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  • The Future of Long COVID

    The Future of Long COVID

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    In the early spring of 2020, the condition we now call long COVID didn’t have a name, much less a large community of patient advocates. For the most part, clinicians dismissed its symptoms, and researchers focused on SARS-CoV-2 infections’ short-term effects. Now, as the pandemic approaches the end of its third winter in the Northern Hemisphere, the chronic toll of the coronavirus is much more familiar. Long COVID has been acknowledged by prominent experts, national leaders, and the World Health Organization; the National Institutes of Health has set up a billion-dollar research program to understand how and in whom its symptoms unfurl. Hundreds of long-COVID clinics now freckle the American landscape, offering services in nearly every state; and recent data hint that well-vetted drugs to treat or prevent long COVID may someday be widespread. Long COVID and the people battling it are commanding more respect, says Hannah Davis, a co-founder of the Patient-Led Research Collaborative, who has had long COVID for nearly three years: Finally, many people “seem willing to understand.”

    But for all the ground that’s been gained, the road ahead is arduous. Long COVID still lacks a universal clinical definition and a standard diagnosis protocol; there’s no consensus on its prevalence, or even what symptoms fall under its purview. Although experts now agree that long COVID does not refer to a single illness, but rather is an umbrella term, like cancer, they disagree on the number of subtypes that fall within it and how, exactly, each might manifest. Some risk factors—among them, a COVID hospitalization, female sex, and certain preexisting medical conditions—have been identified, but researchers are still trying to identify others amid fluctuating population immunity and the endless slog of viral variants. And for people who have long COVID now, or might develop it soon, the interventions are still scant. To this day, “when someone asks me, ‘How can I not get long COVID?’ I can still only say, ‘Don’t get COVID,’” says David Putrino, a neuroscientist and physical therapist who leads a long-COVID rehabilitation clinic at Mount Sinai’s Icahn School of Medicine.

    As the world turns its gaze away from the coronavirus pandemic, with country after country declaring the virus “endemic” and allowing crisis-caliber interventions to lapse, long-COVID researchers, patients, and activists worry that even past progress could be undone. The momentum of the past three years now feels bittersweet, they told me, in that it represents what the community might lose. Experts can’t yet say whether the number of long-haulers will continue to increase, or offer a definitive prognosis for those who have been battling the condition for months or years. All that’s clear right now is that, despite America’s current stance on the coronavirus, long COVID is far from being beaten.


    Despite an influx of resources into long-COVID research in recent months, data on the condition’s current reach remain a mess—and scientists still can’t fully quantify its risks.

    Recent evidence from two long-term surveys have hinted that the pool of long-haulers might be shrinking, even as new infection rates remain sky-high: Earlier this month, the United Kingdom’s Office for National Statistics released data showing that 2 million people self-reported lingering symptoms at the very start of 2023, down from 2.3 million in August 2022. The U.S. CDC’s Household Pulse Survey, another study based on self-reporting, also recorded a small drop in long-COVID prevalence in the same time frame, from about 7.5 percent of all American adults to roughly 6. Against the massive number of infections that have continued to slam both countries in the pandemic’s third year and beyond, these surveys might seem to imply that long-haulers are leaving the pool faster than newcomers are arriving.

    Experts cautioned, however, that there are plenty of reasons to treat these patterns carefully—and to not assume that the trends will be sustained. It’s certainly better that these data aren’t showing a sustained, dramatic uptick in long-COVID cases. But that doesn’t mean the situation is improving. Throughout the pandemic, the size of the long-COVID pool has contracted or expanded for only two reasons: a change in the rate at which people enter, or at which they exit. Both figures are likely to be in constant flux, as surges of infections come and go, masking habits change, and vaccine and antiviral uptake fluctuates. Davis pointed out that the slight downward tick in both studies captured just a half-year stretch, so the downward slope could be one small portion of an undulating wave. A few hours spent at the beach while the tide is going out wouldn’t be enough to prove that the ocean is drying up.

