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Tag: immune defenses

  • One More COVID Summer?

    One More COVID Summer?

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    Since the pandemic’s earliest days, epidemiologists have been waiting for the coronavirus to finally snap out of its pan-season spree. No more spring waves like the first to hit the United States in 2020, no more mid-year surges like the one that turned Hot Vax Summer on its head. Eventually, or so the hope went, SARS-CoV-2 would adhere to the same calendar that many other airway pathogens stick to, at least in temperate parts of the globe: a heavy winter peak, then a summer on sabbatical.

    But three and a half years into the outbreak, the coronavirus is still stubbornly refusing to take the warmest months off. Some public-health experts are now worried that, after a relatively quiet stretch, the virus is kick-starting yet another summer wave. In the southern and northeastern United States, concentrations of the coronavirus in wastewater have been slowly ticking up for several weeks, with the Midwest and West now following suit; test-positivity rates, emergency-department diagnoses of COVID-19, and COVID hospitalizations are also on the rise. The absolute numbers are still small, and they may stay that way. But these are the clear and early signs of a brewing mid-year wave, says Caitlin Rivers, an epidemiologist at Johns Hopkins University—which would make this the fourth summer in a row with a distinct coronavirus bump.

    Even this far into the pandemic, though, no one can say for certain whether summer waves are a permanent COVID fixture—or if the virus exhibits a predictable seasonal pattern at all. No law of nature dictates that winters must come with respiratory illness, or that summers will not. “We just don’t know very much about what drives the cyclical patterns of respiratory infections,” says Sam Scarpino, an infectious-disease modeler at Northeastern University. Which means there’s still no part of the year when this virus is guaranteed to cut us any slack.

    That many pathogens do wax and wane with the seasons is indisputable. In temperate parts of the world, airborne bugs get a boost in winter, only to be stifled in the heat; polio and other feces-borne pathogens, meanwhile, often rise in summer, along with gonorrhea and some other STIs. But noticing these trends is one thing; truly understanding the triggers is another.

    Read: COVID sure looks seasonal now

    Some diseases lend themselves a bit more easily to explanation: Near the equator, waves of mosquito-borne illness, such as Zika and Chikungunya, tend to be tied to the weather-dependent life cycles of the insects that carry them; in temperate parts of the world, rates of Lyme disease track with the summertime activity of ticks. Flu, too, has pretty strong data to back its preference for wintry months. The virus—which is sheathed in a fragile, fatty layer called an envelope and travels airborne via moist drops—spreads best when it’s cool and dry, conditions that may help keep infectious particles intact and spittle aloft.

    The coronavirus has enough similarities to flu that most experts expect that it will continue to spread in winter too. Both viruses are housed in a sensitive skin; both prefer to move by aerosol. Both are also relatively speedy evolvers that don’t tend to generate long-lasting immunity against infection—factors conducive to repeat waves that hit populations at a fairly stable clip. For those reasons, Anice Lowen, a virologist at Emory University, anticipates that SARS-CoV-2 will continue to show “a clear wintertime seasonality in temperate regions of the world.” Winter is also a time when our bodies can be more susceptible to respiratory bugs: Cold, dry air can interfere with the movement of mucus that shuttles microbes out of the nose and throat; aridity can also make the cells that line those passageways shrivel and die; certain immune defenses might get a bit sleepier, with vitamin D in shorter supply.

    None of that precludes SARS-CoV-2 spread in the heat, even if experts aren’t sure why the virus so easily drives summer waves. Plenty of other microbes manage it: enteroviruses, polio, and more. Even rhinoviruses and adenoviruses, two of the most frequent causes of colds, tend to spread year-round, sometimes showing up in force during the year’s hottest months. (Many scientists presume that has something to do with these viruses’ relatively hardy outer layer, but the reason is undoubtedly more complex than that.) An oft-touted explanation for COVID’s summer waves is that people in certain parts of the country retreat indoors to beat the heat. But that argument alone “is weak,” Lowen told me. In industrialized nations, people spend more than 90 percent of their time indoors.

