Though the number of epidemiologists in state health departments surged during the pandemic, the Centers for Disease Control and Prevention reported on Thursday that states were still far short of the public health workforces that officials said they needed.The report, based on a survey from early 2021 of state epidemiologists from all 50 states and the District of Columbia, reinforced broader concerns that public health workers across the country are less equipped to respond to a pandemic now than they were at the beginning of 2020.Even as the number of state epidemiologists grew, especially in fields like the Covid-19 response, staffing in general infectious diseases, chronic diseases, and maternal and child health declined, the C.D.C. said. Epidemiologists are responsible for tracking disease, developing responses, investigating health threats and studying public health services and health care.And although the number of state epidemiologists grew by 23 percent from 2017 to 2021, to a total of 4,136 positions, fewer states said in 2021 that they had the resources to fully monitor population health issues and to investigate and diagnose hazards that could affect people.In all, state officials said they needed another 2,196 epidemiologists to provide basic public health services, the survey found.“The Covid-19 response has strained the U.S. public health system,” the C.D.C. report said. “Workforce and capacity needs remain unmet.”The federal government has poured money into public health response activities during the pandemic, including $7.66 billion from the American Rescue Plan Act in 2021, the C.D.C. said. It is not clear how states’ public health needs or staffing levels had changed since the survey was conducted in 2021.The C.D.C. warned that public health needed predictable levels of funding over longer periods.Public health was often underfunded and neglected even before the pandemic. A combination of unpredictable funding, reduced authority to impose health orders and staffing problems have made the work of state and local public health departments all the more difficult.Funding for epidemiology was fragile, the C.D.C. reported. In 2021, epidemiology activities relied on federal money for 85 percent of their budgets, but states were unsure how long that money would last: 39 percent of the federal money was designated for Covid-19 work over limited time periods.The C.D.C. report tracked epidemiology positions only in state health departments, and not in other state agencies.Among the fields in which states reported being the shortest-staffed were genomics, mental health, oral health and occupational health.

Childhood environments shape people’s navigational skills, researchers reported. The findings one day may lead to better tests for early dementia.As a child in Chicago, Stephanie de Silva found that the city helped her get where she was going. Streets had directional names like “West” or “North,” and they often met at neat right angles. If all else failed, Lake Michigan could situate her.But when Ms. de Silva, 23, moved to London, where she now studies cognitive science, she suddenly could not navigate to a restaurant two blocks from home without a smartphone map. The streets were often crooked. Sometimes they seemed to lead nowhere.“I don’t think the cardinal directions exist here,” she said. “I’ve lived here for six months now, and I don’t know which direction I’m facing.”Scientists in Ms. de Silva’s lab at University College London, along with colleagues in Britain and France, have now arrived at an explanation: People who grow up in predictable, gridlike cities like Chicago or New York seem to struggle to navigate as easily as those who come from more rural areas or more intricate cities.Those findings, published in Nature on Wednesday, suggest that people’s childhood surroundings influence not only their health and well-being but also their ability to get around later in life. Much like language, navigation is a skill that appears to be most malleable when people’s brains are developing, the researchers concluded.The authors hope the findings eventually lead to navigation-based tests to help diagnose Alzheimer’s disease. Getting lost can sometimes occur earlier in the course of the illness than memory problems, they said.Researchers have developed virtual navigation tests for cognitive decline, but they can interpret the results only if they know what other factors influence people’s way-finding abilities.Among the forces shaping people’s navigation skills, the study suggested, was what kind of places they experienced as a child.“The environment matters,” said Hugo Spiers, a professor of cognitive neuroscience at University College London and one of the study’s lead authors. “The environment we’re exposed to has a knock-on effect, into the 70s, on cognition.”People in countries whose biggest cities were complex patchworks, like Barcelona, Spain, may have sharpened their navigational skills by dealing with chaotic street layouts, scientists suggested. Emilio Morenatti/Associated PressIt took a series of unlikely events — involving a cellphone company, a controversial YouTuber and a custom-made video game — to generate the large data set behind the study.In 2015, Michael Hornberger, who studies dementia at University of East Anglia in England, heard about a company that wanted to invest in dementia-related research.Having just attended a workshop about gaming in science, he proposed a video game that could help him figure out how people of different ages, genders and locations performed on navigation tasks. Such a game, he thought, could create benchmarks against which to assess patients who might be in the early stages of Alzheimer’s disease.To his surprise, the company — Deutsche Telekom, a major stakeholder in T-Mobile — funded his idea. Known as “Sea Hero Quest,” the smartphone game involved steering a boat to find sea creatures. To recruit players, the company launched an advertising campaign that included a video from PewDiePie, YouTube’s biggest star at the time, who was later penalized by the platform for using antisemitic language.The scientists had hoped that the game would draw 100,000 people in