    Recent counts of new long-COVID cases might also be undercounts, as testing slows and people encounter more challenges getting diagnosed. That said, it’s still possible that, on a case-by-case basis, the likelihood of any individual developing long COVID after a SARS-CoV-2 infection may have fallen since the pandemic’s start, says Deepti Gurdasani, a clinical epidemiologist at Queen Mary University of London and the University of New South Wales. Population immunity—especially acquired via vaccination—has, over the past three years, better steeled people’s bodies against the virus, and strong evidence supports the notion that vaccines can moderately reduce the risk of developing long COVID. Treatments and behavioral interventions that have become more commonplace may have chipped away at incidence as well. Antivirals can now help to corral the virus early in infection; ventilation, distancing, and masks—when they’re used—can trim the amount of virus that infiltrates the body. And if overall exposure to the virus can influence the likelihood of developing long COVID, that could help explain why so many debilitating cases arose at the very start of the pandemic, when interventions were few and far between, says Steven Deeks, a physician researcher at UC San Francisco.

    There’s not much comfort to derive from those individual-level stats, though, when considering what’s happening on broader scales. Even if immunity makes the average infected person less likely to fall into the long-COVID pool, so many people have been catching the virus that the inbound rate still feels like a flood. “The level of infection in many countries has gone up substantially since 2021,” Gurdasani told me. The majority of long-COVID cases arise after mild infections, the sort for which our immune defenses fade most rapidly. Now that masking and physical distancing have fallen by the wayside, people may be getting exposed to higher viral doses than they were a year or two ago. In absolute terms, then, the number of people entering the long-COVID pool may not really be decreasing. Even if the pool were getting slightly smaller, its size would still be staggering, an ocean of patients with titanic needs. “Anecdotally, we still have an enormous waitlist to get into our clinic,” Putrino told me.

    Deeks told me that he’s seen another possible reason for optimism: People with newer cases of long COVID might be experiencing less debilitating or faster-improving disease, based on what he’s seen. “The worst cases we’ve seen come from the first wave in 2020,” he said. But Putrino isn’t so sure. “If you put an Omicron long-COVID patient in front of me, versus one from the first wave, I wouldn’t be able to tell you who was who,” he said. The two cases would also be difficult to compare, because they’re separated by so much time. Long COVID’s symptoms can wax, wane, and qualitatively change; a couple of years into the future, some long-haulers who’ve just developed the condition may be in a spot that’s similar to where many veterans with the condition are now.

    Experts’ understanding of how often people depart the long-COVID pool is also meager. Some long-haulers have undoubtedly seen improvement—but without clear lines distinguishing short COVID from medium and long COVID, entry and exit into these various groups is easy to over- or underestimate. What few data exist on the likelihood of recovery or remission is inconsistent, and not always rosy: Investigators of RECOVER, a large national study of long COVID, have calculated that about two-thirds of the long-haulers in their cohort do not return to baseline health. Putrino, who has worked with hundreds of long-haulers since the pandemic began, estimates that although most of his patients experience at least some benefit from a few months of rehabilitation, only about one-fifth to one-quarter of them eventually reach the point of feeling about as well as they did before catching the virus, while the majority hit a middling plateau. A small minority of the people he has treated, he told me, never seem to improve at all.

    Letícia Soares, a long-hauler in Brazil who caught the virus near the start of the pandemic, falls into that final category. Once a disease ecologist who studied parasite transmission in birds, she is now mostly housebound, working when she is able as a researcher for the Patient-Led Research Collaborative. Her days revolve around medications and behavioral modifications she uses for her fatigue, sleeplessness, and chronic pain. Soares no longer has the capacity to cook or frequently venture outside. And she has resigned herself to this status quo until the treatment landscape changes drastically. It is not the life she pictured for herself, Soares told me. “Sometimes I think the person I used to be died in April of 2020.”

    Even long-haulers who have noticed an improvement in their symptoms are wary of overconfidence. Some absolutely do experience what could be called recovery—but for others, the term has gotten loaded, almost a jinx. “If the question is, ‘Are you doing the things you were doing in 2019?’ the answer is largely no,” says JD Davids, a chronic-illness advocate based in New York. For some, he told me, “getting better” has been more defined by a resetting of expectations than a return to good health. Relapses are also not uncommon, especially after repeat encounters with the virus. Lisa McCorkell, a long-hauler and a co-founder of the Patient-Led Research Collaborative, has felt her symptoms partly abate since she first fell ill in the spring of 2020. But, she told me, she suspects that her condition is more likely to deteriorate than further improve—partly because of “how easy it is to get reinfected now.”


