Ideas | Thomas Levenson

The world defeated smallpox. Why does polio still exist?

When fighting a disease is a geopolitical priority, we find a way to make it happen.
Lorenzo Gritti for the Boston Globe

ALI MAOW MAALIN was a handsome man. You can see that in a photograph taken in 1977, when he was just 23. He’s shirtless, standing erect, his head tilted forward as he peers towards something the viewer cannot see.

Those good looks aren’t what drew the photographer’s eye, though. The image centers on a scattering of blemishes running up his right arm and across his chest. The blisters are more or less round, and it’s possible to pick out the indentations in many of their centers — obvious signs for those few who still knew how to read them.

Maalin had put himself in harm’s way. A health care worker responding to an outbreak of infectious disease in southern Somalia, Maalin had driven two sick children to an isolation camp in a nearby town. The three were together in the car for perhaps 15 minutes — long enough, it turned out, for the infection to pass from passengers to driver.

Getty Images
Ali Maow Maalin, the last known person in the world with smallpox, in Merka, Somalia.

Maalin was lucky: The virus that entered his body that day was a relatively mild version of a usually much deadlier pathogen, and he recovered swiftly. He infected no one else, and the others within this disease cluster hadn’t either. No new outbreaks followed (though two more cases were to come in 1978 as a result of a laboratory error). Months went by, and then a year, and another. Finally, the conclusion was clear. On May 8, 1980, the World Health Organization announced that, for the first time, a human infectious disease had been completely eradicated. Ali Maow Maalin had been the last person to be infected by the naturally occurring form of what was once one of humankind’s most devastating scourges: smallpox.

So far, smallpox remains the only human pathogen to be eliminated from nature. But now, we may be on the verge of the second such eradication. In living memory and on every continent, the poliomyelitis virus ravaged lives. Polio was and remains, terrifying — causing lasting weakness, paralysis, and death.

As recently as the 1980s, an estimated 350,000 in 125 countries people came down with polio each year. Like smallpox, however, it is a vaccine preventable disease. In 1955 Jonas Salk announced his injectable “killed” formulation, and seven years later that discovery was followed by the Sabin vaccine, which deploys a live but weakened virus to create immunity, and which, usefully for a global campaign, could be given to children on a sugar cube. The the new vaccines showed their power immediately. US polio infections peaked at over 50,000 in 1952, then dropped to just 61 in 1965, and to zero in 1979. That regional triumph, and other such polio success stories led the WHO to announce in 1988 that it would target the disease for global eradication by 2000.

The WHO missed that deadline as it has each subsequent one. There have been advances, extraordinary ones. Two of the three wild forms of the disease are completely gone from the world. Polio today remains endemic in just three countries: Pakistan, Afghanistan and Nigeria — and there were no new infections in Nigeria last year. There have been tragic setbacks. Because the oral vaccine uses a weakened version of live polio virus, it can, on occasion, mutate into full blown infectious disease. In Syria, where the ruination of the civil war creates the perfect conditions for the spread of infectious disease — wrecked water systems and interrupted vaccination campaigns — vaccine-derived polio has recurred repeatedly, most recently last summer, in a five-month outbreak that left at least 17 children paralyzed.

That episode is a brutal reminder: Until a disease is wholly gone, it remains a threat. If polio were to break out of its last reservoirs, then, according to one official estimate, there could be as many as 200,000 new cases per year as soon as 2030.


In all, the effort to eliminate polio has now taken 30 years and counting — almost two decades more than originally planned, and three times as long as it took to get rid of smallpox.

Every disease is different and presents distinct biological challenges, of course. But the different courses of the smallpox and polio campaigns point to another harsh truth: Public health is as much a political challenge as it is a medical one. In polio’s tenacious survival we can trace the historical evolution of a world in which it is, for now, getting harder to mount collective action for the common good.

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The goal of global eradication dates back to the invention of the first successful smallpox vaccine. In 1796, an English country doctor named Edward Jenner used material from a related illness, cowpox, to inoculate James Phipps, the 9-year-old son of his gardener. He then exposed the boy to smallpox, several times. Phipps never became ill, and after several more trials, Jenner published his results, then dared to dream. In 1801, following the first widespread successes proved the value of his vaccine, he declared, “it now becomes too manifest to admit of controversy, that the annihilation of the Small Pox, the most dreadful scourge of the human species, must be the final result of this practice.”