Western Europe. The participants would be testing their navigation skills while also providing basic demographic details, like whether they had grown up in or outside of cities.Instead, over 4.3 million people joined in, generating a global database of clues about people’s ability to get around. “We underestimated the gaming world,” Dr. Hornberger said. “It went beyond our wildest dreams.”For all its simplicity, the game has been shown to predict people’s ability to get around real places, including London and Paris. In recent years, the research team has used the resulting data to show that age gradually erodes people’s navigation skills and that gender inequality is a predictor of whether men will perform slightly better than women. The latest study addressed what its authors described as a more vexing question: Do cities, however grid-like, have the effect of honing people’s navigational skills by offering them a plethora of options for moving around? Or do people from more rural areas, where distances between places are long and paths are winding, develop superior navigation abilities?Ms. de Silva’s childhood in Chicago, a gridlike city, left her struggling to navigate her new home, London.Lyndon French for The New York TimesTo find out, the researchers studied game data from roughly 400,000 players from 38 countries. The effect was clear: People who reported growing up outside cities showed better navigation skills than those from within cities, even when the scientists adjusted for age, gender and education levels.The only situation in which people accustomed to more predictably arranged cities did better was on simpler levels of the video game.Players of varying nationalities performed differently. Urbanites from some places, like Spain, came very close to matching the navigation skills of their rural counterparts. In other nations, like the United States, people raised in cities were at a huge disadvantage.One explanation, the researchers suggested, was that in countries whose biggest cities were complex patchworks, like Spain, chaotic street layouts had sharpened navigation skills. By contrast, nations known for more predictable urban designs, like the United States, put people from outside cities at a bigger advantage.“If you grew up in a city like Chicago or Buenos Aires or Montreal — cities that are very grid-like — you don’t train as much your navigation skills as if you grew up in a more complex city, like London or Paris, where the streets are much more convoluted,” said Antoine Coutrot, a scientist at the French National Center for Scientific Research and another lead author of the paper.To address concerns that people from outside cities were only succeeding because the video game was set in nature, the study’s authors wrote that they replicated the findings in a smaller group of participants recruited to play a different game: “City Hero Quest,” with the same goals but a car in place of a boat.For that experiment, the researchers asked more detailed background questions, including what environment the participants currently lived in. As a result, they were able to learn that people’s present-day surroundings did not significantly affect their performance on the video games.“It really tells you that when your brain is developing, this is the key period,” Dr. Coutrot said. “It’s a bit like when you want to learn a new language.”The study speculated that more complex environments might help new neurons form in the hippocampus, a brain structure important in memory. The authors, though, emphasized that people still were able to develop navigation skills later in life.Some of the authors also noted that street layout was not the only factor making a city harder or easier to navigate. Visible landmarks can be important but are harder to quantify for research purposes than a street network.London’s finanical district and Canary Wharf, a confusing jumble.Hannah Mckay/ReutersThe sea creature game also steered clear of specific questions about people’s locations, professions or how they got around, part of an effort to assuage privacy concerns and keep the science from intruding on the gaming.That hid potentially relevant elements of someone’s upbringing from the research team, even as some commentators remained skeptical of the project on privacy grounds. Among the unknowns was how the Global Positioning System had changed people’s navigational experiences, though Dr. Spiers noted that younger participants produced results similar to those of older people.Outside scientists said that the range and number of participants were far greater than usual.“Lots of different nations are represented, and lots of different types of geographical landscapes are represented,” said Amber Watts, an associate professor of psychology at the University of Kansas who has studied neighborhood layout and cognition but was not involved in the study.Whether the cognitive benefits of more unpredictable city designs were worth the cost of making places more complicated to navigate — including for people already struggling with impairments — was less clear.“Does this mean we should design environments that should be more cognitively challenging?” Dr. Watts said. “If I went to an urban planner and said make it as confusing as possible to get around a city, that’s probably not going to sell well.”Paolo Santi, a research scientist at the Massachusetts Institute of Technology’s Senseable City Lab who was not part of the “Sea Hero Quest” team, said that the results called to mind how he would give directions to tourists in the Italian cities where he grew up.If directions in Manhattan were sometimes as simple as down and over a few blocks, directions in Italian cities had to be more forgiving of grid-minded tourists.“Rather than telling you something you’ll forget, I say to just remember the first part, and when you get there, there are plenty of people to ask again,” he said.Of a place like New York, he said, “On the one hand, you can say the city’s designed well because it’s simplified for the main task, which is getting around. On the other hand, if we don’t challenge ourselves, in a sense we do not fully exploit the potential of our brains.”

