Dr. Howard Bauchner will leave his post after a colleague suggested “taking racism out of the conversation” on a journal podcast.Following an outcry over comments about racism made by an editor at JAMA, the influential medical journal, the top editor, Dr. Howard Bauchner, will step down from his post effective June 30.The move was announced on Tuesday by the American Medical Association, which oversees the journal. Dr. Bauchner, who had led JAMA since 2011, had been on administrative leave since March because of an ongoing investigation into comments made on the journal’s podcast.Dr. Edward Livingston, another editor at JAMA, had claimed that socioeconomic factors, not structural racism, held back communities of color. A tweet promoting the podcast had said that no physician could be racist. It was later deleted.“I remain profoundly disappointed in myself for the lapses that led to the publishing of the tweet and podcast,” Dr. Bauchner said in a statement. “Although I did not write or even see the tweet, or create the podcast, as editor in chief, I am ultimately responsible for them.”Last month, the A.M.A.’s leaders admitted to serious missteps and proposed a three-year plan to “dismantle structural racism” within the organization and in medicine. The announcement on Tuesday did not mention the status of the investigation at JAMA. The journal declined further comment.“This is a real moment for JAMA and the A.M.A. to recreate themselves from a founding history that was based in segregation and racism to one that is now based on racial equity,” said Dr. Stella Safo, a Black primary care physician at the Icahn School of Medicine at Mount Sinai in New York.Dr. Safo and her colleagues started a petition, now signed by more than 9,000 people, that had called on JAMA to restructure its staff and hold a series of town hall conversations about racism in medicine. “I think that this is a step in the right direction,” she said of the announcement.But other critics said they were withholding judgment to see how the organization addressed what they saw as pervasive neglect of covering racism’s impact on health in its journals.“In the entire history of all the JAMA network journals, there’s only been one non-white editor,” noted Dr. Raymond Givens, a cardiologist at Columbia University in New York. In October, Dr. Givens wrote to Dr. Bauchner, noting that editors at the JAMA journals were overwhelmingly white and male. Dr. Bauchner did not respond, according to Dr. Givens.“This is not cause to celebrate,” he said of the announcement, adding that he had not intended to jeopardize Dr. Bauchner’s job. Nor will appointing a top editor of color resolve the issues, Dr. Givens said.“Looking for just a person of color misses the point,” he added. “I’m more interested in a bold voice. I want somebody who is willing to take a stand, push to move things forward.”The podcast that set the events in motion aired on Feb. 24 and did not include any Black researchers or experts on racism in medicine.“Structural racism is an unfortunate term,” Dr. Livingston, who is white, said on the podcast. “Personally, I think taking racism out of the conversation will help. Many people like myself are offended by the implication that we are somehow racist.”The podcast was promoted with a tweet from the journal that said, “No physician is racist, so how can there be structural racism in health care?” Following widespread protest in the medical community, the journal took down the podcast and deleted the tweet.“Comments made in the podcast were inaccurate, offensive, hurtful and inconsistent with the standards of JAMA,” Dr. Bauchner said in a statement released a week later. “We are instituting changes that will address and prevent such failures from happening again.”Dr. Livingston later resigned, and the A.M.A. placed Dr. Bauchner on administrative leave on March 25.The JAMA family of journals added four new titles under Dr. Bauchner’s leadership, and expanded to include podcasts, videos and new, shorter article types. But critics noted that the journals rarely addressed structural racism in medicine, and more often published papers linking health disparities to socioeconomic or biological factors.Dr. Bauchner’s exit offered the journals a chance to improve, said Dr. Mary Bassett, professor of the practice of health and human rights at Harvard University.“Medical journals have helped build the racist idea that races have intrinsic differences that have a bearing on health,” Dr. Bassett said. Journals are “challenged to embrace, not only accept, racism as a health issue.”Dr. Bauchner told The New York Times last month that JAMA had published “more than 100 articles on issues such as social determinants of health, health care disparities and structural racism over just the last five years.” He also noted that JAMA accepted only a tiny fraction of the manuscripts it had received.He said in the statement on Tuesday that the journal would be better served by his resignation. “The best path forward for the JAMA Network, and for me personally, is to create an opportunity for new leadership at JAMA,” he said.In an editorial published in JAMA on Tuesday, colleagues at the journal lauded Dr. Bauchner’s leadership, saying he “has left an indelible legacy of progress, innovation and excellence in medical journalism.”The A.M.A. said it has begun a search for Dr. Bauchner’s replacement. The journal’s executive editor, Dr. Phil Fontanarosa, will serve as interim editor in chief.Whoever the new editor may be, he or she will need to acknowledge the profound impact of structural racism on health outcomes for communities of color, Dr. Bassett said.“Racism works in ways that are structural and not simply as the result of ignorant, misguided or even racist individuals,” she added. “As a new editor in chief is sought, there will be a chance for JAMA to lead in dismantling this idea. I hope they grab it.”