    Last week, in his State of the Union address, President Joe Biden told the American public that “we have broken COVID’s grip on us.” Highlighting the declines in the rates of COVID deaths, the millions of lives saved, and the importance of remembering the more than 1 million lost, Biden reminded the nation of what was to come: “Soon we’ll end the public-health emergency.”

    When the U.S.’s state of emergency was declared nearly three years ago, as hospitals were overrun and morgues overflowed, the focus was on severe, short-term disease. Perhaps in that sense, the emergency is close to being over, Deeks told me. But long COVID, though slower to command attention, has since become its own emergency, never formally declared; for the millions of Americans who have been affected by the condition, their relationship with the virus does not yet seem to be in a better place.

    Even with many more health-care providers clued into long COVID’s ills, the waiting lists for rehabilitation and treatment remain untenable, Hannah Davis told me. “I consider myself someone who gets exceptional care compared to other people,” she said. “And still, I hear from my doctor every nine or 10 months.” Calling a wrap on COVID’s “emergency” phase could worsen that already skewed supply-demand ratio. Changes to the nation’s funding tactics could strip resources—among them, access to telehealth; Medicaid coverage; and affordable antivirals, tests, and vaccines—from vulnerable populations, including people of color, that aren’t getting their needs met even as things stand, McCorkell told me. And as clinicians internalize the message that the coronavirus has largely been addressed, attention to its chronic impacts may dwindle. At least one of the country’s long-COVID clinics has, in recent months, announced plans to close, and Davis worries that more could follow soon.

    Scientists researching long COVID are also expecting new challenges. Reduced access to testing will complicate efforts to figure out how many people are developing the condition, and who’s most at risk. Should researchers turn their scientific focus away from studying causes and cures for long COVID when the emergency declaration lifts, Davids and others worry that there will be ripple effects on the scientific community’s interest in other, neglected chronic illnesses, such as ME/CFS (myalgic encephalomyelitis or chronic fatigue syndrome), a diagnosis that many long-haulers have also received.

    The end of the U.S.’s official crisis mode on COVID could stymie research in other ways as well. At Johns Hopkins University, the infectious-disease epidemiologists Priya Duggal, Shruti Mehta, and Bryan Lau have been running a large study to better understand the conditions and circumstances that lead to long COVID, and how symptoms evolve over time. In the past two years, they have gathered online survey data from thousands of people who both have and haven’t been infected, and who have and haven’t seen their symptoms rapidly resolve. But as of late, they’ve been struggling to recruit enough people who caught the virus and didn’t feel their symptoms linger. “I think that the people who are suffering from long COVID will always do their best to participate,” Duggal told me. That may not be the case for individuals whose experiences with the virus were brief. A lot of them “are completely over it,” Duggal said. “Their life has moved on.”

    Kate Porter, a Massachusetts-based marketing director, told me that she worries about her family’s future, should long COVID fade from the national discourse. She and her teenage daughter both caught the virus in the spring of 2020, and went on to develop chronic symptoms; their experience with the disease isn’t yet over. “Just because the emergency declaration is expiring, that doesn’t mean that suddenly people are magically going to get better and this issue is going to go away,” Porter told me. After months of relative improvement, her daughter is now fighting prolonged bouts of fatigue that are affecting her school life—and Porter isn’t sure how receptive people will be to her explanations, should their illnesses persist for years to come. “Two years from now, how am I going to explain, ‘Well, this is from COVID, five years ago’?” she said.

    A condition that was once mired in skepticism, scorn, and gaslighting, long COVID now has recognition—but empathy for long-haulers could yet experience a backslide. Nisreen Alwan, a public-health researcher at the University of Southampton, in the U.K., and her colleagues have found that many long-haulers still worry about disclosing their condition, fearing that it could jeopardize their employment, social interactions, and more. Long COVID could soon be slated to become just one of many neglected chronic diseases, poorly understood and rarely discussed.

    Davis doesn’t think that marginalization is inevitable. Her reasoning is grim: Other chronic illnesses have been easier to push to the sidelines, she said, on account of their smaller clinical footprint, but the pool of long-haulers is enormous—comprising millions of people in the U.S. alone. “I think it’s going to be impossible to ignore,” she told me. One way or another, the world will have no choice but to look.