Given the surge of Omicron cases in Asia, the new research lends urgency to vaccination campaigns in China and Hong Kong.Two doses of China’s Sinovac vaccine offered older people only a moderately high level of protection against severe disease and death from Covid-19, but a third dose significantly bolstered their defenses, according to a new study by scientists in Hong Kong.The study, based on patients infected during the current devastating Omicron wave in Hong Kong, serves as a cautionary note for mainland China, where Sinovac is a pillar of the country’s vaccination program. Many older people there have yet to receive booster shots.For people 60 and older, two Sinovac doses were 72 percent effective against severe or fatal Covid-19 and 77 percent effective against Covid-related death, the study found. Those levels of protection were lower than those provided by two Pfizer-BioNTech doses. The same study found they were 90 percent effective against severe or fatal Covid and 92 percent effective against death among Hong Kong residents of the same age group.A Sinovac booster shot helped considerably, proving to be 98 percent effective against severe or fatal Covid among people at least 60 years old, the study found.Yanzhong Huang, a global health expert at the Council on Foreign Relations, said that the results highlighted the urgency for mainland China to accelerate its lagging booster campaign. “There’s a lot of work for the government to do to make sure this segment of the population receives the booster shots,” he said.The study’s authors, who are scientists at the University of Hong Kong, noted that the city’s booster program began just recently, making it difficult to determine how long protection from a third dose would last.Because people with underlying health conditions in Hong Kong were more likely to resist getting vaccinated, they said, it was also possible that those who chose to be vaccinated or boosted were healthier in the first place, inflating estimates of how protective the vaccines initially were.Sinovac, a private Chinese company that makes the vaccine, is one of two manufacturers of Covid shots available in China. Vaccines using mRNA technology, like those made by Pfizer-BioNTech and Moderna, are not available there.The new study highlights the potential consequences for China, which has relied heavily on Sinovac and is battling its biggest Covid outbreak in two years. More than 87 percent of China’s population has been vaccinated. But just over half of people 80 and older have had two shots, and less than 20 percent of people in that age group have received a booster, Zeng Yixin, a vice minister of the National Health Commission, said recently.The new study from Hong Kong received funding from the Chinese Center for Disease Control and Prevention as part of what one of the study’s co-authors described this week as an effort to understand the comparative effectiveness of vaccines. It was posted online as a preprint, but has not yet been vetted by peer scientists for publication in a scientific journal.Sinovac’s vaccine performed similarly to Pfizer’s among younger people, even without a booster dose, the study found. In people younger than 60, two Sinovac doses were roughly 92 percent effective against severe or fatal Covid, whereas two Pfizer doses were about 95 percent effective.Coronavirus Vaccine TrackerA look at all the vaccines that have reached trials in humans.Neither vaccine provided very much protection against mild or moderate Covid, though Pfizer’s offered more than Sinovac’s and a booster dose considerably lifted levels of protection. During the latest wave, people in Hong Kong have largely been infected by the subvariant of Omicron known as BA.2. Like other versions of Omicron, BA.2 has infected many vaccinated people.The Hong Kong wave is killing people at a rate exceeding that of almost any country since the coronavirus emerged — a result, in large part, of low vaccination rates among older residents. Almost 90 percent of people who died during the latest wave were not fully immunized, suggesting that getting shots to the most vulnerable is more important than the particular brand of vaccine.Like Hong Kong, mainland China had largely succeeded in tamping down transmission of the virus before Omicron, leaving its population with very little immunity from previous infections.Beyond China, Sinovac vaccines have also been critical in protecting people against severe Covid, especially in poorer countries. The vaccine is being used in 49 countries, including in South America and Africa.But concerns about the protection it offered had already prompted the World Health Organization to recommend in October that recipients 60 and older get a third dose.Dr. Andrew Morris, an infectious disease specialist at Sinai Health and University Health Network in Toronto, who was not involved with the Hong Kong study, said that the results fit with lab studies suggesting that Sinovac generated lower levels of neutralizing antibodies than mRNA vaccines, like Pfizer’s.“I think what we’ll see is in countries that have relied heavily on Sinovac, if they don’t have boosting — especially with an mRNA booster, or even with Sinovac — they’re probably going to struggle with high rates of infection with this latest BA.2 wave,” he said.Dr. Morris said that the results in Hong Kong, like those from other vaccine studies, were also highly dependent on how long it had been since people were administered the shots. Protection tends to weaken over time.The results from the latest study about the effectiveness of third Sinovac doses might be taken as an encouraging sign by Chinese leaders that Chinese-made vaccines could remain the focus of their immunization campaign, said Dr. Huang, of the Council on Foreign Relations.“Now, for the Chinese leaders, they don’t need to face a strong pressure to approve BioNTech’s vaccine,” he said.