The agency is reviewing several dozen reports that teenagers and young adults may have developed myocarditis after vaccination, officials said. But the agency has not determined whether the vaccine caused the condition.The Centers for Disease Control and Prevention is looking into reports that a very small number of teenagers and young adults vaccinated against the coronavirus may have experienced heart problems, according to the agency’s vaccine safety group.The group’s statement was sparse in details, saying only that there were “relatively few” cases and that they may be entirely unrelated to vaccination. The condition, called myocarditis, is an inflammation of the heart muscle, and can occur following certain infections.The C.D.C.’s review of the reports is in the early stages, and the agency has yet to determine whether there is any evidence that the vaccines caused the heart condition. It has posted some guidance on its website for doctors and clinicians to be alert to unusual heart symptoms among young people who had just received their shots.“It may simply be a coincidence that some people are developing myocarditis after vaccination,” said Dr. Celine Gounder, an infectious disease specialist at Bellevue Hospital Center in New York. “It’s more likely for something like that to happen by chance, because so many people are getting vaccinated right now.”The cases seem to have occurred predominantly in adolescents and young adults about four days after their second dose of one of the mRNA vaccines, which are Moderna and Pfizer-BioNTech. And the cases were more common in males than in females.“Most cases appear to be mild, and follow-up of cases is ongoing,” the vaccine safety group said. The C.D.C. strongly recommends Covid vaccines for Americans ages 12 and older.“We look forward to seeing more data about these cases, so we can better understand if they are related to the vaccine or if they are coincidental,” said Dr. Yvonne Maldonado, chair of the American Academy of Pediatrics’s Committee on Infectious Diseases. “Meanwhile, it’s important for pediatricians and other clinicians to report any health concerns that arise after vaccination.”Experts emphasized that the potentially rare side effect of myocarditis paled in comparison to the potential risks of Covid, including the persistent syndrome called “long Covid.” Acute Covid itself can cause myocarditis. As of May 13, the coronavirus has infected more than 3.9 million children and sent more than 16,000 to hospitals, more than are hospitalized for flu in an average year, according to data collected by the A.A.P. About 300 children have died of Covid-19 in the United States, making it one of the top 10 causes of death in children since the pandemic began.“And that’s in the context of all the mitigation measures taken,” said Dr. Jeremy Faust, an emergency medicine physician at Brigham and Women’s Hospital in Boston.In the general population, about 10 to 20 of every 100,000 people each year develop myocarditis, or an inflammation of the heart, experiencing symptoms ranging from fatigue and chest pain to arrhythmias and cardiac arrest. Many others likely have mild symptoms and are never diagnosed, according to researchers.At the moment, the number of cases of myocarditis reported after vaccination does not appear to be greater than would normally be seen in young people, according to the C.D.C. But members of the agency’s vaccine safety group “felt that information about reports of myocarditis should be communicated to providers,” the report said.The agency did not specify the ages of the patients involved. The Pfizer-BioNTech vaccine has been authorized for ages 16 and above since December. Earlier this month, the Food and Drug Administration extended that authorization to children 12 through 15 years of age.On May 14, the C.D.C. alerted clinicians to the possible link between myocarditis and vaccines. And on May 17, the working group reviewed data on myocarditis from the Department of Defense, reports filed with the Vaccine Adverse Event Reporting System and others.State health departments in Washington, Oregon and California have alerted emergency providers and cardiologists to the potential problem, and a report of seven cases has been submitted to the journal Pediatrics for review.Dr. Liam Yore, past president of the Washington State chapter of the American College of Emergency Physicians, said in an interview that he recently had seen a teenager with myocarditis after vaccination.The patient was treated for mild inflammation of the lining of the heart, and was sent home afterward. But the teenager later returned for care with a decrease in the heart’s output. Still, Dr. Yore said he had seen worse outcomes in youngsters with Covid, including in a 9-year-old who had arrived at the hospital following a cardiac arrest last winter.“The relative risk is a lot in favor of getting the vaccine, especially considering how many doses of the vaccine have been administered,” he said.More than 161 million people in the United States have received at least one dose of a coronavirus vaccine; about 4.5 million of them were between 12 and 18 years of age.

Two scientific findings altered the calculus: Vaccinated people don’t transmit the virus, and the shots are effective against variants.Advice from federal health officials that fully vaccinated people could drop their masks in most settings came as a surprise to Americans, from state officials to scientific experts. Even the White House got less than a day’s notice from the Centers for Disease Control and Prevention, the press secretary, Jen Psaki, said at a news briefing on Friday.“The C.D.C., the doctors and medical experts there, are the ones who determined what this guidance would be based on their own data, and what the timeline would be,” Ms. Psaki said. “That was not a decision directed by or made by the White House.”For months, federal officials have vigorously warned that wearing masks and social distancing were necessary to contain the pandemic. So what changed?Introducing the new recommendations on Thursday, Dr. Rochelle P. Walensky, the C.D.C. director, cited two recent scientific findings as significant factors: Few vaccinated people become infected with the virus, and transmission seems rarer still; and the vaccines appear to be effective against all known variants of the coronavirus.There is no doubt at this point that the vaccines are powerful. On Friday, the C.D.C. released results from another large study showing that the vaccines made by Pfizer-BioNTech and Moderna are 94 percent effective in preventing symptomatic illness in those who were fully vaccinated, and 82 percent effective even in those only partly vaccinated.“The science is quite clear on this,” said Zoë McLaren, a health policy expert at the University of Maryland, Baltimore County. Mounting evidence indicates that people who are vaccinated are highly unlikely to catch or transmit the virus, she noted.The risk “is definitely not zero, but it’s clear that it’s very low,” she said.One of the lingering concerns among scientists had been that even a vaccinated person might carry the virus — perhaps briefly, without symptoms — and spread it to others. But C.D.C. research, including the new study, has consistently found few infections among those who received the Pfizer-BioNTech and Moderna vaccines.“This study, added to the many studies that preceded it, was pivotal to C.D.C. changing its recommendations for those who are fully vaccinated against Covid-19,” Dr. Walensky said in a statement on Friday.Other recent studies confirm that people who are infected after vaccination carry too little virus to infect others, said Florian Krammer, a virologist at the Icahn School of Medicine at Mount Sinai.“It’s really hard to even sequence the virus sometimes because there’s very little virus, and it’s there for a short period of time,” he said.Still, most of the data has been gathered on the Pfizer-BioNTech and Moderna vaccines, Dr. Krammer cautioned. Because Johnson & Johnson’s vaccine was authorized later, there are fewer studies assessing its effectiveness.In clinical trials, the Johnson & Johnson vaccine had 72 percent efficacy — lower than the figure for the Pfizer and Moderna vaccines. And effectiveness was measured in terms of moderate and severe disease, rather than mild disease.“It’s a very good vaccine, and I’m sure it will save many, many, many lives,” Dr. Krammer said. “But we need more data on how well the J.&J. vaccine prevents infection, and how well it prevents transmission.”Variants of the virus have been a particular worry for scientists. While Dr. Walensky cited evidence showing that the mRNA vaccines like those from Pfizer and Moderna are effective against the variants circulating in the United States, there is little data about variants and the Johnson & Johnson vaccine. And new variants are emerging constantly.