *Includes many deaths from unspecified days World › WorldOn Feb. 13 14-day change New cases 344,564 –28% New deaths 10,713 –16% U.S. vaccinations › Fully vaccinated4.2% At least one dose12% Other trackers: Positive coronavirus samples being sequenced at Duke University in Durham, N.C., this month to determine which variants are circulating in the community.Credit...Pete Kiehart for The New York Times Vaccinations are picking up pace. The spread of the coronavirus in the United States has slowed drastically. The Centers for Disease Control and Prevention is urging K-12 schools to reopen safely and as soon as possible. But just as states are again lifting mask-wearing mandates and loosening restrictions, experts fear that more contagious variants could undo all that progress. That threat seems only to grow as researchers learn more. British government scientists now believe the more contagious variant that is ravaging Britain is also “likely” to be deadlier than earlier versions of the virus, according to a document posted on a government website on Friday. An earlier assessment on a smaller scale warned last month that there was a “realistic possibility” the variant was more lethal. The variant, also known as B.1.1.7, is spreading rapidly in the United States, doubling roughly every 10 days, another recent study found. In line with an earlier warning from the C.D.C., the study predicted that by March the variant could become the dominant source of coronavirus infection in the United States, potentially bringing a surge of new cases and increased risk of death. Beyond that, scientists reported on Sunday that they have begun to spot more new variants that seem to have emerged in the U.S. and are concerned that they may spread more readily than earlier versions. Vaccine distribution is accelerating — the U.S. is now averaging about 1.66 million doses a day, well above the Biden administration’s target of 1.5 million — but B.1.1.7 has a worrisome mutation that could make it harder to control with vaccines, a Public Health England study found this month. The variant has spread to at least 82 countries, and is being transmitted 35 percent to 45 percent more easily than other variants in the United States, scientists recently estimated. Most people who catch the virus in Britain these days are being infected by that variant. The British research on B.1.1.7’s lethality did come with caveats, and the reasons for the variant’s apparently elevated death rate are not entirely clear. Some evidence suggests that people infected with the variant may have higher viral loads, a feature that could not only make the virus more contagious but also potentially undermine the effectiveness of certain treatments. But government scientists were relying on studies that examined a small proportion of overall deaths. They also struggled to account for the presence of underlying illnesses in people infected with the new variant, and for whether the cases originated in nursing homes. Bill Hanage, an epidemiologist at Harvard University, said that although “we do need to have a degree of caution” in looking at the findings, “it’s perfectly reasonable to think that this is something serious — I am certainly taking it seriously.” “It’s pretty clear we have something which is both more transmissible and is more worrying if people become infected,” he said. Angela Rasmussen, a virologist at Georgetown University, said relaxing restrictions now would be “courting disaster.” She urged Americans to “be extra vigilant” about mask wearing, distancing and avoiding enclosed spaces. “You don’t want to get any variant,” Dr. Rasmussen said, “but you really don’t want to get B.1.1.7.” The United States confirmed its first case of the B.1.1.7 variant on Dec. 29. Unlike Britain, it has been conducting little of the genomic sequencing necessary to track the spread of new variants that have caused concern, though the Biden administration has vowed to do more. On Friday, for the fifth time in six days, the number of new virus cases reported in the United States dipped below 100,000 — far less than the country’s peak of more than 300,000 reported on Jan. 8. As the number of virus cases and hospitalizations has fallen, the Republican governors of Montana, Iowa, North Dakota and Mississippi have recently ended statewide mask-wearing mandates. In New York, Gov. Andrew M. Cuomo, a Democrat, has allowed indoor dining to resume at 25 percent capacity, though experts have repeatedly warned that maskless activities, such as eating, in enclosed spaces are high-risk. Although virus case numbers are moving in the right direction, the loosening of restrictions has unnerved experts like Saskia Popescu, an epidemiologist at George Mason University in