As the death toll from Covid-19 surges in Hong Kong, some scientists said that, in the era of Omicron, vaccinating as many older people as possible should be a top priority.Hong Kong, which was once one of the world’s most formidable redoubts of “zero Covid,” has offered scientists a case study about the threat Omicron poses in an entirely different setting: a dense city where people were not only largely untouched by previous infections, but also where the oldest and most vulnerable residents were largely unvaccinated.Several critical lessons emerged, health experts said.With two Omicron subvariants circulating, including the highly contagious BA.2 subvariant, vaccinating a broad swath of the population remained important, scientists said. But inoculating as many older people as possible had become far and away the most critical thing to do.That message, they said, was most pressing for China, where vaccinations in older age groups also appear to be lagging and there is little immunity from earlier infections.But it was relevant again in the United States, too, where subpar vaccination and booster rates among older people have left scientists concerned about a potential surge of BA.2 cases. Partly because so many more Americans have been infected and killed by the coronavirus during earlier waves, scientists do not expect the United States to face as serious a situation in the coming months as Hong Kong.Hong Kong, which along with mainland China had been among the last holdouts of a strategy of tight restrictions and border controls to eradicate the virus, was left vulnerable by how few of its residents had any immunity from prior infections: Before the Omicron surge, scientists estimated that only 1 percent of Hong Kong’s population had contracted the virus.Less than one-quarter of people aged 80 and over in Hong Kong had been given two doses of a vaccine before Omicron surged, compared with more than 90 percent of people in Singapore and New Zealand.The city has now vaccinated 39 percent of residents aged 80 and above, despite having inoculated almost two-thirds of 12- to 19-year-olds.

Covid has surged in a number of Asian countries that had once held the virus at bay. Vaccination levels have largely determined how deadly those waves would be.The first time the Omicron variant breached Hong Kong’s coronavirus defenses, in late 2021, the city stamped it out, cementing its status as one of the world’s most formidable redoubts of “zero Covid.”But a few weeks later, Omicron came to the metropolis again, this time causing an outbreak among cleaners at a public-housing estate that spiraled out of control. The conflagration of resulting cases is now killing people at a rate exceeding that of almost any country since the coronavirus emerged.Over the entire pandemic, Hong Kong’s death toll per capita, once far lower than those of Western nations, is no longer exceptional. A month ago, Americans had died from Covid at 90 times the rate of people in Hong Kong. By Monday, the cumulative American toll was three and a half times as high.As the United States braces for its own, less punishing rise in cases, and mainland China battles its biggest outbreak in two years, scientists have looked to Hong Kong for clues about the threat Omicron poses in an entirely different setting: a dense city where people were not only largely untouched by previous infections, but whose oldest and most vulnerable residents were also largely unvaccinated.Several critical lessons emerged, health experts said.In the era of Omicron and its even more infectious subvariant, BA.2, vaccinating a broad swath of the population remained important, scientists said. But inoculating as many older people as possible had become far and away the top priority.That message, they said, was most pressing for China, where vaccinations in older age groups also appear to be lagging and there is little immunity from earlier infections.But it was relevant again in the United States, too, where subpar vaccination and booster rates among older people have left scientists concerned about a potential surge of BA.2 cases. Partly because so many more Americans have been infected and killed by the coronavirus during earlier waves, scientists do not expect the United States to face as serious a situation in the coming months as Hong Kong.Hong Kong’s dreadful outbreak also signals the perils of trying to eliminate the virus without a plan for what would come next, health experts said. Omicron’s high transmissibility, they said, made outbreaks almost inevitable.Hong Kong, which along with mainland China had been among the last holdouts of a strategy of tight restrictions and border controls to eradicate the virus, was left vulnerable by how few of its residents had any immunity from prior infections: Before the Omicron surge, scientists estimated that only 1 percent of Hong Kong’s population had contracted the virus.A temporary isolation site to house patients with Covid-19 on Tsing Yi Island in Hong Kong.Billy H.C. Kwok for The New York TimesThose low levels of immunity can leave places vulnerable to waves of cases, as more contagious variants sneak in or restrictions are lifted. But governments can still prepare for those waves, said Dr. Gabriel Leung, the dean of medicine at the University of Hong Kong.Less than one-quarter of people aged 80 and over in Hong Kong had been given two doses of a vaccine before Omicron surged, compared with more than 90 percent of people in Singapore and New Zealand.Because of the number of unvaccinated older people in China, scientists said, it might also have some difficulty lifting “zero Covid” restrictions. More than 87 percent of China’s population have been vaccinated. But just over half of people 80 and older have had two shots, and less than 20 percent of people in that age group have received a booster, Zeng Yixin, a vice minister of the National Health Commission, said on Friday.