“I’m not at all saying that this is now a big problem,” Dr. Krammer said. But before lifting the masking requirements, “I might have waited a little bit longer to look at the numbers.”In a statement on Friday, a C.D.C. spokesman said, “All of the authorized vaccines provide strong protection against serious illness, hospitalization, and death, and we are accumulating data that our authorized vaccines are effective against the variants that are circulating in this country.”Fully immunized people are unlikely to get seriously ill, even if they are infected with the coronavirus. The risk of infection is greater for the people around them — unvaccinated children and adults, or vaccinated people who remain unprotected because of a medical condition or treatment.C.D.C. officials said they weighed those factors and were confident in their assessment of the science. And the new advice has other salutary effects, rewarding fully immunized people by giving them permission to end their social isolation — and perhaps incentivizing others to opt for vaccination.The new advice “signals that we really are on the final stretch here, and I think that’s a very good thing for people,” said Dr. Joshua Sharfstein, the vice dean for public health practice and community engagement at Johns Hopkins University Bloomberg School of Health.“It’s unlikely that we’re going to have another huge surge in cases,” he added. “But will the final stretch last for weeks or months is still a question.”The difficulty with the new recommendations, he and other experts said, is not so much the science underpinning them as their implementation.Leaders at the state, city and county levels still have the authority to require masks even for vaccinated people, as the C.D.C. was quick to acknowledge on Thursday. After the agency’s announcement, some states instantly lifted mask mandates, while others said they would need more time to weigh the evidence.But in states without mask mandates, the onus of checking vaccination status will fall on shopkeepers, restaurant workers, school officials and workplace managers.“Without a means to verify vaccination, we will have to rely on an honor system,” said Caitlin Rivers, an epidemiologist at Johns Hopkins University.The number of cases in the country is the lowest it has been since September, and many experts support lifting mask mandates in much of the country. But doing so will be riskier in places like Michigan, where there are more cases, and for people who are unprotected, including children under 12 and people with a weak immune systems, Dr. Rivers said.“People who are unvaccinated should continue to wear masks in public indoors and avoid crowds,” she said.In Nacogdoches, Texas, Dr. Ahammed Hashim fretted that only 36 percent of the population was immunized and the pace seemed to have stalled. And yet only one or two people in 10 in the local shops wore masks.“I think the C.D.C. might send a wrong message saying that everything’s OK,” said Dr. Hashim, a pulmonologist. “It would feel much better if we had a 60 or 70 percent vaccination.”The C.D.C.’s guidance is intended for fully vaccinated individuals, and should only be interpreted as such, Dr. Sharfstein cautioned. Nationwide, only 36 percent of the population is fully vaccinated.“What we’re just seeing is a little bit of the distance between advice that is entirely appropriate for people who are vaccinated, and the reality that there are places that still are seeing viral transmission and a lot of people who aren’t vaccinated,” he said.Individuals may make choices based on their perception of their own risks, but state and local leaders must decide what’s best for the community based on the rate of infections. “Those are two different things,” Dr. Sharfstein said. “And when they get conflated, that’s when people may make bad judgments about policy.”The new guidelines should serve as a reminder to health officials to step up their outreach and investment to ensure that everyone has access to vaccines, Dr. McLaren said. Parents of children under 12 should continue to urge them to wear masks indoors.The C.D.C.’s new policy shifts the onus onto the immunocompromised as well, to protect themselves from unmasked and unvaccinated people.“When we make policy, we need to balance the needs and desires of everyone,” Dr. McLaren said. “We could keep masking forever, but there are benefits to getting back to a life that looks more normal.”Health officials should emphasize that the situation may yet change, and official recommendations with it, she added: “We really need to practice being good at responding to changing situations.”

The researchers issued a call to action to improve indoor air quality as a safeguard against the spread of contagions like the coronavirus.Clean water in 1842, food safety in 1906, a ban on lead-based paint in 1971. These sweeping public health reforms transformed not just our environment but expectations for what governments can do.Now it’s time to do the same for indoor air quality, according to a group of 39 scientists. In a manifesto of sorts published on Thursday in the journal Science, the researchers called for a “paradigm shift” in how citizens and government officials think about the quality of the air we breathe indoors.The timing of the scientists’ call to action coincides with the nation’s large-scale reopening as coronavirus cases steeply decline: Americans are anxiously facing a return to offices, schools, restaurants and theaters — exactly the type of crowded indoor spaces in which the coronavirus is thought to thrive.There is little doubt now that the coronavirus can linger in the air indoors, floating far beyond the recommended six feet of distance, the experts declared. The accumulating research puts the onus on policymakers and building engineers to provide clean air in public buildings and to minimize the risk of respiratory infections, they said.“We expect to have clean water from the taps,” said Lidia Morawska, the group’s leader and an aerosol physicist at Queensland University of Technology in Australia. “We expect to have clean, safe food when we buy it in the supermarket. In the same way, we should expect clean air in our buildings and any shared spaces.”Meeting the group’s recommendations would require new workplace standards for air quality, but the scientists maintained that the remedies do not have to be onerous. Air quality in buildings can be improved with a few simple fixes, they said: adding filters to existing ventilation systems, using portable air cleaners and ultraviolet lights — or even just opening the windows where possible.Dr. Morawska led a group of 239 scientists who last year called on the World Health Organization to acknowledge that the coronavirus can spread in tiny droplets, or aerosols, that drift through the air. The W.H.O. had insisted that the virus spreads only in larger, heavier droplets and by touching contaminated surfaces, contradicting its own 2014 rule to assume all new viruses are airborne.The W.H.O. conceded on July 9 that transmission of the virus by aerosols could be responsible for “outbreaks of Covid-19 reported in some closed settings, such as restaurants, nightclubs, places of worship or places of work where people may be shouting, talking or singing,” but only at short range.“For the source room, clearly more ventilation is a good thing,” said one of the study’s authors. But that air goes somewhere. Maybe more ventilation is not always the solution.”L. Morawska et al., Science 2021, with permission of AAASThe pressure to act on preventing airborne spread has recently been escalating. In February, more than a dozen experts petitioned the Biden administration to update workplace standards for high-risk settings like meatpacking plants and prisons, where Covid outbreaks have been rampant.Last month, a separate group of scientists detailed 10 lines of evidence that support the importance of airborne transmission indoors.On April 30, the W.H.O. inched forward and allowed that in poorly ventilated spaces, aerosols “may remain suspended in the air or travel farther than 1 meter (long-range).” The Centers for Disease Control and Prevention, which had also been slow to update its guidelines, recognized last week that the virus can be inhaled indoors, even when a person is more than six feet away from an infected individual.“They have ended up in a much better, more scientifically defensible place,” said Linsey Marr, an expert in airborne viruses at Virginia Tech, and a signatory to the letter.“It would be helpful if they were to undertake a public service messaging campaign to publicize this change more broadly,” especially in parts of the world where the virus is surging, she said. For example, in some East Asian countries, stacked toilet systems could transport the virus between floors of a multistory building, she noted.More research is also needed on how the virus moves indoors. Researchers at the Department of Energy’s Pacific Northwest National Laboratory modeled the flow of aerosol-size particles after a person has had a five-minute coughing bout in one room of a three-room office with a central ventilation system. Clean outdoor air and air filters both cut down the flow of particles in that room, the scientists reported in April.But rapid air exchanges — more than 12 in an hour — can propel particles into connected rooms, much as secondhand smoke can waft into lower levels or nearby rooms.