Virginia. “Now more than ever, with novel variants, we need to be strategic with these reopening efforts and be slow and not rush things,” she said. Video transcript Back bars 0:00/1:11 -0:00 transcript Lebanon Begins Coronavirus Vaccinations Lebanon started a nationwide drive to inoculate its citizens against Covid-19 on Sunday, after the country received its first round of 28,500 doses of the Pfizer-BioNTech vaccine. “It’s a very important day for us, we’ve been waiting for it, this pandemic took a great toll. We’ve had a lot of cases, a lot of fatalities in Lebanon. So we’re really looking forward to the vaccine to hopefully see some light at the end of the tunnel.” Privileged. Excited. Happy that this is happening, that it is happening to Lebanon. A good thing for once. It’s working. And I look forward to everybody being able to get the chance to get it too.” Lebanon started a nationwide drive to inoculate its citizens against Covid-19 on Sunday, after the country received its first round of 28,500 doses of the Pfizer-BioNTech vaccine.CreditCredit...Bilal Hussein/Associated PressBEIRUT, Lebanon — Lebanon began vaccinating its citizens against Covid-19 on Sunday, offering a rare glimmer of hope in a country suffering badly from several overlapping crises, just one of which is the pandemic. The first shot was administered to the director of the intensive care unit at the lead government hospital fighting the pandemic. The second was given to a famous 93-year-old comedian. The vaccination drive began after Lebanon received its first batch of 28,500 doses of the Pfizer-BioNTech vaccine. Using $34 million in financing from the World Bank, Lebanon is buying enough doses to vaccinate about two million people, roughly one-third of its population. Millions more doses are expected to arrive in the spring and summer through a United Nations program and commercial sources. Lebanon’s worst coronavirus surge peaked in mid-January, when the country was averaging more than 4,800 newly reported cases a day, according to a New York Times database; the average has since fallen somewhat, to about 2,700 a day. Some 337,000 people in Lebanon — almost 5 percent of the population — are now known to have had the virus, and more than 3,900 have died. To try to drive the numbers down, the government imposed a very strict lockdown in mid-January, with a 24-hour curfew and widespread shop closures. It eased the restrictions slightly last week, but the curfew largely remains in effect. The suffering caused by the pandemic has been compounded by a political crisis that has left Lebanon without an effective government for six months, and a financial crisis that has drastically weakened the local currency, making imported medicines, food and other products more expensive. A huge explosion in the port of Beirut last August also made matters worse, heavily damaging four hospitals, killing 200 people and leaving thousands more wounded. Video Prime Minister Jacinda Ardern of New Zealand announced on Sunday that Auckland would go into a three-day lockdown due to three unexplained positive coronavirus test results in a single family.CreditCredit...Gilles Martin-Raget/Agence France-Presse — Getty ImagesAUCKLAND, New Zealand — Faced with the creeping threat of more infectious coronavirus variants, Australia and New Zealand have responded to a small number of cases with near-immediate regional lockdowns. On Sunday night, as couples celebrating Valentine’s Day strolled arm-in-arm through central Auckland, Prime Minister Jacinda Ardern of New Zealand announced that the city would begin a three-day lockdown at midnight because of three unexplained positive test results in a single family. The rest of New Zealand would be subject to increased physical distancing requirements over the same period, she said. New Zealand has had almost no virus-related restrictions since the fall, when it successfully eliminated the virus for a second time. Overall, the country has reported 2,330 coronavirus cases and 25 deaths, far fewer in proportion to its population than most other developed nations. The Australian state of Victoria has also been placed in a short-term lockdown in response to a small outbreak, which began at a quarantine hotel and has grown to 16 cases. During the lockdown, which began at 11:59 p.m. Friday and is intended to last five days, most of Victoria’s six million people are not allowed to leave home except for limited periods of outdoor exercise or shopping. Professional tennis players who are in Melbourne, the state capital, for the Australian Open are considered “essential workers” and have been allowed to continue playing their matches, albeit without fans in attendance. Like New Zealand, Australia has had relatively