    That said, an accumulation of many small influences can together create a seasonal tipping point. Summer is a particularly popular time for travel, often to big gatherings. Many months out from winter and its numerous infections and vaccinations, population immunity might also be at a relative low at this time of year, Rivers said. Plus, for all its similarities to the flu, SARS-CoV-2 is its own beast: It has so far affected people more chronically and more severely, and has generated population-sweeping variants at a far faster pace. Those dynamics can all affect when waves manifest.

    And although certain bodily defenses do dip in the cold, data don’t support the idea that immunity is unilaterally stronger in the summer. Micaela Martinez, the director of environmental health at WE ACT for Environmental Justice, in New York, told me the situation is far more complicated than that. For years, she and other researchers have been gathering evidence that suggests that our bodies have distinctly seasonal immunological profiles—with some defensive molecules spiking in the summer and another set in winter. The consequences of those shifts aren’t yet apparent. But some of them could help explain when the coronavirus spreads. By the same token, winter is not a time of disease-ridden doom. Xaquin Castro Dopico, an immunologist at the Karolinska Institute, in Sweden, has found that immune systems in the Northern Hemisphere might be more inflammation-prone in the winter—which, yes, could make certain bouts of illness more severe but could also improve responses to certain vaccinations.

    All of those explanations could apply to COVID’s summer swings—or perhaps none does. “Everybody always wants to have a very simple seasonal answer,” Martinez told me. But one may simply not exist. Even the reasons for the seasonality of polio, a staunch summertime disease prior to its elimination in the U.S., have been “an open question” for many decades, Martinez told me.

    Rivers is hopeful that the coronavirus’s permanent patterns may already be starting to peek through: a wintry heyday, and a smaller maybe-summer hump. “We’re in year four, and we’re seeing the same thing year over year,” she told me. But some experts worry that discussions of COVID-19 seasonality are premature. SARS-CoV-2 is still so fresh to the human population that its patterns could be far from their final form. At an extreme, the patterns researchers observed during the first few years of the pandemic may not prelude the future much at all, because they encapsulate so much change: the initial lack and rapid acquisition of immunity, the virus’s evolution, the ebb and flow of masks, and more. Amid that mishmash of countervailing influences, says Brandon Ogbunu, an infectious-disease modeler at Yale, “you’re going to get some counterintuitive dynamics” that won’t necessarily last long term.

    Read: The next stage of COVID is starting now

    With so much of the world now infected, vaccinated, or both, and COVID mitigations almost entirely gone, the global situation is less in flux now. The virus itself, although still clearly changing at a blistering pace, has not pulled off an Omicron-caliber jump in evolution for more than a year and a half. But no one can yet promise predictability. The cadence of vaccination isn’t yet settled; Scarpino, of Northeastern University, also isn’t ready to dismiss the idea of a viral evolution surprise. Maybe summer waves, to the extent that they’re happening, are a sign that SARS-CoV-2 will remain a microbe for all seasons. Or maybe they’re part of the pandemic’s death rattle—noise in a system that hasn’t yet quieted down.

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    Katherine J. Wu

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  • The COVID Question That Will Take Decades to Answer

    The COVID Question That Will Take Decades to Answer

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    To be a newborn in the year 2023—and, almost certainly, every year that follows—means emerging into a world where the coronavirus is ubiquitous. Babies might not meet the virus in the first week or month of life, but soon enough, SARS-CoV-2 will find them. “For anyone born into this world, it’s not going to take a lot of time for them to become infected,” maybe a year, maybe two, says Katia Koelle, a virologist and infectious-disease modeler at Emory University. Beyond a shadow of a doubt, this virus will be one of the very first serious pathogens that today’s infants—and all future infants—meet.

    Three years into the coronavirus pandemic, these babies are on the leading edge of a generational turnover that will define the rest of our relationship with SARS-CoV-2. They and their slightly older peers are slated to be the first humans who may still be alive when COVID-19 truly hits a new turning point: when almost everyone on Earth has acquired a degree of immunity to the virus as a very young child.