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    Katherine J. Wu

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  • I’m Sorry, but This COVID Policy Is Ridiculous

    I’m Sorry, but This COVID Policy Is Ridiculous

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    Cases have surged in China since it dropped its zero-COVID policy in December, and the latest models now suggest that at least 1 million people may die as a result. Many countries have responded by policing their borders: Last week, the CDC announced that anyone entering the United States from China would be required to test negative within two days of departure; the U.K., Canada, and Australia quickly followed suit; and the European Union has urged its member states to do the same. (Taking a more extreme tack, Morocco has said it will ban travelers from China from entering altogether.) At a media briefing on Wednesday, World Health Organization Director-General Tedros Adhanom Ghebreyesus said, “It is understandable that some countries are taking steps they believe will protect their own citizens.”

    On Tuesday, a Chinese official denounced some of the new restrictions as having “no scientific basis.” She wasn’t wrong. If the goal is to “slow the spread of COVID” from overseas, as the CDC has stated, there is little evidence to suggest that the restrictions will be effective. More important, it wouldn’t matter if they were: COVID is already spreading unchecked in the U.S. and many of the other countries that have new rules in place, so imported cases wouldn’t make much of a difference. The risk is particularly low given the fact that 95 percent of China’s locally acquired cases are being caused by two Omicron lineages—BA.5.2 and BF.7—that are old news elsewhere. “The most dangerous new variant at the moment is from New York—XBB.1.5—which the U.S. is now busy exporting to the rest of the world,” Christina Pagel, a mathematician who studies health care at University College London, told me. “I’m sorry, but this is fucking ridiculous.”

    By now, it’s well known that travel restrictions can’t stop COVID from crossing borders. At best, they slow its entry. When Omicron was first detected, in South Africa in late November 2021, America blocked travel from southern-African countries in an attempt to prevent the variant from spreading; by mid-December, Omicron dominated the United States. Restrictions can delay the spread of a variant only if they are implemented while cases are low and before travelers have had a chance to spread it. Such policies were more effective early in the pandemic: A BMJ Global Health review concluded that the initial ban on all travel into or out of Wuhan, China, in January 2020 significantly reduced the number of cases exported to other countries and delayed outbreaks elsewhere by “up to a few weeks.” Later on, such restrictions lost value. The COVID Border Accountability Project, which tracks travel restrictions around the world, has found that border closures did not reduce COVID spread, at least through April 2021, Mary Shiraef, the project’s principal investigator and a political scientist at Notre Dame University, told me. (According to the study, domestic lockdowns did slow transmission.)

    At this stage of the pandemic, restrictions make sense only under two conditions, Pagel said: The country deploying them must have low levels of spread and good control policies, and the restrictions must be applied to all other nations, as opposed to just one. Neither of these conditions is being met right now by any country deploying travel measures against China. Even if a single-point ban did serve some useful purpose, the rules in place for China don’t add up. Predeparture testing likely won’t catch most infected travelers from China, Adam Kucharski, a professor of infectious-disease epidemiology at the London School of Hygiene and Tropical Medicine, told me. A person could test negative one day and then positive a few days later. If the point of restrictions is to slow local transmission, Kucharski said, calculations based on his research suggest that travelers should be tested twice: once before they arrive, then about three or four days afterward. Doing so would catch infected travelers who initially tested negative while limiting their window for spreading disease.

    The best possible outcome of a travel restriction like the one the U.S. now has in place would be a very small delay before the arrival of a catastrophic new variant that has just emerged in China. In that scenario, any extra time might be used to intensify mitigation strategies and assess the degree to which current vaccines are expected to hold up. Historically, though, the time saved by travel bans has been wasted. After countries restricted travel from South Africa to keep Omicron at bay, governments responded by “not really doing much at all domestically,” Kucharski said. In any case, as my colleague Katherine J. Wu has pointed out, the virus is able to spread easily in China right now without any further changes to its genome. Population immunity there is modest, owing to the country’s low natural-infection rate and less effective vaccines, so the virus can infect people perfectly well as is.