“For the source room, clearly more ventilation is a good thing,” said Leonard Pease, a chemical engineer and lead author of the study. “But that air goes somewhere. Maybe more ventilation is not always the solution.”In the United States, the C.D.C.’s concession may prompt the Occupational Safety and Health Association to change its regulations on air quality. Air is harder to contain and clean than food or water. But OSHA already mandates air-quality standards for certain chemicals. Its guidance for Covid does not require improvements to ventilation, except for health care settings.“Ventilation is really built into the approach that OSHA takes to all airborne hazards,” said Peg Seminario, who served as director of occupational safety and health for the A.F.L.-C.I.O. from 1990 until her retirement in 2019. “With Covid being recognized as an airborne hazard, those approaches should apply.”In January, President Biden directed OSHA to issue emergency temporary guidelines for Covid by March 15. But OSHA missed the deadline: Its draft is reportedly being reviewed by the White House’s regulatory office.Workers installed ventilation equipment at University Hospital in Augusta, Ga., last year. As a group of scientists called for new workplace air quality improvements, they contended the measures would not be onerous. Michael Holahan/The Augusta Chronicle, via Associated PressIn the meantime, businesses can do as much or as little as they wish to protect their workers. Citing concerns of continued shortages of protective gear, the American Hospital Association, an industry trade group, endorsed N95 respirators for health care workers only during medical procedures known to produce aerosols, or if they have close contact with an infected patient. Those are the same guidelines the W.H.O. and the C.D.C. offered early in the pandemic. Face masks and plexiglass barriers would protect the rest, the association said in March in a statement to the House Committee on Education and Labor.“They’re still stuck in the old paradigm, they have not accepted the fact that talking and coughing often generate more aerosols than do these so-called aerosol-generating procedures,” Dr. Marr said of the hospital group.“We know that Plexiglas barriers do not work,” she said, and may in fact increase the risk, perhaps because they inhibit proper airflow in a room.The improvements do not have to be expensive: In-room air filters are reasonably priced at less than 50 cents per square foot, although a shortage of supply has raised prices, said William Bahnfleth, professor of architectural engineering at Penn State University, and head of the Epidemic Task Force at Ashrae (the American Society of Heating, Refrigerating and Air-Conditioning Engineers), which sets standards for such devices. UV lights that are incorporated into a building’s ventilation system can cost up to roughly $1 per square foot; those installed room by room perform better but could be 10 times as expensive, he said.If OSHA rules do change, demand could inspire innovation and slash prices. There is precedent to believe that may happen, according to David Michaels, a professor at George Washington University who served as OSHA director under President Barack Obama.When OSHA moved to control exposure to a carcinogen called vinyl chloride, the building block of vinyl, the plastics industry warned it would threaten 2.1 million jobs. In fact, within months, companies “actually saved money and not a single job was lost,” Dr. Michaels recalled.In any case, absent employees and health care costs can prove to be more costly than updates to ventilation systems, the experts said. Better ventilation will help thwart not just the coronavirus, but other respiratory viruses that cause influenza and common colds, as well as pollutants.Before people realized the importance of clean water, cholera and other waterborne pathogens claimed millions of lives worldwide every year.“We live with colds and flus and just accept them as a way of life,” Dr. Marr said. “Maybe we don’t really have to.”

The shots may allow millions of youngsters to get back to school, camps, sleepovers and hangouts with friends.The Food and Drug Administration on Monday authorized use of the Pfizer-BioNTech Covid-19 vaccine for 12- to 15-year-olds in the United States, a crucial step in the nation’s steady recovery from the pandemic and a boon to millions of American families eager for a return to normalcy.The authorization caps weeks of anticipation among parents, who have been grappling with how to conduct their lives when only the adults in a household are immunized. It removes an obstacle to school reopenings by reducing the threat of transmission in classrooms, and affords more of the nearly 17 million children in this age group opportunities to attend summer camps, sleepovers and Little League games.“This is great news,” said Dr. Kristin Oliver, a pediatrician and vaccine expert at Mount Sinai Hospital in New York. “It feels like we’ve been waiting a long time to start protecting children in this age group.” The Pfizer-BioNTech vaccine is already available to anyone over 16.The F.D.A.’s go-ahead is not the final hurdle. An advisory committee of the Centers for Disease Control and Prevention is expected to meet shortly to review the data and make recommendations for the vaccine’s use in 12- to 15-year-olds.If the committee endorses the vaccine for that age group, as expected, immunizations in theory can begin immediately. Clinical trials have shown that these children may safely receive the dose already available for adults.President Biden has said that about 20,000 pharmacies are ready to administer the vaccine to adolescents, and health officials in some states are already drawing up immunization campaigns targeted to youngsters.In a clinical trial, Pfizer and BioNTech enrolled 2,260 participants ages 12 and 15 and gave them either two doses of the vaccine or a placebo three weeks apart. The researchers recorded 18 cases of symptomatic coronavirus infection in the placebo group, and none among the children who received the vaccine, indicating that it was highly effective at preventing symptomatic illness.The vaccine also appeared to be safe for these children, with side effects comparable to those seen in trial participants who are 16 to 25 years old. Fevers were slightly more common among inoculated 12- to 15-year-olds; about 20 percent of them had fevers, compared with 17 percent in the older age group.The trend toward more fevers at younger ages was consistent with observations in an earlier trial, said Dr. Bill Gruber, a senior vice president at Pfizer and a pediatrician.The trial results were a “trifecta” of good news, Dr. Gruber added: “We have safety, we got the immune response we wanted — it was actually better than what we saw in the 16- to 25-year-old population — and we had outright demonstration of efficacy.”The company is still gathering information on potential asymptomatic infections by continuing to test the trial participants for the coronavirus every two weeks and checking them for antibodies produced in response to a natural infection, according to Dr. Gruber.The authorization arrives at a opportune time. Roughly one-third of eighth graders, usually 13 and 14 years old, are still learning fully remotely, and widespread vaccination may help speed a return to classrooms.Coronavirus outbreaks have been a concern particularly for students participating in team sports, and immunizations should ease the concerns of many parents whose children have been unable to participate in football, basketball and other team sports involving close contact.In summer, families often catch up the vaccinations required for children to return to schools in the fall, and so pediatricians and family doctors may be best positioned to immunize young teenagers as they come in for annual physical examinations.The Pfizer-BioNTech vaccine can be stored for only five days in standard refrigerators, but the companies are planning to ship smaller packs for doctors’ offices. It is also developing a formulation that can be refrigerated for up to 10 weeks.The push to immunize children may run into the same problems with hesitancy that have plagued attempts to inoculate adults. In one recent poll, 30 percent of parents said they would have their children vaccinated right away, while 26 percent said they planned to wait to see how the vaccine was working.Most of the other parents said they would definitely not have their children vaccinated, or would do so only if schools required it. All 50 states require certain vaccines for children who attend school, but those mandates apply only to vaccines that have been fully approved by the F.D.A. The Pfizer-BioNTech vaccine has been authorized only for emergency use.The companies have applied to the F.D.A. for full approval, but that process is expected to take several months. Even after approval, students may still opt out by citing medical reasons or religious beliefs.Still, scientists agreed that the vaccine appeared to meet all expectations regarding safety and efficacy. Dr. Megan Ranney, an emergency room physician and professor at Brown University in Providence, R.I., said she had “zero safety concerns” about the Pfizer-BioNTech vaccine, noting that hundreds of millions of people worldwide had received it.Her 12-year-old daughter is eager to be vaccinated, and her 9-year-old son will be immunized as soon as he is eligible, she said. Dr. Ranney has not allowed her children to sleep at friends’ houses since the pandemic began. The vaccine should allow them to safely resume social activities, she said.