    Read: Is COVID a common cold yet?

    That future crossroads might not sound all that different from where the world is currently. With vaccines now common in most countries and the virus so transmissible, a significant majority of people have some degree of immunity. And in recent months, the world has begun to witness the consequences of that shift. The flux of COVID cases and hospitalizations in most countries seems to be stabilizing into a seasonal-ish sine wave; disease has gotten, on average, less severe, and long COVID seems to be somewhat less likely among those who have recently gotten shots. Even the virus’s evolution seems to be plodding, making minor tweaks to its genetic code, rather than major changes that require another Greek-letter name.

    But today’s status quo may be more of a layover than a final destination in our journey toward COVID’s final form. Against SARS-CoV-2, most little kids have fared reasonably well. And as more babies have been born into a SARS-CoV-2-ridden world, the average age of first exposure to this coronavirus has been steadily dropping—a trend that could continue to massage COVID-19 into a milder disease. Eventually, the expectation is that the illness will reach a stable nadir, at which point it may truly be “another common cold,” says Rustom Antia, an infectious-disease modeler at Emory.

    The full outcome of this living experiment, though, won’t be clear for decades—well after the billions of people who encountered the coronavirus for the first time in adulthood are long gone. The experiences that today’s youngest children have with the virus are only just beginning to shape what it will mean to have COVID throughout a lifetime, when we all coexist with it from birth to death as a matter of course.

    At the beginning of SARS-CoV-2’s global tear, the coronavirus was eager to infect all of us, and we had no immunity to rebuff its attempts. But vulnerability wasn’t just about immune defenses: Age, too, has turned out to be key to resilience. Much of the horror of the disease could be traced to having not only a large population that lacked protection against the virus—but a large adult population that lacked protection against the virus. Had the entire world been made up of grade-schoolers when the pandemic arrived, “I don’t think it would have been nearly as severe,” says Juliet Pulliam, an infectious-disease modeler at Stellenbosch University, in South Africa.

    Across several viral diseases—polio, chicken pox, mumps, SARS, measles, and more—getting sick as an adult is notably more dangerous than as a kid, a trend that’s typically exacerbated when people don’t have any vaccinations or infections to those pathogens in their rearview. The manageable infections that strike toddlers and grade-schoolers may turn serious when they first manifest at older ages, landing people in the hospital with pneumonia, brain swelling, even blindness, and eventually killing some. When scientists plot mortality data by age, many curves bend into “a pretty striking J shape,” says Dylan Morris, an infectious-disease modeler at UCLA.

    The reason for that age differential isn’t always clear. Some of kids’ resilience probably comes from having a young, spry body, far less likely to be burdened with chronic medical conditions that raise severe disease risk. But the quick-wittedness of the young immune system is also likely playing a role. Several studies have found that children are much better at marshaling hordes of interferon—an immune molecule that armors cells against viruses—and may harbor larger, more efficient cavalries of infected-cell-annihilating T cells. That performance peaks sometime around grade school or middle school, says Janet Chou, a pediatrician at Boston Children’s Hospital. After that, our molecular defenses begin a rapid tumble, growing progressively creakier, clumsier, sluggish, and likelier to launch misguided attacks against the tissues that house them. By the time we’re deep into adulthood, our immune systems are no longer sprightly, or terribly well calibrated. When we get sick, our bodies end up rife with inflammation. And our immune cells, weary and depleted, are far less unable to fight off the pathogens they once so easily trounced.

    Whatever the explanations, children are far less likely to experience serious symptoms, or to end up in the hospital or the ICU after being infected with SARS-CoV-2. Long COVID, too, seems to be less prevalent in younger cohorts, says Alexandra Yonts, a pediatrician at Children’s National Hospital. And although some children still develop MIS-C, a rare and dangerous inflammatory condition that can appear weeks after they catch the virus, the condition “seems to have dissipated” as the pandemic has worn on, says Betsy Herold, the chief of pediatric infectious disease at the Children’s Hospital at Montefiore, in the Bronx.

