Dr. Fauci was the federal government’s top infectious disease expert for decades, and helped steer the U.S. response to Covid-19.Dr. Anthony S. Fauci, who served as the federal government’s top infectious disease specialist for nearly 40 years and played a key role in steering the United States through the coronavirus pandemic, will join the faculty of Georgetown University in Washington next month.Dr. Fauci, 82, retired from the National Institutes of Health last year, having served as the director of its National Institute of Allergy and Infectious Diseases since 1984. He was also the top Covid adviser to President Biden, a role he had filled under President Donald J. Trump. Georgetown announced his new job on Monday.Dr. Fauci will work at Georgetown’s School of Medicine and its McCourt School of Public Policy, the university said. A spokeswoman for Georgetown did not immediately respond to an inquiry seeking details about what courses he will teach. The university’s announcement said Dr. Fauci’s role at the School of Medicine will be in an infectious disease division focused on education, research and patient care.At the N.I.H., Dr. Fauci spent decades overseeing research on established infectious diseases — including H.I.V./AIDS, tuberculosis and malaria — and emerging ones like Ebola, Zika and Covid-19. He was also a principal architect of the President’s Emergency Plan for AIDS Relief, a program that has delivered lifesaving treatment to more than 20 million people in 54 countries since its inception 20 years ago under President George W. Bush.Dr. Fauci was already a high-profile public health official when the coronavirus pandemic hit in early 2020. But the race to understand and respond to the virus quickly thrust him to the forefront of American life. Through regular appearances at White House briefings, he became a larger-than-life personality counseling calm for an anxious nation.During an appearance at Georgetown University in 2014, Dr. Fauci, from left, spoke with Ron Klain, who at the time was coordinating the White House’s response to Ebola, and the university’s president, John DeGioia.Alex Wong/Getty ImagesHe was polarizing, too. Because his job frequently put him in the awkward position of publicly contradicting Mr. Trump, he became an enemy of the political right and a hero to the left.In an interview with The New York Times last year, Dr. Fauci said he was “completely nonpolitical” and “did not like nor seek out a position of having to publicly contradict a president of the United States.”“The far right seems to think I did that deliberately and took pleasure in it,” he said. “I did not.”When Dr. Fauci retired last year, he said that he hoped to do some public speaking, write a memoir, become affiliated with a university and treat patients if it had a medical center.As for the memoir, Dr. Fauci told The Times that he hoped to write a “real” one that told the story of his life, not just his turn in the national spotlight during the pandemic.“I would much rather give a story of the whole me, from the time I grew up in the streets of Brooklyn to where I am right now,” he said. “But I don’t know. I’ve never written a book before.”

Tainted syrup from India may be connected to the deaths of dozens of children in Gambia, officials said. Indonesia banned cough syrup sales, though the link there is unclear.Early this month, the World Health Organization’s director said that ingredients in four cold and cough syrups made in India may have been linked to acute kidney injuries and the deaths of 66 children in Gambia — and that the products may have been distributed to other countries.Days later, the authorities in India began an investigation and halted all production by the company that made the tainted medication.This week, the authorities in Indonesia banned the sale of all cough syrups nationwide. They are now investigating the deaths of nearly 100 children from acute kidney injuries this year. But so far, there is no proof of a connection to tainted medicine there, though contaminated cough syrups have been found in some of the children’s homes.Here’s what we know so far:Where did the tainted syrup come from?The four medicines linked to the deaths in Gambia were produced by Maiden Pharmaceuticals, a company based in New Delhi that exports medicines across the developing world.The W.H.O.’s director, Tedros Adhanom Ghebreyesus, told reporters on Oct. 5 that the agency was conducting an investigation. In a medical product alert issued the same day, the agency said that analysis of the four medicines had found “unacceptable” amounts of diethylene glycol and ethylene glycol, two industrial chemicals that are toxic to people and can cause serious injury or death in children. The next day, the health authorities in Gambia ordered a recall of the four tainted products.The police in Gambia later said that the deaths of 69 children from acute kidney injury were