“The risk of your child catching Covid and getting really sick is low, but it’s not zero,” she said. “And the risk of them getting sick or hospitalized or worse with Covid or with the post-Covid multi-inflammatory syndrome is higher than the risk of something bad from this vaccine.”Vaccinating children shields others in the community from the virus, she noted, including people who are not protected by the vaccine, such as organ transplant recipients, cancer patients and those with impaired immune responses.“It also protects all of us from the virus continuing to spread and mutating further,” Dr. Ranney said. “That’s the thing that I’m most scared of right now.”Vaccinating children is crucial to building up population levels of immunity and curtailing the spread of the coronavirus. Though children spread the virus less efficiently than adults do, they make up about 23 percent of the population.Experts have said that the country is unlikely to reach the “herd immunity” threshold — the point at which virus transmission essentially stalls — but vaccinating children will be important for getting as close as possible.Ty Dropic, 14, one of the trial participants, urged others his age to be vaccinated so they could build up widespread immunity and protect themselves. He had no side effects, leading him to suspect that he got the placebo. If that turns out to be the case, he plans to be immunized as soon as possible.“I know it can be kind of scary, but it’s really not as bad as it seems,” he said. “If you do get Covid, it’ll be a lot worse than getting stuck with a needle for, like, two seconds.”Ty’s three siblings, ages 8, 10 and 16, are also enrolled in vaccine trials for their age groups. Their mother, Dr. Amanda Dropic, a pediatrician in northern Kentucky, said that in her practice, most parents were eager to have their children vaccinated so they could regain some semblance of normalcy.“The anxiety and depression that we’re seeing with kids, the social delays, has been tremendous,” she said.Dr. Dropic said her children understood the risks and were willing to volunteer because they saw it as a civic duty. Every medicine available today came to be because “somebody was willing to go first,” she added.Pfizer and BioNTech began testing the vaccine in children ages 5 to 11 in March, and last month extended the trial to even younger children, ages 2 to 5. The companies next plan to test children who are 6 months to 2 years old.Assuming trial results are encouraging, the companies expect to apply to the F.D.A. in September for emergency authorization to administer the vaccine to children ages 2 to 11.Results from trials of Moderna’s vaccine in 12- to 17-year-olds are expected in the next few weeks. Findings from another trial of the company’s vaccine in children 6 months to 12 years old should be available in the second half of this year.AstraZeneca is testing its vaccine in children 6 months and older. Johnson & Johnson plans to wait for results from trials in participants older than 12 before testing its vaccine in younger children.Jan Hoffman contributed reporting.

The Food and Drug Administration on Monday authorized use of the Pfizer-BioNTech Covid-19 vaccine for 12- to 15-year-olds in the United States, a crucial step in the nation’s steady recovery from the pandemic and a boon to tens of millions of American families eager for a return to normalcy.The authorization caps weeks of anticipation among parents, who have been grappling with how to conduct their lives when only the adults in a household are immunized. It removes an obstacle to school reopenings by reducing the threat of transmission in classrooms, and affords millions of adolescents the opportunity to attend summer camps, sleepovers and get-togethers with friends.“This is great news,” said Dr. Kristin Oliver, a pediatrician and vaccine expert at Mount Sinai Hospital in New York. “It feels like we’ve been waiting a long time to start protecting children in this age group.” The Pfizer-BioNTech vaccine is already available to anyone over 16.The F.D.A.’s go-ahead is not the final hurdle. An advisory committee of the Centers for Disease Control and Prevention is expected to meet shortly to review the data and make recommendations for the vaccine’s use in 12- to 15-year-olds.If the committee endorses the vaccine for that age group, as expected, immunizations in theory could begin immediately. Clinical trials have shown that these children may safely receive the dose already available for adults.In a clinical trial, Pfizer and BioNTech enrolled 2,260 participants ages 12 and 15 and gave them either two doses of the vaccine or a placebo three weeks apart. The researchers recorded 18 cases of symptomatic coronavirus infection in the placebo group, and none among the children who received the vaccine, indicating that it was highly effective at preventing symptomatic illness.The vaccine also appeared to be safe for these children, with side effects comparable to those seen in trial participants who are 16 to 25 years old. Fevers were slightly more common among inoculated 12- to 15-year-olds; about 20 percent of them had fevers, compared with 17 percent in the older age group.The trend toward more fevers at younger ages was consistent with observations in an earlier trial, said Dr. Bill Gruber, a senior vice president at Pfizer and a pediatrician.The trial results were a “trifecta” of good news, Dr. Gruber added: “We have safety, we got the immune response we wanted — it was actually better than what we saw in the 16- to 25-year-old population — and we had outright demonstration of efficacy.”The company is still gathering information on potential asymptomatic infections by continuing to test the trial participants for the coronavirus every two weeks and checking them for antibodies produced in response to a natural infection, according to Dr. Gruber.The push to immunize children may run into the same problems with hesitancy that have plagued attempts to inoculate adults. In one recent poll, just over half of parents said they were likely to have their children get a vaccine as soon as one was authorized.Dr. Megan Ranney, an emergency room physician at Rhode Island Hospital in Providence, said she had “zero safety concerns” about the Pfizer-BioNTech vaccine, noting that hundreds of millions of people worldwide have received it.Her 12-year-old daughter is eager to be vaccinated, and her 9-year-old son will be immunized as soon as he is eligible, she said.“The risk of your child catching Covid and getting really sick is low, but it’s not zero,” she said. “And the risk of them getting sick or hospitalized or worse with Covid or with the post-Covid multi-inflammatory syndrome is higher than the risk of something bad from this vaccine.”Vaccinating children shields others in the community from the virus, she noted, including people who are not protected by the vaccine, such as organ transplant recipients, cancer patients and those with impaired immune responses.“It also protects all of us from the virus continuing to spread and mutating further,” Dr. Ranney said. “That’s the thing that I’m most scared of right now.”Pfizer and BioNTech began testing the vaccine in children ages 5 to 11 in March and extended the trial to even younger children, ages 2 to 5, last month. The companies next plan to test children who are 6 months to 2 years old.Assuming trial results are encouraging, the companies expect to apply to the F.D.A. in September for emergency authorization to administer the vaccine to children ages 2 to 11.Results from trials of Moderna’s vaccine in 12- to 17-year-olds are expected in the next few weeks. Findings from another trial of the company’s vaccine in children 6 months to 12 years old should be available in the second half of this year.AstraZeneca is testing its vaccine in children 6 months and older. Johnson & Johnson plans to wait for results from trials in participants older than 12 before testing its vaccine in younger children.Jan Hoffman contributed reporting.