few infections and deaths, and acts aggressively at the first sign of new outbreaks. Similar snap lockdowns in the Australian cities of Perth and Brisbane were successful recently at quashing transmission. Announcing the Auckland lockdown on Sunday, Ms. Ardern said, “Our view is, you’ll have less regret if you move early and hard than if you leave it and it gets out of control.” Residents of Good Shepherd nursing home in Wheeling, W.Va., participating in a penny auction last Monday. Credit...Amr Alfiky/The New York Times WHEELING, W.Va. — After nearly a year in lockdown for the residents of Good Shepherd Nursing Home — eating meals in their rooms, playing bingo through their television sets and isolating themselves almost entirely from the outside world — their coronavirus vaccinations were finished and the hallways were slowly beginning to reawaken. In a first, tentative glimpse at what the other side of the pandemic might look like, Betty Lou Leech, 97, arrived to the dining room early, a mask on her face, her hair freshly curled. “I’m too excited to eat,” she said, sitting at her favorite table once again. It has been a tragic year for nursing homes in America. More than 163,000 residents and employees of long-term care facilities have died from the coronavirus, about one-third of all virus deaths in the United States. Infections have swept through some 31,000 facilities, and nearly all have had to shut down in some way. For more than a million residents of nursing homes, the lockdowns themselves have been devastating. Cut off from family and largely confined to their rooms, many residents lost weight and saw ailments worsen. Some grew increasingly confused. Others sank into depression and despair. West Virginia has emerged as one of the first states to finish giving two doses of vaccines to the thousands of people inside its nursing homes, so Good Shepherd, a 192-bed Catholic home in Wheeling, was among the first facilities in the country to begin tiptoeing back toward normalcy last week. Good Shepherd locked down in March, even before the virus was found in West Virginia. Residents went without visits with loved ones, outings to the movies, even fresh air. Twice, the nursing home tried loosening restrictions, only to lock down again. An outbreak in November claimed the lives of five residents.Fifteen others got sick during the outbreak, including Ms. Leech. After recovering in the nursing home’s Covid-19 ward, she was feeling better, she said, and eager to return to some version of normal life. But even with the vaccinations completed, everything has not gone back to normal. Residents are allowed to socialize together again, but they are also asked to continue wearing masks. They sit several feet apart. And most relatives and friends still cannot come to visit. The continuing precautions offer insights into the complications of reopening, far beyond nursing homes. About 20 percent of people at Good Shepherd — mostly staff members and a few residents — declined to be vaccinated, reflecting a hesitance that has emerged across the country. Cases in the surrounding county remain high. More research is needed to understand whether vaccinated people might still be able to transmit the virus. People getting vaccinated this month at Castle Hill Community Center in New York. About 10 percent of people in the state have received their first dose.Credit...James Estrin/The New York Times New Yorkers with chronic health conditions that made them newly eligible for the Covid-19 vaccine flooded a state website and call center Sunday morning, leaving many unable to immediately schedule appointments at mass vaccination centers. State officials said on Sunday that 73,000 appointments had been scheduled as of 11:30 a.m., while 500,000 people went through an online eligibility screening tool needed to make appointments. Thousands were in virtual waiting rooms that can hold up to 8,000 people per vaccination site. Once those waiting rooms are full, people attempting to schedule appointments are told to try again later. Richard Azzopardi, a senior adviser to Gov. Andrew M. Cuomo, said demand was high, but “our infrastructure has remained up and intact.” He said that the state’s ability to make appointments depended on the vaccine supply, which is steadily increasing. Officials said the new criteria, which include chronic health conditions like obesity and hypertension, made four million more New Yorkers eligible for the Covid-19 vaccine. They join a growing number of people in the state who are eligible for the vaccine despite a shortage in supply. Those who are now eligible include adults who have certain health conditions that may increase their risk of severe illness or death from the coronavirus. Aside