    The travel restrictions on China will have little impact on the spread of COVID, but they do send a forceful political message. The U.S. measures are meant to pressure China, by slowing its economic rebound, into being transparent about its COVID situation, Stephen Morrison, the director of the Global Health Policy Center at the Center for Strategic and International Studies, a Washington, D.C.-based think tank, told me. China’s alleged official death count, for example—5,259 as of January 4—seems way too low to be believable, especially amid reports of overflowing Chinese hospitals and funeral homes. So long as the country isn’t more forthcoming, Morrison said, then Chinese tourists, who have only recently been allowed to travel internationally, will continue to be unwelcome.

    Expressing this message through a largely pointless public-health measure comes with a price. When that measure fails to keep COVID spread at bay, faith in public-health institutions could decline, which Pagel said is the “biggest danger” for the next pandemic. It also stokes the long-standing fear that Chinese people are more likely to carry disease than anyone else, whether foreign or American. “We are watching this policy so carefully to see if it will once again invite a racial backlash,” Manjusha Kulkarni, a co-founder of Stop AAPI Hate, told me. If a rise in anti-Asian hate and violence comes along with more transparency from China about its COVID situation, the cost of these restrictions hardly seems worth their benefits.

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    Yasmin Tayag

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  • Polio Is Exploiting a Very Human Weakness

    Polio Is Exploiting a Very Human Weakness

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    In 1988, the World Health Assembly announced a very ambitious goal: Polio was to be vanquished by the year 2000. It was a reach, sure, but feasible. Although highly infectious, polioviruses affect only people, and don’t hide out in wild animals; with two extraordinarily effective vaccines in regular use, they should be possible to snuff out. Thanks to a global inoculation campaign, infections had, for years, been going down, down, down.

    But 2000 came and went, as did a second deadline, in 2005, and a third, in 2012, and so on. The world will almost certainly miss an upcoming target at the end of 2023 too. In theory, eradication is still in sight: The virus remains endemic in just two countries—Pakistan and Afghanistan—and two of the three types of wild poliovirus that once troubled humanity are gone. And yet, polio cases are creeping up in several countries that had eliminated them, including the United Kingdom, Israel, and the United States. Earlier this year, New York detected America’s first paralytic polio case in nearly a decade; last week, the governor declared a state of emergency over a fast-ballooning outbreak.

    This is the cruel logic of viruses: Give them enough time—leave enough hosts for them to infect—and they will eventually find a way to spread again. “You have to stop transmission everywhere, all at the same time,” says Kimberly Thompson, a health economist and the president of the nonprofit Kid Risk. Which means eradication will demand a near-perfect syncing of vaccine supply, access, equity, political will, public enthusiasm, and more. To beat the virus, population immunity must outlast it.

    Right now, though, the world’s immunological shield is too porous to stop polio’s spread. At the center of the new epidemics are vaccine-derived polioviruses that have begun to paralyze unimmunized people in places where immunity is low—a snag in the eradication campaign that also happens to be tightly linked to one of its most essential tools. Vaccine performance has always depended on both technology and human behavior. But in this case especially, because of the nature of the foe at hand, those twin pillars must line up as precisely as possible or risk a further backslide into a dangerous past.


    In the grand plan for eradication, our two primary polio vaccines were always meant to complement each other. One, an ultra-effective oral formulation, is powerful and long-lasting enough to quash wild-poliovirus transmission—the perfect “workhorse” for a global vaccination campaign, says Adam Lauring, an evolutionary virologist at the University of Michigan. The other, a supersafe injectable, sweeps in after its colleague has halted outbreaks one country at a time, maintaining a high level of immunity in post-elimination nations while the rest of the world catches up.

    For decades, the shot, chaser approach found remarkable success. In the 1980s, wild poliovirus struck an estimated 300,000 to 400,000 people each year; by 2021, the numbers had plummeted to single digits. But recently, as vaccine coverage in various countries has stalled or slipped, the loopholes in this vaccination tactic have begun to show themselves and grow.