“I don’t think it’s quite ready for the transition,” Dr. Leung said.A number of Asian and Pacific countries had largely kept the virus at bay for two years, only to face Omicron outbreaks because the virus was so contagious and their populations had avoided earlier infections. But high vaccination rates, including among older people, have helped many of those countries avoid more devastating surges.In South Korea, for example, where 87 percent of people are vaccinated and 63 percent have booster shots, the cumulative death toll per capita is one-tenth of America’s, even though South Korea has recorded more than three-quarters as many cases as the United States over the entire pandemic.Health experts said that Hong Kong’s difficulties vaccinating older people resulted from a combination of complacency, given the city’s earlier success in containing the virus, and unfounded fears that older people and those in poor health faced particular risks from vaccines.The city has now vaccinated 39 percent of residents aged 80 and above, despite having inoculated almost two-thirds of 12- to 19-year-olds.Many people in Hong Kong have been given the Chinese vaccine Sinovac, which appears to offer relatively little protection from Omicron infections but a better defense against severe disease. Scientists noted that almost 90 percent of people who died during the latest wave were not fully vaccinated, suggesting that getting shots to the most vulnerable is more important than the particular brand.“The problem in Hong Kong is, we haven’t succeeded in vaccinating our most vulnerable population — the elderly, especially those staying in elderly-care homes,” said Dr. Siddharth Sridhar, a clinical virologist at the University of Hong Kong. “And as a result, we are in a very bad situation.”The United States has vaccinated many more of its older residents than Hong Kong but fewer than Western Europe and has seen a high death rate. And as immunity from early vaccinations wanes and booster shots become critical for shoring up protection against Omicron among older people, the United States finds itself exposed on that count, too. About 41 percent of people 65 and over have not received a booster shot.Unlike other parts of Asia that had gradually lifted restrictions in recent months, Hong Kong was not ready for its defenses to fail, scientists said.“From the government’s point of view, there was such a strong fixation on ‘zero Covid’ that as long as that worked, vaccination was not necessarily the priority,” said Ben Cowling, a professor of epidemiology at the University of Hong Kong.Many older residents and their families adopted the same view, public health experts said. If Hong Kong’s rigid social-distancing measures and careful border controls were going to keep the virus out anyway, the conventional thinking went, was getting a vaccine worth the trouble?“If you’re telling people that the disease is never going to get in, then there’s less of an incentive to go and get vaccinated,” said Dr. David Owens, a family doctor in Hong Kong. “To an extent, the messaging around elimination confounded the need to vaccinate.”People waiting to be tested for the coronavirus in Tsing Yi, which was placed under lockdown this month.Billy H.C. Kwok for The New York TimesDr. Cowling, of the University of Hong Kong, said that his city could have responded in one of two ways to signs that cases would surge: either double down on “zero Covid” through measures like building better quarantine facilities for overseas arrivals, or acknowledge that outbreaks are unavoidable and raise vaccination rates.“Zero Covid is a really good strategy if you can stay at zero,” Dr. Cowling said. “But as we found in Hong Kong, it doesn’t last forever.”Hong Kong eventually took steps to persuade older people to become vaccinated, once earlier inducements like vaccine passes proved ineffective. In January, the government announced that it would ban unvaccinated people from restaurants that serve dim sum, which are popular among older residents. But it was too late.With cases and deaths now declining, Hong Kong announced on Monday that it would lift certain restrictions.Singapore began abandoning “zero Covid” policies in the summer. Dr. Ooi Eng Eong, an infectious disease expert at Duke-National University of Singapore Medical School, said that it took a wave of the Delta variant to raise vaccination rates and disabuse people of the notion that they did not need protection.Now, cases in Singapore have surged, but deaths are relatively low.“It’s so much more transmissible that I think wearing a face mask and all — that helps but not to the extent that it has impacted the epidemiology,” Dr. Ooi said of Omicron. “The trends are really driven by vaccination.”Still, even after five or six waves of the pandemic, the reasons that some countries have succeeded while others have suffered remain unclear.Japan, for example, has tamped down on cases throughout the pandemic without resorting to full-fledged lockdowns, scientists said.The country benefited from its government sharing sound publichealth advice early in the pandemic. As much as residents tired of precautions, they largely took the advice seriously, said Taro Yamamoto, a professor at the Institute of Tropical Medicine at Nagasaki University.Roughly 80 percent of people in Japan have had their initial vaccine series. But even though the country is lagging in administering booster doses and had a surge of Omicron infections, death rates during Omicron have remained considerably lower than in nearby South Korea.“Partly it’s a mystery,” Professor Yamamoto said. “We cannot explain it all.”