linked to the four cough syrups made by Maiden Pharmaceuticals.Last week, the authorities in India said they had suspended all manufacturing by the company after discovering violations at its factory in Haryana State, outside New Delhi. The state drug regulator said the tainted products sold in Gambia had been made at the Haryana factory in December 2021.The Indian government formed a committee to investigate the tainted drugs and the deaths in Gambia. Vivek Goyal, the director of Maiden Pharmaceuticals, has said that the company is cooperating with investigators.Are the Indonesia deaths related?At this point, there is no evidence of that.This week, the government of Indonesia banned all syrup-based medications, saying it was investigating the deaths of 99 children from fatal acute kidney injury. Health Minister Budi Gunadi Sadikin said on Thursday that cough syrups containing diethylene glycol and ethylene glycol had been found in some of the homes where children had died.But it was not clear how many of the deaths, if any, were connected to tainted syrup. A 2020 academic study said that while epidemiological data on acute kidney injury cases in Indonesia was limited, the condition was a common problem in intensive care units of the country’s hospitals.Penny K. Lukito, the head of Indonesia’s food and drug agency, said on Oct. 15 that no products made by Maiden Pharmaceuticals, including the four medicines linked to the Gambia deaths, were registered in Indonesia. It is very unlikely that an imported drug could be sold legally in Indonesia without being registered.India has said that Maiden’s tainted products were sent only to Gambia, but the W.H.O. has said that they may have been distributed to other countries.Why are these two chemicals so harmful?Diethylene glycol and ethylene glycol are clear, colorless and syrupy alcohols used for antifreeze and other industrial applications. Unlike the kind of alcohol that humans drink safely, they are potentially deadly even in small quantities.The effects of ingesting them can include headache, abdominal pain, vomiting, diarrhea and inability to urinate. The chemicals can also damage the liver, kidneys and central nervous system.The primary way that medical professionals treat people who have taken the chemicals is by giving them a drug, fomepizole, that prevents the body from metabolizing them, said Leo Schep, a toxicologist in New Zealand.“But you’ve got to get in early” to ward off severe complications, he added. “Otherwise you’re on a slippery slope.”There is precedent for scandals like these.Diethylene glycol has been used in the past as a cheap substitute for glycerin, a sweet syrup that is a safe ingredient in many over-the-counter drugs.That has sometimes led to mass poisonings. At least 84 children died in Nigeria in 2009 after taking a medicine for teething pain that contained diethylene glycol.In India, 33 children died in 1998 after taking a contaminated cough expectorant. Eight children also died that year after taking paracetemol syrup. Both of those products contained diethylene glycol.Could something this deadly happen in the United States?It’s unlikely.After contaminated drugs killed more than 100 people across the United States in 1937, Congress passed a law that increased the federal government’s ability to regulate drugs.Dr. Schep said that because of that law and other regulations, the risk of another mass poisoning from contaminated medicine in the United States is low. The same is true for Australia, New Zealand and the European Union because they all have similar laws, he added.Hari Kumar

A Canadian family is on a yearlong journey across Asia and Africa because three of their four children have an eye condition that causes blindness.For their youngest son’s fifth birthday this summer, Edith Lemay and her husband took their children on a hot-air balloon ride above central Turkey that began before dawn.As the sun rose over the Cappadocia region, it revealed other balloons floating in the sky and some chimney-like rock formations on the ground below — a transcendent experience that her 9-year-old likened to a dream. “That’s what we all felt because it was way too magical,” Ms. Lemay said.Six months ago, Ms. Lemay, 44, and her husband, Sebastien Pelletier, 45, left their home in the Montreal area for a yearlong trip across Asia and Africa. Three of the French Canadian couple’s four children have a rare eye condition that has already impaired their vision and will slowly destroy it entirely unless an effective treatment materializes. The trip is a chance for them to see memorable sites while they still can.Mia Pelletier, 11, on a hot-air balloon ride in central Turkey in July.Edith LemayIn another sense, Ms. Lemay said, her family’s journey across Asia and Africa is a catalyst for her three children with retinitis pigmentosa — Laurent, 5, Colin, 7, and Mia, 11 — to develop what she called “solution-oriented” behavior in the face of setbacks large and small, a habit that could prove useful as their eyesight continues to diminish. (Her oldest boy, Leo, 9, does not have the condition.)Ms. Lemay said she also hoped the trip would force her children to appreciate how lucky they are in a world where many of their peers do not have electricity in their homes, books in their schools or other comforts that people in wealthy countries take for granted.