Widely circulating coronavirus variants and persistent hesitancy about vaccines will keep the goal out of reach. The virus is here to stay, but vaccinating the most vulnerable may be enough to restore normalcy.Early in the pandemic, when vaccines for the coronavirus were still just a glimmer on the horizon, the term “herd immunity” came to signify the endgame: the point when enough Americans would be protected from the virus so we could be rid of the pathogen and reclaim our lives.Now, more than half of adults in the United States have been inoculated with at least one dose of a vaccine. But daily vaccination rates are slipping, and there is widespread consensus among scientists and public health experts that the herd immunity threshold is not attainable — at least not in the foreseeable future, and perhaps not ever.Instead, they are coming to the conclusion that rather than making a long-promised exit, the virus will most likely become a manageable threat that will continue to circulate in the United States for years to come, still causing hospitalizations and deaths but in much smaller numbers.How much smaller is uncertain and depends in part on how much of the nation, and the world, becomes vaccinated and how the coronavirus evolves. It is already clear, however, that the virus is changing too quickly, new variants are spreading too easily and vaccination is proceeding too slowly for herd immunity to be within reach anytime soon.Continued immunizations, especially for people at highest risk because of age, exposure or health status, will be crucial to limiting the severity of outbreaks, if not their frequency, experts believe.“The virus is unlikely to go away,” said Rustom Antia, an evolutionary biologist at Emory University in Atlanta. “But we want to do all we can to check that it’s likely to become a mild infection.”The shift in outlook presents a new challenge for public health authorities. The drive for herd immunity — by the summer, some experts once thought possible — captured the imagination of large segments of the public. To say the goal will not be attained adds another “why bother” to the list of reasons that vaccine skeptics use to avoid being inoculated.Yet vaccinations remain the key to transforming the virus into a controllable threat, experts said.Dr. Anthony S. Fauci, the Biden administration’s top adviser on Covid-19, acknowledged the shift in experts’ thinking.“People were getting confused and thinking you’re never going to get the infections down until you reach this mystical level of herd immunity, whatever that number is,” he said.“That’s why we stopped using herd immunity in the classic sense,” he added. “I’m saying: Forget that for a second. You vaccinate enough people, the infections are going to go down.”Why reaching the threshold is toughCrowds on the National Mall in April. Resistance to the vaccines is a main reason the United States is unlikely to reach herd immunity, but it is not the only one.Amr Alfiky/The New York TimesOnce the novel coronavirus began to spread across the globe in early 2020, it became increasingly clear that the only way out of the pandemic would be for so many people to gain immunity — whether through natural infection or vaccination — that the virus would run out of people to infect. The concept of reaching herd immunity became the implicit goal in many countries, including the United States.Early on, the target herd immunity threshold was estimated to be about 60 to 70 percent of the population. Most experts, including Dr. Fauci, expected that the United States would be able to reach it once vaccines were available.But as vaccines were developed and distribution ramped up through the winter and into the spring, estimates of the threshold began to rise. That is because the initial calculations were based on the contagiousness of the original version of the virus. The predominant variant now circulating in the United States, called B.1.1.7 and first identified in Britain, is about 60 percent more transmissible.As a result, experts now calculate the herd immunity threshold to be at least 80 percent. If even more contagious variants develop, or if scientists find that immunized people can still transmit the virus, the calculation will have to be revised upward again.Polls show that about 30 percent of the U.S. population is still reluctant to be vaccinated. That number is expected to improve but probably not enough. “It is theoretically possible that we could get to about 90 percent vaccination coverage, but not super likely, I would say,” said Marc Lipsitch, an epidemiologist at the Harvard T.H. Chan School of Public Health.Though resistance to the vaccines is a main reason the United States is unlikely to reach herd immunity, it is not the only one.Herd immunity is often described as a national target. But that is a hazy concept in a country this large.“Disease transmission is local,” Dr. Lipsitch noted.“If the coverage is 95 percent in the United States as a whole, but 70 percent in some small town, the virus doesn’t care,” he explained. “It will make its way around the small town.”Uneven Willingness to Get Vaccinated Could Affect Herd ImmunityIn some parts of the United States, inoculation rates may not reach the threshold needed to prevent the coronavirus from spreading easily.