    Should those patterns hold, and as the age of first exposure continues to fall, COVID is likely to become less intense. The relative mildness of childhood encounters with the virus could mean that almost everyone’s first infection—which tends, on average, to be more severe than the ones that immediately follow—could rank low in intensity, setting a sort of ceiling for subsequent bouts. That might make concentrating first encounters “in the younger age group actually a good thing,” says Ruian Ke, an infectious-disease modeler at Los Alamos National Laboratory.

    COVID will likely remain capable of killing, hospitalizing, and chronically debilitating a subset of adults and kids alike. But the hope, experts told me, is that the proportion of individuals who face the worst outcomes will continue to drop. That may be what happened in the aftermath of the 1918 flu pandemic, Antia, of Emory, told me: That strain of the virus stuck around, but never caused the same devastation again. Some researchers suspect that something similar may have even played out with another human coronavirus, OC43: After sparking a devastating pandemic in the 19th century, it’s possible that the virus no longer managed to wreak much more havoc than a common cold in a population that had almost universally encountered it early in life.

    Such a fate for COVID, though, isn’t a guarantee. The virus’s propensity to linger in the body’s nooks and crannies, sometimes causing symptoms that last many months or years, could make it an outlier among its coronaviral kin, says Melody Zeng, an immunologist at Cornell University. And even if the disease is likely to get better than what it is now, that is not a very high bar to clear.

    Some small subset of the population will always be naive to the virus—and it’s not exactly a comfort that in the future, that cohort will almost exclusively be composed of our kids. Pediatric immune systems are robust, UCLA’s Morris told me. But “robust is not the same as infallible.” Since the start of the pandemic, more than 2,000 Americans under the age of 18 have died from COVID—a small fraction of total deaths, but enough to make the disease a leading cause of death for children in the U.S. MIS-C and long COVID may not be common, but their consequences are no less devastating for the children who experience them. Some risks are especially concentrated among our youngest kids, under the age 5, whose immune defenses are still revving up, making them more vulnerable than their slightly older peers. There’s especially little to safeguard newborns just under six months, who aren’t yet eligible for most vaccines—including COVID shots—and who are rapidly losing the antibody-based protection passed down from their mothers while they were in the womb.

    A younger average age of first infection will also probably increase the total number of exposures people have to SARS-CoV-2 in a typical lifetime—each instance carrying some risk of severe or chronic disease. Ke worries the cumulative toll that this repetition could exact: Studies have shown that each subsequent tussle with the virus has the potential to further erode the functioning or structural integrity of organs throughout the body, raising the chances of chronic damage. There’s no telling how many encounters might push an individual past a healthy tipping point.

    Racking up exposures also won’t always bode well for the later chapters of these children’s lives. Decades from now, nearly everyone will have banked plenty of encounters with SARS-CoV-2 by the time they reach advanced age, Chou, from Boston Children’s Hospital, told me. But the virus will also continue to change its appearance, and occasionally escape the immunity that some people built up as kids. Even absent those evasions, as their immune systems wither, many older people may not be able to leverage past experiences with the disease to much benefit. The American experience with influenza is telling. Despite a lifetime of infections and available vaccines, tens of thousands of people typically die annually of the disease in the United States alone, says Ofer Levy, the director of the Precision Vaccines Program at Boston Children’s Hospital. So even with the expected COVID softening, “I don’t think we’re going to reach a point where it’s, Oh well, tra-la-la,” Levy told me. And the protection that immunity offers can have caveats: Decades of research with influenza suggest that immune systems can get a bit hung up on the first versions of a virus that they see, biasing them against mounting strong attacks against other strains; SARS-CoV-2 now seems to be following that pattern. Depending on the coronavirus variants that kids encounter first, their responses and vulnerability to future bouts of illness may vary, says Scott Hensley, an immunologist at the University of Pennsylvania.