“I want them to look at their life and see what’s good, what’s beautiful in it,” she said by phone last month from Indonesia, as Laurent splashed in a nearby swimming pool. “Not the little problem with their eyes.”The prognosisRetinitis pigmentosa encompasses a group of hereditary disorders that affect an estimated one in 3,000 to 4,000 people worldwide, including as many as 110,000 in the United States, according to the National Organization for Rare Disorders, a nonprofit in Massachusetts. It causes slow degradation of the retina, and the symptoms can develop over decades.The family walking through a spice market in Zanzibar, off the coast of Tanzania, after an overland trip across southern Africa in the spring.Edith LemayPeople with retinitis pigmentosa typically begin to lose their vision during childhood. In the next phase of the disease’s progression, they start to lose their peripheral vision, making it hard for some children to play sports or to avoid bumping into their classmates in the hallways, said Alfred S. Lewin, a professor emeritus of molecular genetics and microbiology at the University of Florida in Gainesville.In advanced stages of the condition, their vision becomes so impaired that they are considered legally blind, though most do not completely lose their ability to detect light, Dr. Lewin said. But several promising new experimental therapies are in human clinical trials and could be approved in the next few years, potentially helping many children and young adults with the condition avoid blindness, he added.Playing soccer with local boys in Zanzibar.Edith LemayMeeting an eagle hunter near Ulan Bator, the capital of Mongolia.Edith LemayFor now, existing therapies can help slow the progression of the condition, said Lin Bin, a professor of optometry at Hong Kong Polytechnic University.“These treatments can buy time for the patients for new research breakthroughs and new and more effective treatments,” he said.Facing realityMs. Lemay said that while she and her husband were cautiously hoping for a breakthrough treatment, they did not want to set themselves or their children up for disappointment.“If a new treatment comes, good, we’ll be super happy,” she said in mid-September from the Gili Islands of Indonesia, where her children had just snorkeled with turtles. “But we’re not going to be sitting there waiting on a cure. We want our children to accept their situation and learn how to make the best of it.”Swimming in a cave in Zanzibar.Edith LemayAt this early stage, the children do not talk much about their eyesight, and they occasionally even crack jokes about their condition, Ms. Lemay said. The only reason she has been discussing it so much lately is because reporters keep calling to ask about the round-the-world trip.“It’s not something sad in our family,” she said. “It’s just something that’s going to happen, and we’re going to face it.”At the same time, she said, it can be hard to discuss retinitis pigmentosa with her children, especially Laurent, who doesn’t yet understand its full implications. “How am I going to cross the street?” he asked her this summer as the family drove through the Mongolian Steppes in a Russian-built van. “Will my wife be blind?”Looking at wildlife on a Serengeti safari in Tanzania.Edith LemayAnother time in Mongolia, Ms. Lemay was gazing at the Gobi Desert’s night sky when she remembered that her three children who have the condition cannot see stars because of their night-vision loss. She did not bother to wake them up.Seeing the sitesMs. Lemay said that the trip so far had been loaded with adventure and serendipity, and that her children never seemed to become bored.Their journey began with a three-month, coast-to-coast, overland trip across southern Africa. An early highlight for the children, she said, was a 24-hour train ride across Tanzania, where they slept in bunk beds and watched in awe as vendors approached the windows to hawk bananas.Mia, 11, looking at a rainbow from the roof of the family van in Mongolia.Edith LemayRiding an overnight train across Tanzania.Edith LemayAfter a month in Turkey, the family traveled to Mongolia and spent more than a month on a road trip through the countryside, staying in yurts and eating boiled mutton.The children loved that, too, even if the toilet facilities along the way ranged from “abominable to bearable,” as Ms. Lemay put it on her Facebook page. Her daughter, Mia, enjoyed riding horses so much that she cried tears of joy. And even though Mia and two of her brothers can no longer see stars, they enjoyed looking at pictures of the Gobi’s night sky on their mother’s laptop.Soyolsaikhan Baljinnyum, the family’s tour guide in Mongolia, said by phone that the family was one of the kindest he had ever met.