More and more American school districts have dropped mask mandates in recent weeks as coronavirus cases plunged across the United States. But they remain a subject of debate among some students and their parents, and a study released on Tuesday by the Centers for Disease Control and Prevention suggested that those mandates had helped protect children and teachers from the coronavirus last fall.The study, examining public school districts in Arkansas from August to October as the Delta variant spread, found that districts with full mask requirements had 23 percent lower rates of the coronavirus among students and staff members than districts without the mandates.It was not clear whether the same would have been true once the Delta variant was overtaken by Omicron, which is more contagious and spread rapidly among children and adults alike.The C.D.C. has faced criticism from scientists in the past for overstating the benefits of school masking based on what some researchers have described as a flawed study out of Arizona. Some studies from abroad have also found that mask mandates were not associated with lower rates of the coronavirus in children.But some scientists said that the latest C.D.C. study had steered clear of the most serious methodological problems and had strengthened the evidence for masks protecting some children from the coronavirus.“It passes the smell test,” Louise-Anne McNutt, a former C.D.C. Epidemic Intelligence Service officer and an epidemiologist at the State University of New York at Albany, said of the study. “The estimates of the impact of masks are consistent with other studies that show masks have a modest, but important, reduction of SARS-CoV-2 transmission.”The study compared coronavirus case rates among 233 Arkansas districts. About a third of the districts had full mask mandates, a fifth required masks only in certain settings or situations, and half had no mask policies.It took into account staff and student vaccination rates and socioeconomic status. It also adjusted for coronavirus rates in the surrounding community — an attempt, the study’s authors said, to partly control for how much testing was happening in a given part of the state. Dr. McNutt, though, said that the study would have benefited from more details on statewide testing levels.Districts with full mask mandates had lower coronavirus rates relative to the case rates in the surrounding community than districts without the mandates, the study found. And among roughly two dozen districts that put in place mask mandates in the middle of the study period, case rates afterward dropped more than would have been expected from changes in community case rates at the same time, the study said.Partial masking policies did not show as strong an effect as full mask mandates.The study did not account for schools’ prevention efforts beyond masking, like ventilating classrooms. Jonathan Ketcham, an economist specializing in health care at Arizona State University, said that could be an “important flaw in the study itself.”Jason Abaluck, an economics professor at Yale University’s School of Management who helped lead a large trial on masking in Bangladesh, also cautioned that the schools with mask mandates could have differed from those without them in other ways, like adherence to distancing measures. He said that the study could have more closely matched nearby schools with different masking policies to study their effects.But Dr. Abaluck said the C.D.C. study was an improvement on previous research.“This study and the broader literature on masking suggests that in places where hospitalization and deaths are very high, the benefits of mask wearing in schools may be considerable,” he said.Still, he noted that masks can cause discomfort and make it harder for children to communicate. “Figuring out how severe an outbreak has to be to warrant mask mandates in schools,” he said, “requires making best guesses about the costs, which remain highly uncertain given existing evidence.”

A funding dispute with Republican senators may complicate the Biden administration’s efforts to guarantee supplies of free antiviral pills and monoclonal antibody treatments this year to Americans who test positive for the coronavirus.At issue is whether the White House has provided the level of detail desired by Republicans about the trillions of dollars in Covid relief spending that Congress previously authorized. A group of three dozen Republican senators, led by Mitt Romney of Utah, told the White House last week that they would not consider billions in new Covid relief spending without a more detailed accounting of how existing funds had been spent and whether any money was left over.“It is not yet clear why additional funding is needed,” they wrote in a letter to President Biden on Wednesday.Administration officials have requested $22.5 billion for additional vaccines, oral antivirals and monoclonal antibodies, testing and support for the global vaccination effort.Republican senators have suggested that the administration should divert money from the $1.9 trillion pandemic law to the areas of need, rather than have Congress spend billions of new funds.Jen Psaki, the White House press secretary, said on Friday that the current supply of monoclonal antibodies will run out by May and stocks of oral antivirals would be depleted by September without new purchases. “This is an urgent request,” she said.A breakdown of spending on Covid-related supplies like testing, vaccines and treatments provided to Congress by the Biden administration and obtained by The New York Times indicated that nearly all existing funds had been spent or committed in signed contracts, and that any remaining funds had been allocated. The administration offered some detail on its plans for new Covid spending in a letter to Congress on Wednesday.The funding dispute is playing out as the White House tries to put in place plans that it says are essential to the country’s efforts to return to a semblance of normalcy.Hundreds of pharmacies and other health facilities were prepared to launch a “test to treat” program this week allowing people to walk in for a coronavirus test and, if the results are positive, to leave with free antiviral pills, administration officials said.Last week, the Department of Defense told STAT, a medical news outlet, that it would exercise contract options to buy more of Pfizer’s antiviral treatment, known as Paxlovid, once funding became available.The White House also said that Americans who had already received a package of four free at-home coronavirus tests from the government would become eligible this week to place a second order on covidtests.gov.New virus cases in the United States have plunged in recent weeks, but more than 1,500 Americans are still dying from the virus each day on average.There are also signs that a particular version of the Omicron variant that is even more contagious than the one that tore through the United States this winter is becoming more prevalent, rising to roughly 8 percent of sequenced cases in the United States by late February. But overall cases remain on the decline and vaccines look to be equally effective against the Omicron subvariant, which does not appear to be any more severe.Biden administration officials hope to include the $22.5 billion in coronavirus aid, alongside humanitarian and military aid for Ukraine, in a sprawling catchall spending package that would fund the government for the remainder of the fiscal year. Congress has until March 11, when funding is set to lapse, to hammer out the details of a deal.