    Read: Are our immune systems stuck in 2020?

    Early vaccinations—that ideally target multiple versions of SARS-CoV-2—could make a big difference in reducing just about every bad outcome the virus threatens. Severe disease, long COVID, and transmission to other children and vulnerable adults all would likely be “reduced, prevented, and avoided,” Chou told me. But that’s only if very young kids are taking those shots, which, right now, isn’t at all the case. Nor are they necessarily getting protection passed down during gestation or early life from their mothers, because many adults are not up to date on COVID shots.

    Some of these issues could, in theory, end up moot. A hundred or so years from now, COVID could simply be another common cold, indistinguishable in practice from any other. But Morris points out that this reality, too, wouldn’t fully spare us. “When we bother to look at the burden of the other human coronaviruses, the ones who have been with us for ages? In the elderly, it’s real,” he told me. One study found that a nursing-home outbreak of OC43—the purported former pandemic coronavirus—carried an 8 percent fatality rate; another, caused by NL63, killed three out of the 20 people who caught it in a long-term-care facility in 2017. These and other “mild” respiratory viruses also continue to pose a threat to people of any age who are immunocompromised.

    SARS-CoV-2 doesn’t need to follow in those footsteps. It’s the only human coronavirus against which we have vaccines—which makes the true best-case scenario one in which it ends up even milder than a common cold, because we proactively protect against it. Disease would not need to be as inevitable; the vaccine, rather than the virus, could be the first bit of intel on the disease that kids receive. Tomorrow’s children probably won’t live in a COVID-free world. But they could at least be spared many of the burdens we’re carrying now.

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    Katherine J. Wu

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  • Will Nasal COVID Vaccines Save Us?

    Will Nasal COVID Vaccines Save Us?

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    Since the early days of the coronavirus pandemic, a niche subset of experimental vaccines has offered the world a tantalizing promise: a sustained slowdown in the spread of disease. Formulated to spritz protection into the body via the nose or the mouth—the same portals of entry most accessible to the virus itself—mucosal vaccines could head SARS-CoV-2 off at the pass, stamping out infection to a degree that their injectable counterparts might never hope to achieve.

    Now, nearly three years into the pandemic, mucosal vaccines are popping up all over the map. In September, India authorized one delivered as drops into the nostrils; around the same time, mainland China green-lit an inhalable immunization, and later on, a nasal-spray vaccine, now both being rolled out amid a massive case wave. Two more mucosal recipes have been quietly bopping around in Russia and Iran for many months. Some of the world’s largest and most populous countries now have access to the technology—and yet it isn’t clear how well that’s working out. “Nothing has been published; no data has been made available,” says Mike Diamond, an immunologist at Washington University in St. Louis, whose own approach to mucosal vaccines has been licensed for use in India via a company called Bharat. If mucosal vaccines are delivering on their promise, we don’t know it yet; we don’t know if they will ever deliver.

    The allure of a mucosal vaccine is all about geography. Injectable shots are great at coaxing out immune defenses in the blood, where they’re able to cut down on the risk of severe disease and death. But they aren’t as good at marshaling a protective response in the upper airway, leaving an opening for the virus to still infect and transmit. When viral invaders throng the nose, blood-borne defenses have to scamper to the site of infection at a bit of a delay—it’s like stationing guards next to a bank’s central vault, only to have them rush to the entrance every time a robber trips an external alarm. Mucosal vaccines, meanwhile, would presumably be working at the door.

    That same logic drives the effectiveness of the powerful oral polio vaccine, which bolsters defenses in its target virus’s preferred environment—the gut. Just one mucosal vaccine exists to combat a pathogen that enters through the nose: a nasal spray made up of weakened flu viruses, a version of which is branded as FluMist. The up-the-nose spritz is reasonably protective in kids, in some cases even outperforming its injected counterparts (though not always). But FluMist is much less potent for adults: The immunity they accumulate from a lifetime of influenza infections can wipe out the vaccine before it has time to lay down new protection. When it comes to cooking up a mucosal vaccine for a respiratory virus, “we don’t have a great template to follow,” says Deepta Bhattacharya, an immunologist at the University of Arizona.