“It really hurts me when I think about them losing their vision,” he said of the three children with the eye condition. “But there’s always hope; there could be a miracle.”Ms. Lemay, who works in health care logistics, said her family planned to spend the next two months island-hopping across Indonesia by boat and bus. From there, they intend to visit Malaysian Borneo, Thailand, Cambodia and Vietnam, with a potential stop in Hawaii on their way back to Canada. But it’s all subject to change: Their itinerary is fixed only about a month in advance.Sitting in an ancient theater near Pamukkale, Turkey, in July.Edith LemayAmong the surprises so far, Ms. Lemay said, is the way her children tend to fixate on things that seem peripheral to whatever their parents had planned to show them, such as stray cats and dogs, or a tiny beetle they spotted at the base of a colossal red sand dune in Namibia.“Hey, we came all the way around the world to see that, and you’re looking at a little bug?” Ms. Lemay said she asked them at the UNESCO World Heritage site.“But if we listen to them,” she added, “they show us that there is beauty everywhere.”

A group of biologists and other scientists said humans began growing cannabis about 12,000 years ago not just for food, but also for hemp and, yes, probably to get high.People feeling the effects of marijuana are prone to what scientists call “divergent thinking,” the process of searching for solutions to a loosely defined question.Here’s one to ponder: Where did the weed come from? No, not where it was bought, but where and when was the plant first domesticated?Many botanists believe that the cannabis sativa plant was first domesticated in Central Asia. But a new study published on Friday in the journal Science Advances suggests that East Asia is the more likely source, and that all existing strains of the plant come from an “ancestral gene pool” represented by wild and cultivated varieties growing in China today.The study’s authors found that the plant was a “primarily multipurpose crop” grown about 12,000 years ago during the early Neolithic period, probably for fiber and medicinal uses.Farmers began breeding the plant specifically for its mind-altering properties about 4,000 years ago, as cannabis began to spread into Europe and the Middle East, the authors of the study said.Michael Purugganan, a professor of biology at New York University who read the study, said the usual assumption about early humans was that they domesticated plants for food.“That seems to be the most pressing problem for humans then: How to get food,” said Professor Purugganan, who was not involved in the research. “The suggestion that even early on they were also very concerned with fiber and even intoxicants is interesting. It would bring to question what were the priorities of these Neolithic societies.”A 2016 study by other scientists said that the earliest records for cannabis were mostly from China and Japan, but most botanists believe that it was probably first domesticated in the eastern part of Central Asia, where wild varieties of the plant are widespread.Genetic sequencing for the latest study suggests that the species has a “single domestication origin” in East Asia, the researchers wrote.By sequencing genetic samples of the plant, they found that the species had most likely been domesticated by the early Neolithic period. They said their conclusion was supported by pottery and other archaeological evidence from the same period that was discovered in present-day China, Japan and Taiwan.But Professor Purugganan said he was skeptical about conclusions that the plant was developed for drug or fiber use 12,000 years ago since archaeological evidence show the consistent use or presence of cannabis for those purposes began about 7,500 years ago.“I would like to see a much larger study with a larger sampling,” he said.Luca Fumagalli, an author of the study and a biologist in Switzerland who specializes in conservation genetics, said the theory of a Central Asian origin was largely based on observational data of wild samples in that region.“It’s easy to find feral samples, but these are not wild types,” Dr. Fumagalli said. “These are plants that escaped captivity and readapted to the wild environment.”