Falling numbers of mpox cases across Africa last week led the World Health Organization (WHO) to decide the continent’s epidemic of the debilitating and sometimes deadly viral disease no longer warrants emergency status. Mpox frequently moves from wild animals, likely rodents, to humans, but in the past, outbreaks usually occurred in remote areas and quickly died out. Today, mpox increasingly moves from person to person with ease, causing sustained spread, and the virus has found its way to urban areas. Cases exploded in Africa in the summer of 2024, causing WHO in August 2024 to declare the surge a Public Health Emergency of International Concern (PHEIC), its highest level of alarm. Only four other diseases have merited PHEIC status. But over the past few months, new mpox cases have decreased, leading WHO Director-General Tedros Adhanom Ghebreyesus to announce on 5 September that he was ending the PHEIC, as recommended by an advisory committee. SIGN UP FOR THE AWARD-WINNING SCIENCEADVISER NEWSLETTER The latest news, commentary, and research, free to your inbox daily Sign up Tedros noted that the countries with the highest numbers of cases—including the Democratic Republic of the Congo (DRC), Burundi, Sierra Leone, and Uganda—have seen sustained declines. “We also have a better understanding of the drivers of transmission, the risk factors for severity, and the most affected countries have developed a sustained response capacity,” he said. An emergency committee convened by the Africa Centres for Disease Control and Prevention (Africa CDC), in contrast, last week unanimously urged that what it calls a Public Health Emergency of Continental Security remain in place. Africa CDC’s director, Jean Kaseya, promptly accepted that recommendation. Testing for the virus that causes mpox is spotty, but Africa has recorded more than 32,000 confirmed cases this year and more than 100,000 suspected ones. Mpox causes painful blisters and, particularly in young children or adults with damaged immune systems, can lead to death. For decades, the DRC was the only country that had major outbreaks, but in 2022, the virus started to spread explosively around the world, mainly among men who have sex with men, which triggered the first PHEIC for mpox. It ended in May 2023, after the use of mpox vaccines and education campaigns led to sharp drops in cases. Advertisement A few months later, a rarely seen variant of mpox began to spread among women sex workers and their men clients in Kamituga, a mining town in the DRC. By August 2024 the virus had jumped borders and infected children and adults in several neighboring countries that had never seen the disease before. African countries scrambled to obtain and deliver mpox vaccines, but the supply has fallen far short of what Africa CDC projected what was needed. To date, roughly 1 million vaccine doses have been administered in 12 African countries. Two million additional doses have been delivered to countries but have yet to reach people in need of protection. “Of course, lifting the emergency declaration does not mean the threat is over, nor that our response will stop,” Tedros said on Friday. Africa CDC noted that case numbers for the continent in July and August have indeed dropped by 52% compared with April and May. But the agency remains seriously concerned. “New countries such as Liberia, Ghana, and Guinea are now emerging [as mpox hot spots] and need urgent attention—especially around surveillance, lab decentralization, and vaccination,” says epidemiologist Yap Boum, who heads the mpox response for Africa CDC. Boum says he is concerned about people living with HIV, who are especially vulnerable to other infectious diseases. Cuts in foreign assistance by the United States and other countries have reduced access to anti-HIV medication in sub-Saharan African countries, making this large population even more likely to suffer life-threatening complications from mpox, he says. Africa CDC will review whether to keep the continental emergency declaration in place in 3 months.

LISTEN TO THIS ARTICLE Play Pause Skip backwardsGo ten seconds backward Skip forwardsGo ten seconds forward Progress 1.0x Mute Unmute Volume is at 50% 00:00 2:26 1.0x Audio is AI-generated. Report an issue | Give feedback Relative to their bodies, the sperm of male fruit flies are gigantic. Thanks in part to female fruit flies’ preference for long sperm, the sperms of some male fruit flies have evolved to become 1.8 millimeters long, about as long as they are. This poses unusual storage challenges: The flies stuff thousands of sperm into storage sacs that are each just 200 microns wide. What happens physically when so many of them are squished into a tight space? In a recent arXiv preprint, researchers report this mass of sperms collectively flows around the sacs they are stuffed in—their movement stretching them out in a way that could prevent them from tangling up. Unlike human sperms, fruit fly sperms don’t swim around well; they can only wriggle in place. But when they are packed together, this behavior changes. Using mathematical modeling and fluorescence microscopy, a team led by researchers Jasmin Imran Alsous and Brato Chakrabarti found that within the confined space of a storage sac, the sperms propel themselves forward off neighbors that are going the opposite way. “When we swim, we push fluid back, and the fluid provides us momentum to move forward, [but here], they push off from one another,” explains Chakrabarti, a physicist at India’s International Centre for Theoretical Sciences. Senior study author Michael Shelley, a mathematician at New York University and the Flatiron Institute, likens the mass to “a thousand-lane highway, where every other lane, somebody’s going in opposite directions and the lanes are constantly moving around.” SIGN UP FOR THE AWARD-WINNING SCIENCEADVISER NEWSLETTER The latest news, commentary, and research, free to your inbox daily Sign up The new study sheds light on how male flies keep their sperm unentangled, a factor that could affect insect fertility. As the fruit fly sperms push past each other, the flagella of neighboring sperm get stretched out, which could help the sperms align with each other and remain tangle-free, the researchers think. If the sperms were entangled, none of them would be able to exit the male flies smoothly during mating, rendering the flies sterile. “[In] the textbook picture, there’s always this one sperm shown as the fastest, best sperm that makes it,” says Alsous, a scientist at the Flatiron Institute. “In this case, their interactions with each other are key for any of them surviving.”

