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Before its discovery in New York’s wastewater, the virus made a series of ominous appearances around the world. At the beginning of this year, there was a thrum of excitement among global health experts: Eradication of polio, a centuries-old foe that has paralyzed legions of children around the globe, seemed tantalizingly close. Pakistan, one of only two countries where wild poliovirus still circulates, had not recorded cases in more than a year. Afghanistan had reported only four. But eradication is an uncompromising goal. The virus must disappear from every part of the world and stay gone, regardless of wars, political disinterest, funding gaps or conspiracy theories. New signs of the virus in a single country can derail the effort. In polio’s case, there were several ominous setbacks. Malawi in February announced its first case in 30 years, a 3-year-old girl who became paralyzed following infection with a virus that appeared to be from Pakistan. Pakistan itself went on to report 14 cases, eight of them in a single month this spring. In March, Israel reported its first case since 1988. Then, in June, British authorities declared an “incident of national concern” when they discovered the virus in sewage. By the time New York City detected the virus in wastewater last week, polio eradication seemed as elusive as ever. “It’s a poignant and stark reminder that polio-free countries are not really polio-risk free,” said Dr. Ananda Bandyopadhyay, deputy director for polio at the Bill & Melinda Gates Foundation, the largest supporter of polio eradication efforts. The virus is always “a plane ride away,” he added. Polio is a highly contagious and sometimes deadly enemy, capable of ravaging the nervous system and causing paralysis within hours. Those who recover could relapse and become seriously ill years later.
The virus multiplies in the intestine for weeks and could spread through feces or contaminated food or water — for example, when an infected child uses the toilet, neglects washing hands and then touches food. For decades the virus terrorized families, causing paralysis among more than 15,000 American children each year and hundreds of thousands more worldwide. Its retreat is a triumph of vaccination. After the first vaccine arrived in 1955, the number of cases dropped precipitously, and by 1979 the United States was declared polio-free. Although the United States and Britain have high immunization rates, they also have pockets of low immunity that allow the virus to flourish. In those communities, all unvaccinated people — not just children — are at risk. If polio continues to spread in the United States for a year, the country may lose its polio-free status under W.H.O. guidelines. The Covid-19 pandemic left many other countries vulnerable to a resurgence of polio: It disrupted vaccination drives for months and diverted staff and resources away from prevention programs, resulting in the worst backslide in immunization rates in 30 years. “The moment you take your eye off the ball, you know that the virus will simply reappear,” said Aidan O’Leary, director for polio eradication at the World Health Organization. “We have to literally face down every single chain of transmission that we can identify.” Aid organizations first aspired to eradicate polio in 1988 and poured billions of dollars into the Global Polio Eradication Initiative, a consortium of six partners, including the Gates Foundation, the W.H.O. and the Centers for Disease Control and Prevention. Despite the recent cases, the progress is unmistakable: Global cases of polio have fallen by 99 percent — from 350,000 cases of paralysis in 1988 to about 240 so far this year.
That success “is both a miraculous thing and a thing that’s taken way, way longer than people expected,” said Bill Gates, who has taken a pointed interest in polio, in an interview in February. “Eradications are super hard, and they rarely should be undertaken.” Ending polio has been particularly challenging. There are three strains of the wild poliovirus. Type 2 was declared eradicated in 2015, and Type 3 in 2019. Only Type 1 poliovirus remains at large, and only in Pakistan and Afghanistan. Until recently, there was good reason to be optimistic about Type 1’s demise. India and Nigeria were both considered impossible targets for polio elimination, but both achieved that goal. “There were so many people who kept telling us you will never succeed in India,” said Dr. Hamid Jafari, W.H.O.’s director of polio eradication for the eastern Mediterranean region. Afghanistan and Pakistan have proven more difficult because of their nomadic populations, rough terrain and the baseless notion that the vaccine is a Western tool for sterilizing the population, Dr. Jafari said. In Afghanistan, polio thrived in areas where immunization bans were imposed by the Taliban. In late March, the Taliban allowed vaccinations to resume, but the doses are administered in door-to-door campaigns, often by female health care workers. Some have been assaulted and killed. Only one human viral disease, smallpox, has ever been eradicated. For all its deadliness, smallpox was relatively simple to dispatch because every infection resulted in dramatic, unmistakable symptoms. Polio is much more sly: It can spread silently, causing mild flulike symptoms or none at all, and yet the disease paralyzes one of every 200 infected children. Even one case of paralysis is a signal that there may be hundreds or even thousands of undetected infections. “Paralysis is the tip of the iceberg,” said Dr. Walter Orenstein, associate director of the Emory Vaccine Center and a former director of the United States’ Immunization Program. But in some countries, polio has become such a dim and distant threat that health officials have stopped looking for it. While Britain and Israel monitor sewage for the virus — ideal because polio spreads through fecal matter — many others, including those in the United States, have ceased active surveillance. “There’s no doubt that there are places where it needs to be reinforced,” said Dr. Matshidiso Moeti, W.H.O.’s regional director for Africa....