Even before the pandemic, many female scientists felt unsupported in their fields. Now, some are hitting a breaking point.Like many women during the pandemic, Alisa Stephens found working from home to be a series of wearying challenges.Dr. Stephens is a biostatistician at the University of Pennsylvania, and the technical and detail-oriented nature of her work requires long uninterrupted stretches of thought. Finding the time and mental space for that work with two young children at home proved to be an impossibility.“That first month was really hard,” she recalled of the lockdown. Her infant daughter’s day care was closed, and her 5-year-old was at home instead of at school. With their nanny unable to come to the house, Dr. Stephens tended to her children all day and worked late into the evening. In the fall, when her daughter was set to begin kindergarten, the schools did not reopen.Things eased once the family could safely bring in a nanny, but there was still little time for the deep thought Dr. Stephens had relied on each morning for her work. Over time, she has adjusted her expectations of herself.“Maybe I’m at 80 percent as opposed to 100 percent, but I can get things done at 80 percent to some extent,” she said. “It’s not great, it’s not my best, but it’s enough for now.”Dr. Stephens is in good company. Several studies have found that women have published fewer papers, led fewer clinical trials and received less recognition for their expertise during the pandemic.Add to that the emotional upheaval and stress of the pandemic, the protests over structural racism, worry about children’s mental health and education, and the lack of time to think or work, and an already unsustainable situation becomes unbearable.“The confluence of all of these factors creates this perfect storm. People are at their breaking point,” said Michelle Cardel, an obesity researcher at the University of Florida. “My big fear is that we are going to have a secondary epidemic of loss, particularly of early career women in STEM.”Female scientists were struggling even before the pandemic. It was not unusual for them to hear that women were not as smart as men, or that a woman who was successful must have received a handout along the way, said Daniela Witten, a biostatistician at the University of Washington in Seattle. Some things are changing, she said, but only with great effort, and at a glacial pace.The career ladder is particularly steep for mothers. Even during maternity leave, they are expected to keep up with lab work, teaching requirements, publications and mentoring of graduate students. When they return to work, most do not have affordable child care.Women in academia often have little recourse when confronted with discrimination. Their institutions sometimes lack the human resources structures common in the business world.Leslie Vosshall, a neuroscientist at Rockefeller University. “The older I get, the more of a window I have onto how this profession really works,” she said.Sarah Blesener for The New York TimesThe path is even rockier for scientists of color, like Dr. Stephens, who encounter other biases in the workplace — in everyday reactions, professional reviews or promotions — and now have to cope with the disproportionate impact of the pandemic on Black and Latino communities.Dr. Stephens said a close friend, also a Black scientist, had five family members who contracted Covid-19.The year has been a “pause” for everyone, Dr. Stephens added, and universities should find a way to help scientists when the pandemic ends — perhaps by adding an extra year to the time allotted to them to earn tenure.Others said while extra time for tenure may help, it will be far from enough.“It’s sort of like if you’re drowning, and the university tells you, ‘Don’t worry if it takes you an extra year to get back to shore,’” Dr. Witten said. “It’s like, ‘Hey, that’s not helpful. I need a flotation device.’”Compounding the frustration are the outdated notions about how to help women in science. But social media has allowed women to share some of those concerns and find allies to organize and call out injustice when they see it, said Jessica Hamerman, an immunologist at the Benaroya Research Institute in Seattle. “People are just much less likely to sit quietly, and listen to biased statements that affect them.”In November, for example, a controversial study on female scientists was published in the influential journal Nature Communications, suggesting that having female mentors would hinder the career of young scientists and recommending that the young women instead seek out men to help them.The response was intense and unforgiving.Hundreds of scientists, male and female, renounced the paper’s flawed methods and conclusions, saying it reinforced outdated stereotypes and neglected to take structural biases in academia into account.“The advice from the paper was basically similar to advice your grandmother may have given you 50 years ago: Get yourself a man who will take care of you, and all will be fine,” Dr. Cardel said.Nearly 7,600 scientists signed a petition calling on the journal to retract the paper — which it did on Dec. 21..css-1xzcza9{list-style-type:disc;padding-inline-start:1em;}.css-rqynmc{font-family:nyt-franklin,helvetica,arial,sans-serif;font-size:0.9375rem;line-height:1.25rem;color:#333;margin-bottom:0.78125rem;}@media (min-width:740px){.css-rqynmc{font-size:1.0625rem;line-height:1.5rem;margin-bottom:0.9375rem;}}.css-rqynmc strong{font-weight:600;}.css-rqynmc em{font-style:italic;}.css-akgeos{margin-bottom:15px;font-family:nyt-franklin,helvetica,arial,sans-serif;font-size:0.75rem;line-height:1rem;color:#787878;}@media (min-width:740px){.css-akgeos{font-size:0.8125rem;line-height:1.125rem;}}.css-yoay6m{margin:0 auto 5px;font-family:nyt-franklin,helvetica,arial,sans-serif;font-weight:700;font-size:1.125rem;line-height:1.3125rem;color:#121212;}@media (min-width:740px){.css-yoay6m{font-size:1.25rem;line-height:1.4375rem;}}.css-1dg6kl4{margin-top:5px;margin-bottom:15px;}#masthead-bar-one{display:none;}#masthead-bar-one{display:none;}.css-1pd7fgo{background-color:white;border:1px solid #e2e2e2;width:calc(100% – 40px);max-width:600px;margin:1.5rem auto 1.9rem;padding:15px;box-sizing:border-box;}@media (min-width:740px){.css-1pd7fgo{padding:20px;width:100%;}}.css-1pd7fgo:focus{outline:1px solid #e2e2e2;}#NYT_BELOW_MAIN_CONTENT_REGION .css-1pd7fgo{border:none;padding:20px 0 0;border-top:1px solid #121212;}.css-1pd7fgo[data-truncated] .css-rdoyk0{-webkit-transform:rotate(0deg);-ms-transform:rotate(0deg);transform:rotate(0deg);}.css-1pd7fgo[data-truncated] .css-eb027h{max-height:300px;overflow:hidden;-webkit-transition:none;transition:none;}.css-1pd7fgo[data-truncated] .css-5gimkt:after{content:’See more’;}.css-1pd7fgo[data-truncated] .css-6mllg9{opacity:1;}.css-1rh1sk1{margin:0 auto;overflow:hidden;}.css-1rh1sk1 strong{font-weight:700;}.css-1rh1sk1 em{font-style:italic;}.css-1rh1sk1 a{color:#326891;-webkit-text-decoration:underline;text-decoration:underline;text-underline-offset:1px;-webkit-text-decoration-thickness:1px;text-decoration-thickness:1px;-webkit-text-decoration-color:#ccd9e3;text-decoration-color:#ccd9e3;}.css-1rh1sk1 a:visited{color:#333;-webkit-text-decoration-color:#ccc;text-decoration-color:#ccc;}.css-1rh1sk1 a:hover{-webkit-text-decoration:none;text-decoration:none;}The study arrived at a time when many female scientists were already worried about the pandemic’s effect on their careers, and already on edge and angry with a system that offered them little support.