LISTEN TO THIS ARTICLE Play Pause Skip backwardsGo ten seconds backward Skip forwardsGo ten seconds forward Progress 1.0x Mute Unmute Volume is at 50% 00:00 05:30 1.0x Audio is AI-generated. Report an issue | Give feedback Controversial “geoengineering” proposals to cool a warming planet often involve blocking sunlight with aerosols, brightening clouds over the oceans, or pulling carbon dioxide from the air and locking it up underground. Now, a pair of researchers is proposing a radical new geoengineering scheme—one that would unfold not in the skies, but in the seas. The goal wouldn’t be to cool the planet, but to avert a paradoxical—and so far hypothetical—consequence of warming. To address persistent fears that the conveyor belt of currents in the Atlantic Ocean responsible for Western Europe’s mild climate could suddenly collapse as the climate warms, the researchers say society should explore the idea of building a dam across the Bering Strait, the 80-kilometer-wide gap between Siberia and Alaska. Paleoclimate evidence suggests these currents—the Atlantic Meridional Overturning Circulation, or AMOC—were stronger during a past ice age, when seas were lower and a Bering Strait land bridge severed the Arctic Ocean from the Pacific Ocean. A simple modeling experiment, posted as an arXiv preprint last week, suggests artificially re-creating that land bridge today could bolster the AMOC. Jelle Soons, a doctoral student at Utrecht University who led the work with Henk Dijkstra, a physical oceanographer, says that given the potential vulnerability of the AMOC, the idea is worth considering. “The risk of collapse is certainly not negligible.” SIGN UP FOR THE AWARD-WINNING SCIENCEADVISER NEWSLETTER The latest news, commentary, and research, free to your inbox daily Sign up Other researchers say much more analysis needs to be done before the proposal should be taken seriously. “The feedbacks and consequences of this are enormous and enormously unknown,” says Susan Lozier, an oceanographer at the Georgia Institute of Technology. A massive barrier between oceans could affect other currents, along with wildlife and society. A bigger concern is that other climate modeling studies, conducted more than a decade ago, show closing off the Bering Strait could doom the AMOC, not save it. Researchers don’t agree on how much of a threat global warming poses to the AMOC, and so far it shows little sign of weakening, Lozier says. “Climate models that predict tipping points have no validation.” But climate scientists see two ways global warming could stall the AMOC, which carries dense salty waters from the tropics to the North Atlantic, where they cool and sink to the abyss. Direct warming of North Atlantic waters could prevent the saline waters from cooling and sinking. But so, too, could melting ice sheets, because they add lighter weight freshwater to the mix. Soons’s modeling study added freshwater to the North Atlantic but placed more of an emphasis on its rapid warming. Under this scenario, relatively fresh water from the North Pacific added to the pressure on the AMOC. The water passed through the Bering Strait, eventually ending up in the North Atlantic and shutting down the currents. Blocking the strait with a dam helped them survive. Advertisement But earlier, more detailed modeling by Aixue Hu, an oceanographer at the National Center for Atmospheric Research, had shown the opposite effect. Hu focused on freshwater added to the North Atlantic and found that some of it flows north into the Arctic, where it escapes through the Bering Strait into the Pacific. In effect, the strait serves as a safety valve, helping the AMOC stay salty and survive. With the strait closed, he found, this freshwater instead accumulates in the Arctic, until it eventually flows back into the Atlantic, causing the AMOC’s sudden collapse. Other modelers have seen similar effects. “It’s an interesting idea,” Hu says of Soons’s scheme. “But in reality, it could cause the potential problem they are trying to avoid.” A simplified view of the Atlantic Meridional Overturning Circulation, which ferries warm water to Western Europe before cooling and sinking to the ocean floorMIKKEL JUUL JENSEN/SCIENCE PHOTO LIBRARY Actually building such a dam is more feasible than one might expect, Soons says. At the Bering Strait’s narrowest point, Russia and Alaska are closer than Philadelphia and New York City. The strait’s maximum depth is 59 meters, and two small islands sit smack in the middle. The largest similar structure, the Saemangeum Seawall in South Korea, is 33 kilometers long and up to 54 meters deep. It cost nearly $3 billion to build by the time of its completion in 2010—less than a three-station subway extension