from obesity and hypertension, other conditions that would qualify New Yorkers for the vaccine include pulmonary diseases and cancer, Mr. Cuomo announced this month. He also made pregnancy a qualifying condition. Appointments for people who are in this group can be scheduled for as early as Monday, though most people will probably face a long wait because vaccine doses are scarce now. New Yorkers must provide proof of their condition with a doctor’s note, signed certification or medical documentation, Mr. Cuomo said. “While this is a great step forward in ensuring the most vulnerable among us have access to this lifesaving vaccine, it’s no secret that any time you’re dealing with a resource this scarce, there are going to be attempts to commit fraud and game the systems,” Mr. Cuomo said in a statement. In New York State, about 10 percent of the population has received its first dose, according to data gathered by The New York Times. With the new criteria, about 11 million people are now eligible in the state, including people ages 65 and older, health care workers and teachers. New York City recently opened mass vaccination sites at Yankee Stadium in the Bronx and Citi Field in Queens to better reach communities hit hard by the virus. The state and federal government also announced last week that the Federal Emergency Management Agency would open vaccination sites at Medgar Evers College in Brooklyn and York College in Queens. To check on eligibility and schedule an appointment, New Yorkers can complete a prescreening on the state’s website. They can also call the state’s vaccination hotline at 1-833-NYS-4VAX (1-833-697-4829) for more information about vaccine appointments. Tevon James, 5, getting his temperature checked in December before heading into his kindergarten class at P.S. 316 Elijah G. Stroud Elementary School in the Crown Heights section of Brooklyn, N.Y.Credit...Anna Watts for The New York Times For Julie Zuckerman, an elementary school principal in Manhattan, the summer felt like one never-ending day filled with fear and confusion about New York City’s plan to resume in-person teaching. But in the months since classrooms opened in September, something has shifted. Teachers at the school, Public School 513 in Washington Heights, appear more at ease, and some say they would like to be in their classrooms even when the building closes because of coronavirus cases. Parents, too, seem more confident: About half of the students are in the building most days, up from less than one-third in September. Ms. Zuckerman expects that even more children will return this spring. “People have made their peace; they’re not in crisis in the same way,” she said. “I feel there’s a huge night-and-day difference between what was going on last spring and what’s happened this year.” New York’s push to reopen classrooms in the fall — it was the first big school district in the country to do so — was a risky, high-stakes experiment. The city has had its share of miscommunication, logistical stumbles and disruptions — especially when classrooms and school buildings have closed frequently because of virus cases. The city requires a school to shutter for up to 10 days if two unrelated positive cases are confirmed there. Individual classrooms close when one or more positive cases are detected. The number of closures has risen considerably over the past few weeks, as test positivity rates across the city have remained high and weekly in-school testing has increased. New Yorkers have struggled to cope with the frequent interruptions to learning — and to parents’ schedules. Even so, parents, teachers, principals and union leaders are finding reasons for optimism at the midpoint of the academic year. In-school virus transmission has been very low, and there is broad agreement that children have benefited from being in classrooms. “Having the kids here is so much better for them, for everyone,” Ms. Zuckerman said. The strength of the plan will be tested again when about 62,000 middle school students return to classrooms for the first time since November. New York offers a preview of what other big city districts in the U.S — most prominently Chicago, where more schools are set to open next month — can expect as they inch closer to reopening classrooms after almost a year of remote learning. Philaé Lachaux at her mother’s home in Viroflay, France.Credit...Dmitry Kostyukov for The New York Times Philaé Lachaux, a 22-year-old business student in France, dreamed of striking out on her own in the live music industry. But the pandemic led to the loss of her part-time job as a waitress, and sent her back to live at her family home. Now, struggling to envision a future after months of restrictions, Ms. Lachaux says