“By the way, that’s the reason you call it weed, because it grows anywhere,” he added.The study was led by Ren Guangpeng, a botanist at Lanzhou University in the western Chinese province of Gansu. Dr. Ren said in an interview that the original site of cannabis domestication was most likely northwestern China, and that the finding could help with current efforts in the country to breed new types of hemp.To conduct the study, Dr. Ren and his colleagues collected 82 samples, either seeds or leaves, from around the world. The samples included strains that had been selected for fiber production, and others from Europe and North America that were bred to produce high amounts of tetrahydrocannabinol (THC), the plant’s most mood-altering compound.Dr. Fumagalli and his colleagues then extracted genomic DNA from the samples and sequenced them in a lab in Switzerland. They also downloaded and reanalyzed sequencing data from 28 other samples. The results showed that the wild varieties they analyzed were in fact “historical escapes from domesticated forms,” and that existing strains in China — cultivated and wild — were their closest descendants of the ancestral gene pool.“Although additional sampling of feral plants in these key geographical areas is still needed, our results, which are based on very broad sampling already, would suggest that pure wild progenitors of C. sativa have gone extinct,” they wrote.As hemp’s function as a global source for textiles, food and oilseed dried up in the 20th century, the use of cannabis as a recreational drug increased, the new study noted. But there are still “large gaps” in knowledge about its domestication history, it said, in large part because the plant is illegal in many countries.It can also be hard to understand precisely how plant species are domesticated in the first place, said Catherine Rushworth, a postdoctoral researcher at the University of Minnesota who studies plant evolution.Although scientists can make some basic predictions about how a given plant species will diverge in nature, she added, such predictions “go out the window” when a natural selection process is driven by humans.“So, for example, we might think that species would diverge when they’re adapting to different habitats, or to different pollinators,” she said. “But people are often the pollinators and people have created those habitats.”Joy Dong

A group of biologists and other scientists said humans began growing cannabis about 12,000 years ago not just for food, but also for hemp and, yes, probably to get high.People feeling the effects of marijuana are prone to what scientists call “divergent thinking,” the process of searching for solutions to a loosely defined question.Here’s one to ponder: Where did the weed come from? No, not where it was bought, but where and when was the plant first domesticated?Many botanists believe that the cannabis sativa plant was first domesticated in Central Asia. But a new study published on Friday in the journal Science Advances suggests that East Asia is the more likely source, and that all existing strains of the plant come from an “ancestral gene pool” represented by wild and cultivated varieties growing in China today.The study’s authors found that the plant was a “primarily multipurpose crop” grown about 12,000 years ago during the early Neolithic period, probably for fiber and medicinal uses.Farmers began breeding the plant specifically for its mind-altering properties about 4,000 years ago, as cannabis began to spread into Europe and the Middle East, the authors of the study said.Michael Purugganan, a professor of biology at New York University who read the study, said the usual assumption about early humans was that they domesticated plants for food.“That seems to be the most pressing problem for humans then: How to get food,” said Professor Purugganan, who was not involved in the research. “The suggestion that even early on they were also very concerned with fiber and even intoxicants is interesting. It would bring to question what were the priorities of these Neolithic societies.”A 2016 study by other scientists said that the earliest records for cannabis were mostly from China and Japan, but most botanists believe that it was probably first domesticated in the eastern part of Central Asia, where wild varieties of the plant are widespread.Genetic sequencing for the latest study suggests that the species has a “single domestication origin” in East Asia, the researchers wrote.By sequencing genetic samples of the plant, they found that the species had most likely been domesticated by the early Neolithic period. They said their conclusion was supported by pottery and other archaeological evidence from the same period that was discovered in present-day China, Japan and Taiwan.But Professor Purugganan said he was skeptical about conclusions that the plant was developed for drug or fiber use 12,000 years ago since archaeological evidence show the consistent use or presence of cannabis for those purposes began about 7,500 years ago.“I would like to see a much larger study with a larger sampling,” he said.Luca Fumagalli, an author of the study and a biologist in Switzerland who specializes in conservation genetics, said the theory of a Central Asian origin was largely based on observational data of wild samples in that region.