The Omicron variant of the coronavirus has been so contagious that it may have seemed a foregone conclusion that if one person in a household became ill, other people living there would catch the virus, too.But that turns out to be less certain: A small study of households by the Centers for Disease Control and Prevention released on Friday found that when the first person infected wore a mask and stayed in a separate room at least part of the time, the risk of other household members contracting the virus became markedly lower.Vaccinated people who became infected were also considerably less likely than unvaccinated people to spread the virus to other members of their households.Still, the study highlighted just how aggressively the Omicron variant had spread within a home, especially among people living with children under 5 who tested positive. Those children, who are not yet eligible for vaccines and often need to be in closer contact with their parents or relatives, spread the virus to 72 percent of household contacts identified in the study — the highest rate of any age group, the C.D.C. said.“These findings further highlight young children’s potential contribution to household transmission,” C.D.C. scientists wrote in the report.Federal regulators are waiting for data on how well three doses of the Pfizer-BioNTech coronavirus vaccine work in children under 5 before deciding whether to authorize the vaccine for that age group.The C.D.C. study was based on 183 households across four states where someone became infected with the Omicron variant from November to early February. After interviewing members of the households about their vaccination and infection histories, any precautionary measures in the home and whether they had tested positive or become ill, C.D.C. scientists determined that the variant had spread in roughly two-thirds of the households they identified.But when the first infected person was fully vaccinated, only about 44 percent of household members developed Covid, compared with 64 percent when the infected person was unvaccinated, the study said.And when the original infected household member stayed in a room alone at least some of the time, only 41 percent of other members of the household became infected, compared with 68 percent in situations without isolation. Masking by the infected person helped, too, reducing the likelihood of transmission to 40 percent from 69 percent.Determining the precise risk of the virus spreading in a home was difficult, the study’s authors noted. They excluded situations where it was unclear who had first developed Covid, and did not do the genetic sequencing necessary to know for certain that people had caught the virus from the infected person in their home rather than at other gatherings.

After the first person known to have become infected with the Omicron variant in the United States was revealed to have attended a 53,000-person anime convention in Manhattan, concerns quickly mounted that the event had sown the seeds of a major coronavirus outbreak.But a new study released on Thursday by the Centers for Disease Control and Prevention suggested that a combination of good air filtration, widespread vaccination and indoor masking had in fact helped prevent the anime convention in November from becoming a superspreader event.The share of attendee tests that came back positive was similar to the share of coronavirus tests that were positive across New York City around the same time, the C.D.C. said. What’s more, the few positive samples that were genetically sequenced were largely of the Delta variant, not Omicron.And conventiongoers who became infected were more likely than those who tested negative to have gone to bars, nightclubs or karaoke clubs.Still, the C.D.C. said that the virus’s spread at the convention could have been much worse had it been held after Omicron became dominant in the city, given that the variant is so contagious and capable of spreading among the vaccinated. At the anime convention, the C.D.C. said in a separate report on Thursday, the only documented Omicron infections were in a single cluster of at least 16 positive cases.The first study relied largely on people who came forward for testing after the event, which introduced potential biases: Those people could have been more cautious than the average convention attendee, or more inclined to report cautious behaviors. Health officials had urged attendees to get tested. The C.D.C. could only look for cases among people on a registration list of ticket buyers, which did not account for the full number of attendees.The agency’s findings matched those of New York City contact tracing officials, who said in early December that they had not found signs of widespread transmission at the anime convention.In the aftermath of the event, held at the sprawling Javits Center, the convention organizers came under scrutiny as people reported seeing attendees flouting masking rules and pushing past checkpoints.But among attendees who were tested, the C.D.C. said, “evidence of widespread transmission during the event was not identified.”The study drew on test results identified through health department surveillance systems for 4,560 attendees. Of those, 119 people — 2.6 percent — tested positive. Researchers also sent online surveys to attendees asking about their test results, symptoms and activities during the convention.The anime convention required attendees to have received at least one vaccine dose. The C.D.C. said that among attendees who could be matched with test and vaccination data in health department surveillance systems, 85 percent had completed their primary vaccination series, another 12 percent had received a booster dose and 3 percent were partly vaccinated.The C.D.C. study also credited the convention hall for being outfitted with HEPA filters, which have been shown to efficiently remove coronavirus particles from the air.