It would take a century and a half before that ambition became the official, stated goal of those with the capacity to achieve it. To do so, the still-young WHO had to learn a hard lesson. As the agency began to consider eradication, the most common tactic for such public health campaigns was mass vaccination. But even before global eradication became the target, it was known that mass vaccine campaigns were inefficient, costly in both money and, sometimes, human suffering.

The erosion of prestige and authority of a scientific or a technical view of the world has also contributed to polio’s persistence.

In 1947, for example, Eugene Le Bar, who had been living in Mexico for several years, took a bus to New York City. He felt fine when he boarded the bus, but began to feel just a little sick that evening — a headache, and some neck pain. On arrival, he checked into a hotel, went sightseeing, browsed through a big department store. About a week after he set out on his journey, Le Bar entered the hospital, with his smallpox infection still undiagnosed, and five days later he was dead.

Le Bar was patient zero for an outbreak — but the entire chain of infection only reached 11 more people, one of whom died. But by 1947, many New Yorkers lacked immunity to the disease, as smallpox had not been a local threat for decades. The return of a legendary killer sparked a mass vaccination campaign. Over 6 million people were dosed. Six of them died. At the same time, wholesale vaccination campaigns were proving less effective than needed. Epidemiologists found that as long as enough of a population evaded the vaccinators, a reservoir of the disease would remain. Any previously safe region would be vulnerable, as New York was in 1947.

Thus, in 1967, when the WHO launched its full, world-wide assault on smallpox, the move came with a shift in strategy. Instead of trying to vaccinate every person in a country or a region, public health officials began to concentrate only on places where smallpox actually appeared. This watch-and-react approach, combining disease surveillance with a localized push to vaccinate any unprotected person nearby whenever a smallpox case appeared, applied with increasing precision once the global effort started in earnest. It led directly to Somalia in 1977, that last spray of infection within a single, tiny community of nomads, and to Maalin, himself, the final person to encounter in the wild what had so recently been humanity’s “most dreadful scourge.”

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A Syrian child receives a vaccination against polio during a campaign organised by the Syrian Arab Red Crescent (SARC) in the rebel-held area of Eastern Ghouta, on the outskirts of the capital Damascus, on February 22, 2015. AFP PHOTO / ABD DOUMANY / AFP PHOTO / ABD DOUMANY (Photo credit should read ABD DOUMANY/AFP/Getty Images)
A Syrian child receives a vaccination against polio.

That’s the conventional account, and it’s true as far as it goes — skilled, dedicated and resourceful public health officials adapted to circumstances on the ground and achieved a tremendous victory. But there’s much more to the story than dedicated disease detectives and heroic vaccinators. The WHO officially committed itself to the elimination of smallpox only when the Soviet Union rejoined the agency in 1958. The Soviet delegation proposed a five-year plan to eliminate smallpox at the next plenary meeting, offering 25 million doses of the vaccine to get things started. There were certainly pragmatic reasons behind the Soviet offer: Smallpox had been eliminated within the country in the 1930s, but had re-emerged repeatedly as travelers brought contagion with them. But the move was also a Cold War exercise of soft power. This signal of Soviet concern for the world’s poor and ill was intended to draw a rhetorical contrast to the capitalist West.

The United States countered in the next decade. Even though the WHO had officially launched the eradication campaign in the late 1950s, there was almost no money directed to that commitment. Little happened until 1965, when President Johnson announced a hugely ambitious plan to take the Great Society global. During this era any public display of good intentions by the United States or Soviet Union always carried an obvious subtext. But the work made possible by such cut-and-parry was real and vital. Once Washington announced its full support for smallpox eradication — with cash attached to the commitment — the WHO managed, within a little more than a decade, to end smallpox.

In some sense, this first eradication of human pathogen was the happy result of the Cold War. In a bipolar world, ideological competition and the muscle of the two superpowers were crucial in getting good works done.

Yet the smallpox campaign revealed another reality of the post-war era: International institutions could be agents of valuable change across borders. Throughout the effort, Americans working on smallpox eradication under the umbrella of the WHO were able to work effectively in countries aligned with their Soviet rivals. The faith that the cause transcended politics could be both sincere and persuasive.