    The oral polio vaccine (OPV), delivered as drops in the mouth, is one of the most effective inoculations in the world’s roster. It contains weakened forms of polioviruses that have been altered away from their paralysis-causing forms but still mimic a wild infection so well that they can stop people from spreading wild pathogens for years, even decades. In the weeks after people receive the vaccine, they can also pass the weakened virus to others in the community, helping protect them too. And OPV’s transportability, low price point, and ease of administration make it a “gold standard for outbreak interruption,” says Ananda Bandyopadhyay, the deputy director for the polio team at the Bill & Melinda Gates Foundation. Since its mid-20th-century debut, OPV has helped dozens of countries—including the U.S.—eliminate the virus. Those nations were then able to phase out OPV and switch to inoculating people with the injected vaccine.

    But OPV’s most potent superpower is also its greatest weakness. Given enough time and opportunity to spread and reproduce, the neutered virus within the vaccine can regain the ability to invade the nervous system and cause paralysis in unvaccinated or immunocompromised people (or in very, very rare cases, the vaccine recipient themselves). Just a small handful of genetic modifications—three or fewer—can spark a reversion, and the mutants, which are “better at replicating” than their kin, can take over fast, says Raul Andino, a virologist at UC San Francisco. In recent years, a few thousand cases of vaccine-derived polio have been detected around the world, far outstripping the toll of wild viruses; dozens of countries, the U.S. now among them, are battling such outbreaks, and the numbers seem to be only going up. Vaccine-derived polio is still a true rarity: Billions of oral vaccines have been delivered since the global campaign began. But it underscores “the real problem” with OPV, Lauring told me. “You’re fighting fire with fire.”

    The injected polio vaccine, or IPV, which contains only chemically inactivated versions of the virus, carries none of that risk. To purge all polio cases, “you have to stop using oral polio vaccine,” Thompson told me, and transition the entire globe to IPV. (Post-eradication, countries would need to keep IPV in their routine immunization schedule for at least 10 years, experts have said.) But the injected vaccine has a different drawback. Although the shot can very effectively stave off paralysis, IPV doesn’t elicit the kind of immunity that stops people from getting infected with polioviruses and then passing them on. In places that rely on injected vaccines, “even immune individuals can participate in transmission,” Thompson told me. Which opens up a vulnerability when too many people have skipped both types of vaccines: Paralyzing polioviruses erupt out of communities where the oral vaccine is still in use—then can spread in undervaccinated areas. It might be tempting to blame OPV for our troubles. But that’s not the main threat, Bandyopadhyay told me. “It’s the lack of adequate vaccination.”

    As things stand, the goal in the endemic countries of Pakistan and Afghanistan remains achieving sufficiently high vaccine coverage, Bandyopadhyay said. But many of the communities in these nations are rural or nomadic, and tough to reach even with convenient drop-in-the-mouth vaccines. Civil and political unrest, misinformation, natural disasters, and most recently, the COVID pandemic have raised additional hurdles. So have intermittent bans on house-to-house vaccination in Afghanistan, says John Vertefeuille, the chief of the polio-eradication branch at the CDC. Cases of wild polio have experienced a recent jump in Pakistan, and have also been imported into the non-endemic countries of Malawi and Mozambique.

    But the toll of those outbreaks—all featuring type 1 polio—currently pales in comparison with those featuring vaccine-derived type 2. The last case of wild type 2 polio was detected in 1999, but that version of the virus has persisted in its modified form in oral polio vaccines. And when it reverts to its dangerous form, it gains particularly infectious oomph, allowing it to spread unchecked wherever immunity is low. Some 30 countries around the world are battling outbreaks of poliovirus whose origin can be traced back to the oral inoculations; vaccine-derived type 2 is what’s been circulating in Jerusalem, London, and New York, where it ultimately paralyzed an unvaccinated young man. The extent to which the virus is churning in other parts of the country isn’t fully known; routine immunization has dropped since the COVID pandemic’s start, and the U.S. hasn’t regularly surveyed its wastewater for the pathogen.

    The success of these vaccine-derived viruses is largely the result of our own hubris—of a failure, experts told me, to sync the world’s efforts. In 2016, 17 years after the last wild type-2 case had been seen, officials decided to pivot to a new version of OPV that would protect against just types 1 and 3, a sort of trial run for the eventual obsolescence of OPV. But the move may have been premature. The switch wasn’t coordinated enough; in too many pockets of the world, type-2 polio, from the three-part oral vaccine, was still moseying about. The result was disastrous. “We opened up an immunity gap,” Thompson told me. Into it, fast-mutating vaccine-derived type-2 viruses spilled, surging onto a global landscape populated with growing numbers of children who lacked protection against it.