that loneliness and despair seep in at night. “I look at the ceiling, I feel a lump in my throat,” she said. “I’ve never had so many suicidal thoughts.” With curfews, closures and lockdowns in Europe set to drag into the spring or even the summer, mental health professionals are growing increasingly alarmed about the deteriorating mental state of young people. Last in line for vaccines and with schools and universities shuttered, young adults have borne many of the sacrifices made largely to protect older people, who are more at risk from severe infections. Across the world, the young have lost economic opportunities, missed traditional milestones and forfeited relationships at a pivotal time for forming identity. “Many feel they’re paying the price not of the pandemic, but of the measures taken against the pandemic,” said Dr. Nicolas Franck, the head of a psychiatric network in Lyon, France. In a survey of 30,000 people that he conducted last spring, young people ranked the lowest in psychological well-being, he said. In Italy and in the Netherlands, some youth psychiatric wards have filled to record capacity. In France, professionals have urged the authorities to consider reopening schools to fight loneliness. And in Britain, some therapists said that they had counseled patients to break lockdown guidelines to cope. In the United States, a quarter of 18- to 24-year-olds said they had seriously considered suicide, one report said. In Latin America and the Caribbean, a survey conducted by UNICEF of 8,000 young people found that more than a quarter had experienced anxiety and 15 percent depression. “We are in the midst of a mental health pandemic, and I don’t think it’s treated with near enough respect,” said Arkadius Kyllendahl, a psychotherapist in London who has seen the number of younger clients double in recent months. If you are having thoughts of suicide, the following organizations can help. In Britain, call Papyrus at +44 800 068 4141 (9am to midnight), or message Young Minds: text YM to 85258. You can also find a list of additional resources on Mind.org. In France, call SOS Amitié at +33 9 72 39 40 50 (24/7) or Fil Santé Jeunes at +33 800 235 236 (9am to 11pm). Ameli has a list of additional resources. In Italy, call Telefono Amico at +39 2 2327 2327 (10 am to midnight) or Telefono Azzurro at +39 19696 (a webchat is also available). A plane carrying doses of the Pfizer coronavirus vaccine from Belgium arrived at Narita airport, near Tokyo, on Friday.Credit...Kyodo, via Reuters TOKYO — Japan issued its first approval for a vaccine against the coronavirus on Sunday, saying that it would use the Pfizer-BioNTech vaccine to begin inoculating frontline health care workers this week. Japan has been slower than the United States and Europe to authorize any coronavirus vaccines, but it has also had the luxury of time. Public health measures have successfully kept infection rates low, and the country of 126 million people has recorded fewer than 7,000 deaths since the pandemic began. Nevertheless, the start of vaccinations is an important development for Japan. As the number of daily new infections reached a peak of nearly 8,000 in early January, the country declared a state of emergency in Tokyo and other regions that has been extended until March 7 in part because of the appearance of new, more infectious coronavirus variants. The number of daily new infections has declined drastically since then, with the seven-day average under 2,000, according to a New York Times database. Officials plan to first vaccinate a select group of health care workers who will then administer the shots to other medical professionals. The vaccine will be rolled out to the elderly and high-risk populations by late spring, according to plans published by the health ministry. But Japan is unlikely to have its entire population vaccinated before it hosts the Olympic Games this summer, and it has said athletes and other attendees will not be required to be vaccinated beforehand. Matthew Burris, 9, watches his mother, Erica Jackson get her finger pricked for a COVID-19 antibody test during Shared Harvest Foundation and myCovidMD’s free testing in honor of Dr. Martin Luther King, Jr. at Southside Church of Christ in Los Angeles last month.Credit...Sarah Reingewirtz/The Orange County Register, via Associated Press Two officials at the Food and Drug Administration said on Saturday that they had erred by allowing manufacturers to sell Covid-19 antibody tests that had not been proved accurate, flooding the United States with unreliable blood tests early in the pandemic. The officials, Dr. Jeffrey Shuren and Dr. Timothy Stenzel, said in an essay published in The New England Journal of Medicine that the F.D.A.’s guidance