Sixty years after the polio vaccine became widely available, mass vaccinations continue around the world. (Photo: Asianet-Pakistan/Shutterstock)

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In the past month, Oxford University, three African countries, and American pharmaceutical giants Johnson and Johnson and GlaxoSmithKline have begun testing Ebola vaccines on human subjects. At the height of the West African Ebola outbreak last year, observers questioned why a vaccine was not yet available; since then, progress to testing has occurred at warp speed. Meanwhile, optimistic reports have gone so far as to conflate a vaccine with eradication or suggest that eradication might occur this year.

The current outbreak in West Africa will likely slow or stop within months, and the issue is already fading from public consciousness. But this does not mean the disease is anywhere near being wiped out—no matter what clickbait titles might claim. Eradication, by definition, means ending the possibility that the disease can infect anyone worldwide ever again, and that’s not something an Ebola vaccine can guarantee.

Rather, the process of testing, producing, and implementing a vaccine will take years. In fact, it might take decades—if it happens at all. Only one human disease has been completely eradicated: smallpox. Instead, as we barrel toward an Ebola solution, the history of polio may give us an idea of what to expect. Over 60 years since the development of an effective polio vaccine and 27 years after dedicated eradication efforts began, several countries still suffer outbreaks.

If anyone had told New Yorkers in 1957 that polio would still be with us today, it might have come as a surprise. In that decade, the word “polio” (or the disease’s earlier name, infantile paralysis) was constantly present in American conversations. “One of the most common mantras of the post-World War II era, repeated by fundraisers, politicians, advertisers, and journalists, was the bold (and ultimately) truthful promise, ‘We will conquer polio,’” writes David Oshinsky in Polio: An American Story.

The disease itself is ancient—an Egyptian tomb dating back to 1191 B.C.E. houses a pharaoh with a withered leg, a common post-polio disability—and its first scientific documentation dates back to 1789. But in the early 20th century, changes in water sanitation shifted the infection from a mild infant illness to a disease that swiftly struck children and adults without warning. Oshinsky called it “the most feared disease of the twentieth century.” In 1952, the year of the worst U.S. outbreak, nearly 58,000 cases left more than 3,000 people dead and more than 21,000 others paralyzed. Public fear catalyzed some of the most popular fundraisers in American history. U.S. President Franklin Delano Roosevelt, himself a polio survivor, championed the fight against the disease. By 1957, a vaccine discovered by researcher Jonas Salk became widely available, saving millions of lives. Joy reverberated from the halls of Congress to elementary school classrooms—a reversal of the sustained panic of years before.

To a degree, the current attention to Ebola feels like polio’s history repeating itself. Ebola emerged in 1976 in the Congo, and decades passed with relatively little attention. In 2014, a large shift in infection patterns made Ebola hemorrhagic fever an early front-runner for the most feared disease of this century. It's currently claiming lives at high speed—of the current outbreak's 21,121 victims (as of January 7, 2015), 8,301 have died. The demand for effective prevention rings loud and clear. Innovative efforts to fight the disease have received widespread attention, and prominent people (including uber-philanthropists Bill and Melinda Gates) are backing the race to develop a vaccine. When one is developed, many people will rightfully rejoice.

But if history repeats itself, it could be a long time before the number of Ebola cases drops to zero. Nearly six decades after Salk’s polio vaccine became widely available, people are still lining up for a dose of it. In Pakistan, Afghanistan, and Nigeria, polio outbreaks continue. This is not for lack of effort. In 1988, the World Health Organization’s Global Polio Eradication Initiative aimed to lower the number of cases worldwide to zero by the turn of the millennium. They failed. In a foreword to The End of Polio, a 2003 essay collection with photographs by Sebastião Salgado, former United Nations secretary general Kofi Annan mentions “the internationally agreed upon target date of 2005” for polio eradication but calls the aim “by no means assured.” His caution was justified: The eradication effort rolls onward now, a full decade later, having contacted as many as half a billion children at once, involved millions of personnel, and cost billions of dollars.