    To circumvent the FluMist problem, some researchers have instead concocted viral-vector-based vaccines—the same group of immunizations to which the Johnson & Johnson and AstraZeneca COVID shots belong. China’s two mucosal vaccines fall into this category; so does India’s nose-drop concoction, as well as a nasal version of Russia’s Sputnik V shot. Other researchers are cooking up vaccines that contain ready-made molecules of the coronavirus’s spike protein, more akin to the shot from Novavax. Among them are Iran’s mucosal COVID vaccine and a newer, still-in-development candidate from the immunologist Akiko Iwasaki and her colleagues at Yale. The Yale group is also testing an mRNA-based nasal recipe. And the company Vaxart has been tinkering with a COVID-vaccine pill that could be swallowed to provoke immune cells in the gut, which would then deploy fighters throughout the body’s mucosal surfaces, up through the nose.

    Early data in animals have spurred some optimism. Trial versions of Diamond’s vaccine guarded mice, hamsters, and monkeys from the virus, in some cases seeming to stave off infection entirely; a miniaturized version of Vaxart’s oral vaccine was able to keep infected hamsters from spreading the coronavirus through the air. Iwasaki is pursuing an approach that deploys mucosal vaccines exclusively as boosters to injected shots, in the hopes that the initial jab can lay down bodywide immunity, a subset of which can then be tugged into a specialized compartment in the nose. Her nasal-protein recipe seems to trim transmission rates among rodents that have first received an in-the-muscle shot.

    But attempts to re-create these results in people yielded mixed results. After an intranasal version of the AstraZeneca vaccine roused great defenses in animals, a team at Oxford moved the immunization into a small human trial—and last month, published results showing that it hardly triggered any immune response, even as a booster to an in-the-arm shot. Adam Ritchie, one of the Oxford immunologists behind the study, told me the results don’t necessarily spell disaster for other mucosal attempts, and that with more finagling, AstraZeneca’s vaccine might someday do better up the nose. Still, the results “definitely put a damper on the excitement around intranasal vaccines,” says Stephanie Langel, an immunologist at Case Western Reserve University, who’s partnering with Vaxart to develop a COVID-vaccine pill.

    The mucosal COVID vaccines in India and China, at least, have reportedly shown a bit more promise in small, early human trials. Bharat’s info sheet on its nasal-drop vaccine—the Indian riff on Diamond’s recipe—says it bested another locally made vaccine, Covaxin, at tickling out antibodies, while provoking fewer side effects. China’s inhaled vaccine, too, seems to do reasonably well on the human-antibody front. But antibodies aren’t the same as true effectiveness: Vaccine makers and local health ministries, experts told me, have yet to release large-scale, real-world data showing that the vaccines substantially cut down on transmission or infection. And although some studies have hinted that nasal protection can stick around in animals for many, many months, there’s no guarantee the same will be true in humans, in whom mucosal antibodies, in particular, “are kind of known to wane pretty quickly,” Langel told me.

    SARS-CoV-2 infections have offered sobering lessons of their own. The nasal immune response to the virus itself is neither impenetrable nor particularly long-lived, says David Martinez, a viral immunologist at the University of North Carolina at Chapel Hill. Even people who have been both vaccinated and infected can still get infected again, he told me, and it would be difficult for a nasal vaccine to do much better. “I don’t think mucosal vaccines are going to be the deus ex machina that some people think they’re going to be.”