    A new oral vaccine, listed for emergency use by the WHO in 2020, could help get the global campaign back on track. The fresh formulation, developed in part by Andino and his colleagues, still relies on the immunity-boosting powers of weakened, replicating polioviruses. But the pathogens within have had their genetic blueprints further tweaked. “We mucked around” with the structure of poliovirus, Andino told me, and figured out a way to make a modified version of type 2 that’s far stabler. It’s much less likely to mutate away from its domesticated, non-paralyzing state, or swap genes with related viruses that could grant the same gifts.

    Technologically, the new oral vaccine, nicknamed nOPV2, seems to be as close to a slam dunk as immunizations can get. “To me, it’s just super cool,” Lauring told me. “You keep all the good things about OPV but mitigate this evolutionary risk.” In the year and a half since the vaccine’s world premiere, some 450 million doses of nOPV2 have found their way into children in 22 countries—and a whopping zero cases of vaccine-derived paralysis have followed.

    But nOPV2 is “not a silver bullet,” Andino said. The vaccine covers just one of the three poliovirus types, which means it can’t yet fully replace the original oral recipe. (Trials for type-1 and -3 versions are ongoing, and even after those recipes are ready for prime time, researchers will have to confirm that the vaccine still works as expected when the three recipes are mixed.) The vaccine’s precise clinical costs are also still a shade unclear. nOPV2 is a safer oral polio vaccine, but it’s still an oral polio vaccine, chock-full of active viral particles. “You can think of it as more attenuated,” Thompson said. “But I don’t think anybody expects that it won’t have any potential to evolve.” And nOPV2’s existence doesn’t change the fact that the world will still have to undergo a total, coordinated switch to IPV before eradication is won.

    As has been the case with COVID vaccines, and so many others, the primary problem isn’t the technology at all—but how humans have deployed it, or failed to. “Vaccine sitting in a vial, no matter how genetically stable and how effective it is, that’s not going to solve the problem of the outbreaks,” Bandyopadhyay said. “It’s really vaccination and getting to that last child in that last community.”

    If dwindling vaccination trends don’t reverse, even our current vaccination strategies could require a rough reboot. In 2013, health officials in Israel—which had, for years prior, run a successful IPV-only campaign for its children—detected wild type-1 virus, imported from abroad, in the country’s sewage, and decided to roll out another round of oral vaccines to kids under 10. Within a few weeks, nearly 80 percent of the targeted population had gotten a dose. Even “polio-free countries are not polio-risk-free,” Bandyopadhyay told me. The situation in New York is different, in part because type-1 polio causes paralysis more often than type-2 does. But should circumstances grow more dire—should substantial outbreaks start elsewhere in the country, should the nation fail to bring IPV coverage back to properly protective levels—America, too, “may have to consider adding OPV as a supplement,” says Purvi Parikh, an immunologist and a physician at NYU, “especially in rural areas” where emergency injected-vaccine campaigns may be tough. Such an approach would be a pretty extreme move, and a “very big political undertaking,” Thompson said, requiring a pivot back to a vaccine that was phased out of use decades ago. And even then, there’s no guarantee that Americans would take the offered oral drops.

    The CDC, for now, is not eager for such a change. Noting that most people in the U.S. are vaccinated against polio, Katherina Grusich, an agency spokesperson, told me that the CDC has no plans to add OPV or nOPV to the American regimen. “We are a long way from reaching for that,” she said.

    But this week, the U.S. joined the WHO’s list of about 30 nations with circulating vaccine-derived-poliovirus outbreaks. The country could have avoided this unfortunate honor had it kept shot uptake more uniformly high. It’s true, as Grusich pointed out, that more than 90 percent of young American children have received IPV. But they are not distributed evenly, which opens up vulnerabilities for the virus to exploit. Here, the U.S., in a sense, had one job: maintain its polio-free status while the rest of the world joined in. That it did not is an admonition, and a reminder of how unmerciful the virus can be. Polio, a fast mutator, preys on human negligence; the vaccines that guard against it contain both a form of protection and a catch that reinforces how risky treating these tools as a discretionary measure can be.

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    Katherine J. Wu

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