Such an extensive head injury would likely have left the actor confused, if not unconscious, experts said.Bob Saget, the comedian and actor, died after what appeared to be a significant blow to the head, one that fractured his skull in several places and caused bleeding across both sides of his brain, according to an autopsy report released on Friday.The findings complicated the picture of Mr. Saget’s death that has emerged in recent days: Far from a head bump that might have been shrugged off, the autopsy described an unmistakably serious set of injuries that would at the very least have probably left someone confused, brain experts said.The report, prepared by Dr. Joshua Stephany, the chief medical examiner of Orange and Osceola counties in Florida, ascribed Mr. Saget’s injuries to a fall.“It is most probable that the decedent suffered an unwitnessed fall backwards and struck the posterior aspect of his head,” Dr. Stephany wrote, referring to the back of the skull.Still, the autopsy left a number of unresolved questions about how exactly Mr. Saget, 65, was so badly hurt. He was found dead in a hotel room at the Ritz-Carlton Orlando, Grande Lake on Jan. 9 during a weekend of stand-up comedy acts. His family said this week that the authorities determined that he had hit his head, “thought nothing of it and went to sleep.”If the actor struck his head hard enough, and in just the wrong place, it is possible that fractures would have extended to other parts of his skull, brain injury experts said. Situations where someone cannot break their fall are even more dangerous.“It’s like an egg cracking,” said Dr. Jeffrey Bazarian, an emergency physician and concussion expert at the University of Rochester Medical Center. “You hit it in one spot, and it can crack from the back to the front.”But experts said that with such an extensive injury, it was unlikely that Mr. Saget would have intentionally ignored it. The injury would likely have left him confused, if not unconscious.“I doubt he was lucid,” Dr. Bazarian said, “and doubt he thought, ‘I’m just going to sleep this off.’”Some neurosurgeons said that it would be unusual for a typical fall to cause Mr. Saget’s set of fractures — to the back, the right side and the front of his skull. Those doctors said that the injuries appeared more reminiscent of ones suffered by people who fall from a considerable height or get thrown from their seat in a car crash.The autopsy, though, found no injuries to other parts of Mr. Saget’s body, as would be expected in a lengthier fall. The medical examiner ruled that the death was accidental. The local sheriff’s office had previously said there were no signs of foul play.“This is significant trauma,” said Dr. Gavin Britz, the chair in neurosurgery at Houston Methodist. “This is something I find with someone with a baseball bat to the head, or who has fallen from 20 or 30 feet.”Dr. Britz noted that the autopsy described fractures to particularly thick parts of the skull, as well as to bones in the roof of the eye socket. “If you fracture your orbit,” he said, referring to those eye bones, “you have significant pain.”The knock ruptured veins in the space between the membrane covering the brain and the brain itself, causing blood to pool, the autopsy indicated. The brain, secured in a hard skull, has nowhere to move, doctors said, and the result is a compression of brain centers critical for breathing and other vital functions.No alcohol or illegal drugs were detected in the actor’s system, according to the autopsy. But there were signs of Clonazepam, commonly known as Klonopin, a benzodiazepine that is used to prevent seizures and treat panic attacks. Tests also found Trazodone, an antidepressant, the report said.There was no indication in the autopsy findings that either of those drugs might have contributed to Mr. Saget’s injuries. But doctors said that they could make people sleepy and contribute to a fall.Benzodiazepines are widely prescribed for older people, despite warnings about the side effects. People who take them face increased risks of falls and fractures, of auto accidents and of reduced cognition.Use of multiple drugs “is a very dangerous cause of falls in the elderly,” said Dr. Neha Dangayach, the director of neuro-emergencies management and transfers for the Mount Sinai Health System. She said that some combinations could cause drops in blood pressure or confusion.The report noted that Mr. Saget had an enlarged heart, but did not suggest any link to his death. It also found signs of the coronavirus on a PCR test, but did not suggest that the virus contributed to Mr. Saget’s death. The actor said on a podcast in early January that he had contracted the virus, without specifying exactly when. PCR tests can show the presence of the virus days or even weeks after someone has recovered.Mr. Saget, best known for his role on the sitcom ‘Full House’ and for hosting ‘America’s Funniest Home Videos,’ thanked the “appreciative audience” of his stand-up comedy set in a Tweet early in the morning on Jan. 9, the day of his death.“I had no idea I did a 2 hr set tonight,” he said. “I’m happily addicted again to this.”