in New York City. On the other hand, the South Korean seawall was built in placid coastal waters, not in rough, remote waters frequently choked with sea ice and bordered on each side by fierce geopolitical rivals. A dam would surely cause many other problems. Marine mammals pass through the strait seasonally, as do many fish species; the region is also a refuge for subarctic species expanding into the Arctic as oceans warm. Disrupting this wildlife would likely impact Indigenous communities dependent on it for food and trade. And the dam could impede growing ship traffic through the strait, Soons says. Soons is testing the same scenarios in a more advanced climate model. For now, these findings should be taken with a grain of salt, Hu says. “This work alone cannot convince us to do this.” And if Hu was dreaming up AMOC geoengineering schemes, he says, he might instead suggest salting the North Atlantic directly, to keep it dense. Of course, Soons adds, the best way to address the problem would be to slow global warming by reducing the burning of fossil fuels.

LISTEN TO THIS ARTICLE Play Pause Skip backwardsGo ten seconds backward Skip forwardsGo ten seconds forward Progress 1.0x Mute Unmute Volume is at 50% 00:00 03:35 1.0x Audio is AI-generated. Report an issue | Give feedback The U.S. Department of State announced yesterday it will honor a commitment made before President Donald Trump took office to help millions of people in poor countries receive a powerful new HIV prevention tool. A single shot of the anti-HIV drug lenacapavir can protect a person from the virus for 6 months, meaning it can be easier to deploy than commonly used prevention drugs, which require a person to take a pill every day. Many researchers believe expanding the use of lenacapavir would help reduce the 1.3 million new infections in the world each year—if people can obtain it. In December 2024, the U.S. President’s Emergency Plan for AIDS Relief (PEPFAR) said it would join with the Global Fund to Fight AIDS, Tuberculosis and Malaria and others to pay for at least 2 million people living in countries with lower incomes to access this form of pre-exposure prophylaxis (PrEP) over 3 years. But the Trump administration then dismantled much of PEPFAR, putting a giant question mark over this pledge. SIGN UP FOR THE AWARD-WINNING SCIENCEADVISER NEWSLETTER The latest news, commentary, and research, free to your inbox daily Sign up Now, the State Department say it is negotiating agreements that may lead to the United States providing the promised doses of lenacapavir in as many as 12 still-to-be-identified countries. “We’re very excited to help support this medication,” Jeremy Lewin, a State Department official, said at a press conference yesterday. He said the countries would be decided within “the next few weeks.” Other forms of PrEP have fallen short because many people—particularly young women and girls in sub-Saharan Africa—have had difficulty taking a daily pill. In contrast, lenacapavir PrEP can be given as one shot every 6 months and has shown remarkably high levels of efficacy in clinical trials. (Science selected it as the Breakthrough of the Year in 2024.) Over the past 3 months, lenacapavir has received regulatory approval in the U.S. and Europe. Now, lenacapavir PrEP will be rolled out to poorer countries in lockstep with it first becoming available in the U.S., says Jirair Ratevosian, a former PEPFAR chief of staff who now does global health security research at Duke University. “That rarely happens in global health, and it deserves recognition,” he says. But he also says the stated goal of providing the drug to 2 million people over 3 years is “timid,” and by itself unlikely to make much of a dent in the global epidemic. “Setting the bar so low risks repeating old mistakes—where innovation trickles down slowly, unevenly, and inequitably,” he says. (Lewin said the 2 million doses is “just the floor” of what the U.S. government will provide.) Advertisement The Trump administration wants to limit the rollout to pregnant and breastfeeding people, Lewin said, explaining that Trump hopes to end mother-to-child transmission by the time his term ends in 2029. But Lewin noted that although it’s “our strong recommendation” that the shots go to these women, “there’s no formal restriction” that prohibits others from receiving the drug with the PEPFAR-supported program. Gilead Sciences, the maker of lenacapavir, is selling the drug for this effort at no profit, but has not revealed the discounted price. The company has also made deals with six generic companies to produce and sell the drug to low- and middle-income countries, but it will take an estimated 2 years before those products become available.