“It’s easy to find feral samples, but these are not wild types,” Dr. Fumagalli said. “These are plants that escaped captivity and readapted to the wild environment.”“By the way, that’s the reason you call it weed, because it grows anywhere,” he added.The study was led by Ren Guangpeng, a botanist at Lanzhou University in the western Chinese province of Gansu. Dr. Ren said in an interview that the original site of cannabis domestication was mostly likely northwestern China, and that the finding could help with current efforts in the country to breed new types of hemp.To conduct the study, Dr. Ren and his colleagues collected 82 samples, either seeds or leaves, from around the world. The samples included strains that had been selected for fiber production, and others from Europe and North America that were bred to produce high amounts of tetrahydrocannabinol (THC), the plant’s most mood-altering compound.Dr. Fumagalli and his colleagues then extracted genomic DNA from the samples and sequenced them in a lab in Switzerland. They also downloaded and reanalyzed sequencing data from 28 other samples. The results showed that the wild varieties they analyzed were in fact “historical escapes from domesticated forms,” and that existing strains in China — cultivated and wild — were their closest descendants of the ancestral gene pool.“Although additional sampling of feral plants in these key geographical areas is still needed, our results, which are based on very broad sampling already, would suggest that pure wild progenitors of C. sativa have gone extinct,” they wrote.As hemp’s function as a global source for textiles, food and oilseed dried up in the 20th century, the use of cannabis as a recreational drug increased, the new study noted. But there are still “large gaps” in knowledge about its domestication history, it said, in large part because the plant is illegal in many countries.It can also be hard to understand precisely how plant species are domesticated in the first place, said Catherine Rushworth, a postdoctoral researcher at the University of Minnesota who studies plant evolution.Although scientists can make some basic predictions about how a given plant species will diverge in nature, she added, such predictions “go out the window” when a natural selection process is driven by humans.“So, for example, we might think that species would diverge when they’re adapting to different habitats, or to different pollinators,” she said. “But people are often the pollinators and people have created those habitats.”Joy Dong

Some celebrity vaccine endorsements have delighted social media users. But epidemiologists say there isn’t much evidence proving that they boost vaccine uptake.Pelé, Dolly Parton and the Dalai Lama have little in common apart from this: Over a few days in March, they became the latest celebrity case studies for the health benefits of Covid-19 vaccines.“I just want to say to all of you cowards out there: Don’t be such a chicken squat,” Ms. Parton, 75, said in a video that she posted on Twitter after receiving her vaccine in Tennessee. “Get out there and get your shot.”This is hardly the first time public figures have thrown their popularity behind an effort to change the behavior of ordinary people. In medicine, celebrity endorsements tend to echo or reinforce messages that health authorities are trying to publicize, whether it’s getting a vaccine, or other medical treatment. In 18th-century Russia, Catherine the Great was inoculated against smallpox as part of her campaign to promote the nationwide rollout of the procedure. Almost 200 years later, backstage at “The Ed Sullivan Show,” Elvis Presley received the polio vaccine in an effort to help reach at-risk teenagers.But do the star-studded endorsements really work? Not necessarily. Epidemiologists say there are plenty of caveats and potential pitfalls — and little scientific evidence to prove that the endorsements actually boost vaccine uptake.“Very few people actually do give the weight of expertise, for better or worse, to celebrities,” said René F. Najera, an epidemiologist and the editor of the History of Vaccines website, a project of the College of Physicians of Philadelphia.Elvis Presley received the polio vaccine backstage at the “The Ed Sullivan Show” in 1956.CBS Photo Archive/Getty Images“There’s some shift there now with social media and social influence in the younger age groups,” he added. “But for the most part, we still listen more to our peers than to some figurehead.”As vaccination campaigns accelerate around the world, watching high-profile endorsements has become one of the latest — and among the weirdest — online rituals of the Covid era.To help track the phenomenon, New York Magazine over the winter kept a running list of newly vaccinated celebrities that includes Christie Brinkley (“piece of cake”), Whoopi Goldberg (“I didn’t feel it”) and Mandy Patinkin (“One of the few benefits of being old”). Journalists in India have done the same for Bollywood film stars.In Europe, pictures of male politicians getting their shots while shirtless have generated a bunch of memes. An epidemiologist in Oregon, Dr. Esther Choo, joked on Twitter that the French health minister, Olivier Véran, was carrying out a public-relations campaign that she called “Operation Smolder.”Such posts are notable because they instantly allow millions of people to see the raw mechanics of immunization — needles and all — at a time when skepticism toward Covid vaccines has been stubbornly persistent in the United States and beyond. The rapid-fire testimonials by Pelé, Ms. Parton and the Dalai Lama in March, for example, collectively reached more than 30 million followers and prompted hundreds of thousands of engagements across Twitter, Instagram and YouTube. In April, the singer Ciara hosted a star-studded NBC special meant to promote vaccinations, with appearances by former President Barack Obama and his wife, Michelle Obama, as well as Lin-Manuel Miranda, Jennifer Hudson, Matthew McConaughey and others.“These kind of endorsements might be especially important if trust in government/official sources is quite low,” Tracy Epton, a psychologist at the University of Manchester in Britain who has studied public health interventions during the coronavirus pandemic, said in an email.That was the case in the 1950s, when Elvis Presley agreed to receive the polio vaccine to help the National Foundation for Infantile Paralysis reach a demographic — teenagers — that was “difficult to educate and inspire through traditional means,” said Stephen E. Mawdsley, a lecturer in modern American history at the University of Bristol in Britain.“I think Elvis helped to make getting vaccinated seem ‘cool’ and not just the responsible thing to do,” Dr. Mawdsley said.There is some evidence that celebrity endorsements of a given medical behavior can have concrete results. After Katie Couric had a colonoscopy live on the “Today” show in 2000, for example, the number of colorectal screenings in the United States soared for about nine months.And in Indonesia, researchers found in a pre-coronavirus experiment that when 46 celebrities agreed to tweet or retweet pro-immunization messages, their posts were more popular than similar ones from noncelebrities. That was especially true when the celebrities delivered the message in their own voices, rather than citing someone else, researchers found. “Their voice matters,” said Vivi Alatas, an economist in Indonesia and a co-author of that study. “It’s not just their ability to reach followers.”For the most part, though, the science linking celebrity endorsements to behavioral change is tenuous.One reason is that people generally consider those within their own personal networks, not celebrities, the best sources of advice about changing their own behavior, Dr. Najera said.He cited a 2018 study that found few gun owners in the United States rated celebrities as effective communicators about safe gun storage. The owners were far more likely to trust law enforcement officers, active-duty military personnel, hunting or outdoor groups, and family members.From left, Arsenio Hall, Danny Trejo and Magic Johnson got their vaccines together in Los Angeles in March.Pool photo by Gina FerazziDr. Najera and other researchers have been convening focus groups of Americans to find out what has prompted them to agree — or not — to be vaccinated against Covid-19. He said the primary finding so far was that rates of uptake or hesitancy often corresponded to vaccine behavior among a given person’s racial, ethnic or socioeconomic peer group.Ho Phi Huynh, a professor of psychology at Texas A&M University-San Antonio, said that vaccine endorsements from celebrities tended to have a “spectrum of effect” because the degree of star admiration varies so much from fan to fan. Some see a celebrity merely as entertainment, Dr. Huynh said, while others form attachments to them that may compensate for a lack of authentic relationships in their own lives.“So going back to Dolly, if people perceive her to be a ‘typical liberal’ celebrity, there might be little influence for a large faction of the country,” he said.In Indonesia this winter, it took only a few hours for a mega-celebrity to undercut his own vaccine endorsement.The government had chosen the entertainer Raffi Ahmad, 34, to be among the first in the country to receive a Covid shot in January. “Don’t be afraid of vaccines,” he told his Instagram followers, who numbered nearly 50 million at the time, almost a fifth of the country’s population.That night, he was spotted partying without a mask, and accused of breaking the public’s trust.“Please you can do better than this,” Sinna Sherina Munaf, an Indonesian musician, told Mr. Ahmad and her nearly 11 million followers on Twitter. “Your followers are counting on you.”