Some ten thousand diseases afflict humankind, and we have the power to vanquish only a handful of them. It’s especially tragic, then, when we squander what opportunities we have, whether by choice, neglect, or incompetence. In June, an unvaccinated, twenty-year-old man in Rockland County, New York, developed fever, abdominal pain, and neck stiffness. A few days later, he struggled to move his legs. He presented to a nearby hospital, where he became the first person in nearly a decade to be diagnosed with polio in the United States. Polio can be prevented, but not cured.
Because most cases of polio do not paralyze, a single case of paralysis suggests that the virus could already be widespread. According to public-health officials, hundreds may have been infected, and the virus is now sloshing around in New York City wastewater. “I think it’s safe to assume that this case represents the very tip of the iceberg,” José R. Romero, the director of the National Center for Immunization and Respiratory Diseases, told me. The Centers for Disease Control and Prevention calls the situation a public-health emergency.
New York is not alone. The ancestral strain of polio has never been eradicated in Afghanistan or Pakistan, and, earlier this year, more than a year after Africa was declared free of it, the virus paralyzed children in Malawi and Mozambique. (In 2011, the C.I.A. organized a fake hepatitis-B vaccination campaign in Pakistan with the goal of finding Osama bin Laden; revelations of the covert program subsequently destroyed trust in immunization, and dozens of vaccinators were killed.) In Ukraine, polio has paralyzed at least nineteen people this year. In Israel, eight cases of polio in children were reported in the spring. In June, after the virus was detected in London sewage samples, authorities declared a “national incident” and offered polio booster shots to all children who live in the city and are between the ages of one and nine.
For people who are vaccinated, the virus poses little risk: a complete series of polio immunization is more than ninety-nine-per-cent protective against systemic disease. Because ninety-three per cent of children in the U.S. are vaccinated—well above the threshold for herd immunity—we won’t see anything like the horrifying twentieth-century outbreaks that paralyzed thousands of Americans each year. Still, in communities with low immunization rates, the virus could cause considerable, completely avoidable damage. In Rockland County, which is home to a large Orthodox Jewish population that has been targeted by anti-vaccine activists, only sixty per cent of young children are immunized. In some Zip Codes, barely a third are. (Although every state requires polio vaccination to attend public schools, in some cases parents can obtain religious or personal exemptions, and many delay having their children immunized until they start kindergarten.)
In the worst case, these outbreaks could be more than a temporary setback: they could undermine years of hard-won progress that very nearly eradicated the virus globally. “I’m really concerned we’re going to see more cases,” Walter Orenstein, the associate director of the Emory Vaccine Center who previously directed the National Immunization Program, told me. “We can’t just be reassured by high vaccination rates in the country as a whole, because subpopulations with low coverage can sustain transmission.”
The poliovirus is wildly contagious and usually spreads through contaminated food or water. Once infected, a person can shed the virus for more than a month, even if they are asymptomatic. The virus dwells primarily in the gastrointestinal tract but occasionally migrates to the central nervous system, where it can inflict devastating, sometimes permanent damage. Up to five per cent of people infected will suffer meningitis, or inflammation of the protective membranes around the brain and spine; as many as one in two hundred people will develop paralysis, usually of the legs, but sometimes of the muscles that allow us to breathe, leading to respiratory collapse. (The world’s first intensive-care units were developed, in the nineteen-fifties, to treat polio.) Decades after an infection, as many as half of survivors may experience progressive muscular weakness and pain, known as post-polio syndrome.
Unlike coronaviruses and monkeypox, poliovirus has no animal reservoir—it infects only humans. Because it cannot take refuge in other species, it is unusually vulnerable to eradication, and in recent years we’ve come tantalizingly close. In 1988, when the Global Polio Eradication Initiative was launched, there were around three hundred and fifty thousand polio cases a year across more than a hundred countries; the virus paralyzed a thousand kids a day. Since then, the incidence of polio has decreased 99.9 per cent; in 2018, there were just a hundred and thirty-eight cases worldwide. The vaccination campaign is believed to have averted more than two million cases of paralysis.
Military conflicts, migration patterns, and humanitarian crises have all contributed to polio’s spread, but fundamentally, vaccine-preventable diseases rise when vaccination rates fall. During the COVID-19 pandemic, the world has experienced its largest decline in childhood vaccinations in three decades. In 2020, when dozens of countries experienced a months-long pause in polio-vaccination efforts, at least eleven hundred children were paralyzed. In 2021, twenty-five million children missed at least one dose of routine immunizations. Meanwhile, the anti-vaccine movement continues to gain purchase.
“This really should be a call to action for parents,” Ashwin Vasan, New York City’s health commissioner, told me. “We’re trying to raise the alarm here.” Vasan, whose uncle was paralyzed by polio and whose aunt died of it, in India, said that “there’s no doubt anti-science and anti-vaccine movements have gained power and visibility in recent years. And now, in social media, they have a misinformation superhighway through which they can disseminate their message.”
One response to global misinformation campaigns is hyperlocal action. Research suggests that decisions to get immunized can be less about individual analysis of risks and benefits, and more about the social norms: when people think that others around them are getting vaccinated, they’re more likely to get vaccinated themselves. Public-health officials should enlist trusted figures from within communities who can speak directly to people’s questions and concerns. It may also be possible to immunize people against misinformation, with campaigns that train the public to recognize its many forms. Health-care providers can try a technique known as motivational interviewing, which explores the reasons for a person’s ambivalence and guides them toward positive behavior change. In other cases, governments and clinicians need to lower the practical barriers to vaccination by making it accessible, convenient, and free.
The story of polio immunization, while remarkably successful on the whole, also includes an inconvenient truth: the majority of cases are now caused by “vaccine-derived polioviruses,” which evolved from a live vaccine. For decades, most of the developing world has depended on the oral polio vaccine, or OPV, invented by the medical researcher Albert Sabin, which uses a weakened virus to generate an immune response. The vaccine is cheap, accessible, and extremely effective: a dose costs a few cents and is administered by squirting a couple of drops in the mouth. Once immunized, people may shed the harmless virus, which, in areas of poor sanitation, can actually be a good thing: unvaccinated people are exposed to the non-threatening version and gain immunity, too. But, in rare cases, if the weakened virus is able to circulate in under-immunized communities for an extended period, it can gradually mutate into a virulent form that causes illness. Genetic sequencing linked the case in New York, and the polio in Jerusalem and London wastewater, to a vaccine-derived poliovirus.