Harvard University scored a major victory in its battle against President Donald Trump’s administration yesterday, as a federal judge ruled the government broke the law when it cut billions of dollars in research grants to the school. The decision has inspired some optimism among scientists. But the White House is already vowing to appeal, signaling that Harvard’s fight to regain its funding is far from over. “While this is an important legal victory, there are many steps to go,” says David Walt, a researcher at Harvard Medical School and Brigham and Women’s Hospital. When the Trump administration in April froze funds to Harvard, he was told to immediately stop work on his project studying diagnostics and treatments for amyotrophic lateral sclerosis. Although Walt is “delighted” by the new ruling, he notes that “the only way we will be able to restart the project is when funds arrive from the feds.” Some Harvard researchers, meanwhile, have already begun to close labs and lay off staff. The funding fight began in April, when the Trump administration accused Harvard of failing to address antisemitism on campus and demanded the university change its hiring and teaching practices and grant the government control of some operations. After Harvard refused to comply, the federal government froze—and later terminated—nearly $2.2 billion in research grants to the university. SIGN UP FOR THE AWARD-WINNING SCIENCEADVISER NEWSLETTER The latest news, commentary, and research, free to your inbox daily Sign up In an 84-page ruling, U.S. District Court Judge Allison Burroughs found those actions violated Harvard’s First Amendment rights. The administration, she wrote, “used antisemitism as a smokescreen for a targeted, ideologically-motivated assault on this country’s premier universities.” The ruling “is very vindicating” for those who believed the terminations were unjustified, says Harvard epidemiologist and former attorney Scott Delaney, whose research on how environmental factors such as pollution and extreme heat affect people with Alzheimer’s and Parkinson’s diseases ground to a halt after the funding cutoff. Delaney, who created a database to track cancellations of grants from the National Institutes of Health (NIH), wasn’t surprised by the decision. “Harvard always had a strong case,” he argues. “The government’s conduct was blatantly illegal.” Delaney hopes the ruling will inspire other universities targeted by the Trump administration to continue to fight back, rather than capitulate to the government’s demands. In July, Columbia University agreed to pay more than $200 million in order to unfreeze its NIH funding—a decision that drew mixed reactions from researchers. A few days later, Brown University reached a similar settlement, in which the school agreed to hand over data on admissions and diversity efforts, and not to perform gender-affirming treatments on minors, among other concessions. These institutions “lost a lot,” Delaney argues, “and not just money.” Advertisement Harvard was said to be open to a settlement, reportedly to the tune of $500 million. But university President Alan Garber told faculty in August that such a deal was not imminent. The government will likely appeal yesterday’s decision to the First Circuit Court of Appeals, which Delaney says will probably uphold it. After that, the case is probably headed for the U.S. Supreme Court, where the outcome is far less certain. Last month, the justices upheld the termination of hundreds of NIH grants. The uncertainty leaves some researchers doubting funding will be soon restored. It’s already too late for some projects, such as FlyBase—a key database for fruit fly genetics that lost its funding because of the Harvard freeze. A few weeks ago, Harvard informed the FlyBase team that eight of its staff would be laid off. Even if funding is ultimately restored, Walt notes that certain labs will have a much harder time getting back on track than others. For some studies, “particularly those that involved patients who were being treated and followed, there will be no chance to recover from the funding gap without starting over completely.” Any restoration of funding will also come too late for Delaney, who was laid off after the grants that supported his salary were terminated. “I had no plans to leave. I love my job,” he says. But in his view, yesterday’s ruling still represents a major victory—for both the rule of law and for science. “Even if folks like me won’t be around to do the research, most of my colleagues will be, and they’re still as good and productive as they ever have been.” “I’m cautiously optimistic that some of the funds might eventually be reinstated, but there’s still a ways to go before that becomes a reality,” says Harvard neuroscientist Samuel Gershman. Even if Harvard ultimately prevails in court, he is concerned that the government will find other ways to disrupt research at the university. The White House has, for example, attempted to block Harvard from enrolling international students, and Trump has threatened to revoke Harvard’s tax-exempt status. Fighting back against this administration, Gershman adds, can feel like “a game of Whac-A-Mole.” But despite these obstacles, Gershman still thinks Harvard should avoid a settlement: “In the big picture, it’s more important that the university protect itself from political interference and retain its status as a haven for independent intellectual thought.”