But by the time smallpox was finally declared gone, in 1980, the circumstances boosting the work of eradication had already begun to shift. In the ’80s, the Cold War was coming to its uncertain end, and the international system was no longer clearly organized around any two poles. The United Nations had long since seen its post-World War II gleam and grand ambition erode.

What this meant has became evident in how the next great eradication campaign has played out.

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The declared, international war against polio has taken 30 years old and counting, three times as long as it took to rid the world of smallpox. There is no single, reductionist explanation for the extraordinary difficulty in getting to zero. But the way the world has changed between the two efforts is at least part of the story The ideological competition that helped spur the superpowers to fund international efforts ended with the Cold War — and a shortage of cash contributed to the drop in polio vaccination in India in the early years of the new century.

Local and regional conflict, often fueled by cross-cutting international interference, offered opportunities for the disease as well. Vaccine-derived polio thrives where water supplies and sanitation are compromised, where the two-dose cycle of oral vaccine gets interrupted, where medical personnel can’t reach everyone at risk. In other words in a war-zone. In the 2017 Syrian outbreak, 74 people were infected, more than triple the number of wild polio cases. In the last years of the smallpox campaign, public health workers had to navigate the local conflicts of the Horn of Africa. Syria is our latest reminder that infection loves war.

The erosion of prestige and authority of a scientific or a technical view of the world has also contributed to polio’s persistence. Rumors that the polio vaccine might cause women to lose the ability to bear children shut down vaccination campaigns in parts of Nigeria and elsewhere and led to the murders of some vaccinators.

Pakistani suspicion of vaccinators deepened when, as US intelligence services hunted for Osama bin Laden in 2011, a possibly unwitting Pakistani physician, Dr. Shakil Afridi, was recruited to try and use a vaccination effort to confirm bin Laden’s location. Afridi was enlisted into a campaign against hepatitis B and was tasked to with visiting the house in which it was suspected bin Laden might be hiding, vaccinating, then hanging on to the used needles to supply DNA for the CIA to test.

Afridi failed to gain access to bin Laden’s household, but the story shattered trust in vaccine efforts in Pakistan. Nine vaccinators were killed shortly after the bin Laden news broke, and as recently as mid-January of this year, a mother-daughter team in Quetta, Pakistan, were gunned down while they were giving oral polio doses to local children.

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Despite that attack Pakistan is continuing with broad polio vaccine efforts, and the disease does appear to be almost gone. There were just 22 wild-polio infections worldwide last year, all in Pakistan and Afghanistan. So far in 2018, there have been only two new cases, both in Afghanistan. It’s conceivable that polio incidence may drop to zero before the end of the decade.

If and when that occurs, it will be a monument to the power of public health work. But the question will remain: Why was the end of polio so long in coming? It wasn’t because, after solving smallpox’s riddles, human reason couldn’t solve the problem, or that science or medicine failed. Rather, it was because such achievements exist within history, the way human beings construct our world at any given time.

The history still being made of polio eradication reveals the costs that follow when the ability to pursue common goals degrades within and between nations. Infectious disease, pollution, and conflict itself do not respect borders, not even those of countries that build big, beautiful walls.

There is one last story, a small, sad one, that captures the reality of interconnection, of the need to rebuild the ability to think and work globally. Ali Maow Maalin, wild smallpox’s last host, recovered, married, and with his wife raised three children. When the polio eradication campaign began in Somalia in 1997, he signed up again. In 2004 he became an official vaccinator, and with his colleagues, was able to celebrate the elimination of the disease from his country in March of 2007.

Then, after six polio-free years, it returned. An outbreak flared in the spring of 2013. Maalin resumed work as a local polio organizer, but on his second day on the job, he fell ill. He shrugged off his ailment until he became too weak to continue. He had contracted malaria, in a sudden and violent presentation. Within days, on July 22, 2013, he was dead.

Polio didn’t kill him, not directly. But it was polio that put him in harm’s way, six years after he had every reason to believe it had been banished from his home. No matter how it returned — overland from Nigeria perhaps, or across the Gulf of Aden — Maalin’s death is a reminder: We can’t run and we can’t hide. We have no choice but to act across even our most fortified boundaries against the peril that viruses and microbes and winds and water carry where they will.

Thomas Levenson is a professor of science writing at MIT and an Ideas columnist. His latest book is “The Hunt for Vulcan.”