on March 16, 2020, which allowed companies to sell tests without emergency use authorization, “was flawed.” Within two weeks of that guidance, 37 manufacturers told the F.D.A. that they were introducing the tests in the United States, a number that swelled to 164 by the end of April, the officials said. Many of those tests turned out to be inaccurate, and by May the F.D.A. demanded that companies submit data that proved that their tests were reliable or they could be banned. As of this month, the officials said, the F.D.A. had issued 15 warning letters regarding the tests, removed references to 225 tests from its website and issued “import alerts” regarding 88 companies, meaning their imported tests will receive additional scrutiny — and could be blocked — at the border. “Our experience with serology tests underscores the importance of authorizing medical products independently, on the basis of sound science, and not permitting market entry of tests without authorization,” they wrote in the essay, referring to the blood tests. “Knowing what we know now, we would not have permitted serology tests to be marketed without F.D.A. review and authorization, even within the limits we initially imposed.” Soon after the tests first appeared in the United States, scientists discovered that many were flawed, even as some government officials and employers were saying the tests could be crucial to easing restrictions imposed during the pandemic. One review, which was not peer-reviewed, found that of 14 tests on the market, only three gave consistently reliable results. Many others gave false positive results, signaling that someone had already been infected with the coronavirus and had a heightened level of protection when that was not the case. Even some of the most effective tests did not detect antibodies in 10 percent of people who actually had them. The F.D.A.’s website lists the antibody tests that have been given emergency authorization and provides information about the effectiveness of those tests. In the essay, Dr. Shuren and Dr. Stenzel acknowledged that, although the F.D.A. had been operating with “limited and evolving information” and that other factors led to the prevalence of the faulty tests, the March 16 policy was what had “allowed it to happen.” Those We’ve Lost Dr. David Katzenstein was a virologist and researcher at Stanford who focused on AIDS, especially in southern Africa.Credit...TeachAids This obituary is part of a series about people who have died in the coronavirus pandemic. Read about others here. Dr. David Katzenstein may have been a dreamer, “with sometimes brilliant and sometimes slightly off-the-wall ideas,” one colleague said recently. But from the beginning, in a biosphere spawning new undetected and unconstrained killers, he was no ivory-tower researcher regarding the world through a microscope. After medical school, he interned at the University of New Mexico, where his work with Indigenous peoples developed into an abiding commitment to help underserved populations prevent and deal with infectious diseases. For 35 years, as a virologist and clinician, he not only helped advance the prevention, diagnosis and treatment of H.I.V. and AIDS; he also made those techniques available to middle- and low-income patients in sub-Saharan Africa. Dr. Katzenstein, who was professor emeritus of infectious diseases and global health at Stanford Medicine in California, died on Jan. 25 in Harare, Zimbabwe. He was 69. The cause was Covid-19, his stepdaughter, Melissa Sanders-Self, said. “Imbued with a passionate belief in social justice, David Katzenstein had an outsized impact on the fight against H.I.V. in sub-Saharan Africa,” Dr. Lloyd Minor, dean of the Stanford University medical school, said in a statement. While at the University of California, the International Antiviral Society-USA said, Dr. Katzenstein established a relationship with the medical microbiology department at the University of Zimbabwe’s medical school and became “one of the first U.S.-based H.I.V. researchers to commit to working in this region of the world.” In 1989, he joined the Stanford faculty as a clinical assistant professor of infectious diseases and was named the associate medical director of Stanford’s AIDS Clinical Trial Unit, which conducted research, including clinical trials, into antiretroviral drugs that extended the lives of people with H.I.V. He focused on the challenges posed by resistance to antiviral H.I.V. drugs and was among the first researchers to publicize the problem in Africa. In Zimbabwe, he directed the Biomedical Research and Training Institute in Harare, where he trained clinical researchers and introduced modern diagnostic and monitoring techniques to community health programs.