“It’s been an incredibly difficult time to be a woman in science,” said Leslie Vosshall, a neuroscientist at Rockefeller University in New York. “We’re already on the ground, we’re already on our knees — and then the paper just comes and kicks us to say: ‘We have the solution, let’s move the graduate students to a senior man.’”Some people on Twitter suggested that the Nature Communications paper had been retracted because a “feminist mob” had demanded it, but in fact the paper was “a dumpster fire of data,” Dr. Vosshall said.The study was based on flawed assumptions and statistical analysis, according to several statisticians. (The authors of the paper declined to comment.)Dr. Vosshall said she felt compelled to push back because the paper was “dangerous.” Department chairs and deans of medical schools would have used the research to steer graduate students toward male mentors and roll back any progress toward making science more equitable, she said: “The older I get, the more of a window I have onto how this profession really works.”She has applied some of her wisdom to invoke change at Rockefeller University, one of the oldest research institutions in the country.A couple of years ago, Rockefeller University invited the news anchor Rachel Maddow to present a prestigious prize. On her way into the auditorium, Ms. Maddow pointed to a wall adorned with pictures of Lasker Award and Nobel Prize winners — all male — affiliated with the university. At least four women at the university had also won prestigious prizes, but their photographs were not on display.“What’s up with the dude wall?” Ms. Maddow asked. And Dr. Vosshall, who had walked past the wall a thousand times, suddenly saw it differently. She realized it sent the wrong message, overtly or not, to all the high school, undergraduate and graduate students who routinely walked past it.“Once you notice a dude wall, you see them everywhere,” she said. “They’re in every auditorium, every hallway, every departmental office, every conference room.”Rockefeller University eventually agreed to replace the display with one that is more representative of the institution’s history. The pictures were taken down on Nov. 11, Dr. Vosshall announced on Twitter, and will be replaced by a more inclusive set.Departments at Yale University and Brigham and Women’s Hospital in Boston have also reconsidered their dude walls, Dr. Vosshall said. “There are some traditions that should not be perpetuated.”

Researchers pushed back after the C.D.C. director asserted that vaccinated people “do not carry the virus.”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.The data suggest that “it’s much harder for vaccinated people to get infected, but don’t think for one second that they cannot get infected,” said Paul Duprex, director of the Center for Vaccine Research at the University of Pittsburgh.In a television interview with 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.”

Infected rodents pose no immediate danger to humans, but the research suggests that mutations are helping the coronavirus expand its range of potential hosts.Bats, humans, monkeys, minks, big cats and big apes — the coronavirus can make a home in many different animals. But now the list of potential hosts has expanded to include mice, according to an unnerving new study.Infected rodents pose no immediate risk to people, even in cities like London and New York, where they are ubiquitous and unwelcome occupants of subway stations, basements and backyards.Still, the finding is worrying. Along with previous work, it suggests that new mutations are giving the virus the ability to replicate in a wider array of animal species, experts said.“The virus is changing, and unfortunately it’s changing pretty fast,” said Timothy Sheahan, a virologist at the University of North Carolina at Chapel Hill, who was not involved in the new study.In the study, the researchers introduced the virus into the nasal passages of laboratory mice. The form of the virus first identified in Wuhan, China, cannot infect laboratory mice, nor can B.1.1.7, a variant that has been spreading across much of Europe, the researchers found.But B.1.351 and P1, the variants discovered in South Africa and Brazil, can replicate in rodents, said Dr. Xavier Montagutelli, a veterinarian and mouse geneticist at the Pasteur Institute in Paris, who led the study. The research, posted online earlier this month, has not yet been reviewed for publication in a scientific journal.The results indicate only that infection in mice is possible, Dr. Montagutelli said. Mice caught in the wild have not been found to be infected with the coronavirus, and so far, the virus does not seem to be able to jump from humans to mice, from mice to humans, or from mice to mice.“What our results emphasize is that it is necessary to regularly assess the range of species that the virus can infect, especially with the emergence of new variants,” Dr. Montagutelli said.The coronavirus is thought to have emerged from bats, with perhaps another animal acting as an intermediate host, and scientists worry that the virus may return to what they describe as an animal “reservoir.”Apart from potentially devastating those animal populations, a coronavirus spreading in another species may then acquire dangerous mutations, returning to humans in a form the current vaccines weren’t designed to fend off.A mink looks out from its cage at a farm in Denmark, where mink populations were hit hard by the coronavirus.Mads Claus Rasmussen/Agence France-Presse — Getty ImagesMinks are the only animals known to be able to catch the coronavirus from humans and pass it back. In early November, Denmark culled 17 million farmed mink to prevent the virus from evolving into dangerous new variants in the animals.More recently, researchers found that B.1.1.7 infections in domesticated cats and dogs can cause the pets to develop heart problems similar to those seen in people with Covid-19.To establish a successful infection, the coronavirus must bind to a protein on the surface of animal cells, gain entry into the cells, and exploit their machinery to make copies of itself. The virus must also evade the immune system’s early attempts at thwarting the infection.Given all those requirements, it is “quite extraordinary” that the coronavirus can infect so many species, said Vincent Munster, a virologist at the National Institute of Allergy and Infectious Diseases. “Typically, viruses have a more curtailed host range.”Mice are a known reservoir for hantavirus, which causes a rare and deadly disease in people. Even though the coronavirus variants don’t seem to be able to jump from mice to people, there is potential for them to spread among rodents, evolve into new variants, and then infect people again, Dr. Munster said.The variants may also threaten endangered species like black-footed ferrets. “This virus seems to be able to surprise us more than anything else, or any other previous virus,” Dr. Munster said. “We have to err on the side of caution.”Dr. Sheahan said he was more concerned about transmission to people from farm animals and pets than from mice.“You’re not catching wild mice in your house and snuggling — getting all up in their face and sharing the same airspace, like maybe with your cat or your dog,” he said. “I’d be more worried about wild or domestic animals with which we have a more intimate relationship.”But he and other experts said the results emphasized the need to closely monitor the rapid changes in the virus.“It’s like a moving target — it’s crazy,” he added. “There’s nothing we can do about it, other than try and get people vaccinated really fast.”