    Read: America’s flu-shot problem is also its next COVID-shot problem

    Mucosal vaccines don’t need to provide a perfect blockade against infection to prove valuable. Packaged into sprays, drops, or pills, immunizations tailor-made for the mouth or the nose might make COVID vaccines easier to ship, store, and distribute en masse. “They often don’t require specialized training,” says Gregory Poland, a vaccinologist at the Mayo Clinic—a major advantage for rural or low-resource areas. The immunizing experience could also be easier for kids or anyone else who’d rather not endure a needle. Should something like Vaxart’s encapsulated vaccine work out, Langel told me, COVID vaccines could even one day be shipped via mail, in a form safe and easy enough to swallow with a glass of water at home. Some formulations may also come with far fewer side effects than, say, the mRNA-based shots, which “really kick my ass,” Bhattacharya told me. Even if mucosal vaccines weren’t a transmission-blocking knockout, “if it meant I didn’t have to get the mRNA vaccine, I would consider it.”

    But the longer that countries such as the U.S. have gone without mucosal COVID vaccines, the harder it’s gotten to get one across the finish line. Transmission, in particular, is tough to study, and Langel pointed out that any new immunizations will likely have to prove that they can outperform our current crop of injected shots to secure funding, possibly even FDA approval. “It’s an uphill battle,” she told me.

    Top White House advisers remain resolute that transmission-reducing tech has to be part of the next generation of COVID vaccines. Ideally, those advancements would be paired with ingredients that enhance the life span of immune responses and combat a wider swath of variants; skimp on any of them, and the U.S. might remain in repeat-vaccination purgatory for a while yet. “We need to do better on all three fronts,” Anthony Fauci, the outgoing director of the National Institute of Allergy and Infectious Diseases, told me. But packaging all that together will require another major financial investment. “We need Warp Speed 2.0,” says Shankar Musunuri, the CEO of Ocugen, the American company that has licensed Diamond’s recipe. “And so far, there is no action.” When I asked Fauci about this, he didn’t seem optimistic that this would change. “I think that they’ve reached the point where they feel, ‘We’ve given enough money to it,’” he told me. In the absence of dedicated government funds, some scientists, Iwasaki among them, have decided to spin off companies of their own. But without more public urgency and cash flow, “it could be years to decades to market,” Iwasaki told me. “And that’s if everything goes well.”

    Read: The three COVID developments I’m still holding out hope for

    Then there’s the issue of uptake. Musunuri told me that he’s confident that the introduction of mucosal COVID vaccines in the U.S.—however long it takes to happen—will “attract all populations, including kids … people like new things.” But Rupali Limaye, a behavioral scientist at Johns Hopkins University, worries that for some, novelty will drive the exact opposite effect. The “newness” of COVID vaccines, she told me, is exactly what has prompted many to adopt an attitude of “wait and see” or even “that’s not for me.” An even newer one that jets ingredients up into the head might be met with additional reproach.

    Vaccine fatigue has also set in for much of the public. In the United States, hospitalizations are once again rising, and yet less than 15 percent of people eligible for bivalent shots have gotten them. That sort of uptake is at odds with the dream of a mucosal vaccine that can drive down transmission. “It would have to be a lot of people getting vaccinated in order to have that public-health population impact,” says Ben Cowling, an epidemiologist at the University of Hong Kong. And there’s no guarantee that even a widely administered mucosal vaccine would be the population’s final dose. The pace at which we’re doling out shots is driven in part by “the virus changing so quickly,” says Ali Ellebedy, an immunologist at Washington University in St. Louis. Even a sustained encampment of antibodies in the nose could end up being a poor match for the next variant that comes along, necessitating yet another update.

    The experts I spoke with worried that some members of the scientific community—even some members of the public—have begun to pin all their hopes about stopping the spread of SARS-CoV-2 on mucosal vaccines. It’s a recipe for disappointment. “People love the idea of a magic pill,” Langel told me. “But it’s just not reality.” The virus is here to stay; the goal continues to be to make that reality more survivable. “We’re trying to reduce infection and transmission, not eliminate it; that would be almost impossible,” Iwasaki told me. That’s true for any vaccine, no matter how, or where, the body first encounters it.

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    Katherine J. Wu

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