Incredible headway has been made in the fight against polio. Two of the three types of the virus are no longer causing infections, and the number of cases per year has hovered in the mid-hundreds for a decade, a stunning fall from the 350,000 people infected in 1988. But that has not been quite enough. As Siddharth Dube remarks in The End of Polio, “There is a virtual consensus that there is no choice but to continue high rates of global immunization against polio for the foreseeable future.” Abandoning the effort would mean a massive resurgence of paralysis and death.

Will Ebola linger on the same way? The answer depends on many factors. First, we’ll need a vaccine. “We’ve been working at an unprecedented pace together with our partners,” Matthew Snape of the Oxford Vaccine Group said when the Johnson & Johnson trial was announced. But luck plays a role in every scientific development. GlaxoSmithKline company representative Jenni Ligday said, “At this stage in development, it is too early to know exactly when the vaccine might be available.”

Early studies of poliovirus, for example, unwittingly attempted to infect a primate subspecies that could not contract polio in most body tissues; the resulting misunderstanding delayed vaccine development for 14 years. Other vaccine efforts, most notably for HIV, have temporarily lapsed when biological hurdles proved insurmountable.

In the past, the main block to an Ebola vaccine has been lack of political will. “But now,” WHO doctor Sally-Ann Ohene says, “the world at large is paying attention.” The threat of Ebola infections in the West, where pharmaceutical companies can hope to recoup research and development expenses, reversed this long-standing neglect—and that could be a boon if the resulting vaccine becomes accessible worldwide. “All agreed on the ultimate goal: to have a fully tested and licensed product that can be scaled up for use in mass vaccination campaigns,” according to an October 2014 press release from the WHO. “The next step is to make these vaccines available as soon as possible—and in sufficient quantities—to protect critical frontline workers and to make a difference in the epidemic’s future evolution.” This challenge, however, is formidable.

The emergence of Ebola outside of Africa is “a matter of where and when,” per ecologists interviewed by NPR this month. To achieve full eradication, we may need to vaccinate the entire world population.

To begin, the area of coverage may become large. Previously, the disease was confined to rural sub-Saharan villages; this past outbreak saw Ebola reach Africa's mega-cities and distant continents. While many fear Ebola’s spread via air travel and a few have gotten paranoid about bioterrorism, the real threat of Ebola in the skies is from the disease’s animal vector: bats. Recent testing established that bat species in Bangladesh have antibodies similar to Zaire strain Ebola, which means the emergence of the disease outside of Africa is “a matter of where and when,” per ecologists interviewed by NPR this month. To achieve full eradication, we may need to vaccinate the entire world population. GSK’s Ligday notes, “Mass vaccination campaigns will depend on ... how quickly large enough quantities [of vaccine] can be made.”

Logistics are also a key factor in vaccine distribution. While there has long been an effective polio vaccine, it requires an oral dose four times over successive months. On each occasion, the vaccine must be kept refrigerated at all times to keep the doses from spoiling. That’s no mean feat in places like the Congo, where equatorial temperatures can be blistering hot and electricity is spotty at best. While Ebola is not biologically similar to polio, it, too, may require special attention and repeated doses. (At present, at least one vaccine is being tested as a series of two injections.)

Worse, it may require braving warfare. “Polio is one of these hounds of war,” The End of Polio essayist Dube writes. The Congo suffered a polio outbreak in 2010 that infected 445 people and killed 209. Although that epidemic was a biological rarity, the country shares a trait with polio-endemic nations Afghanistan, Pakistan, and Nigeria: armed conflict. This alone does not make breaking transmission impossible; other countries have endured warfare without polio relapse. But violence interrupts vaccination campaigns and increases disease outbreaks of all kinds, from polio to Ebola and beyond. The last place polio returned after transmission was broken? Syria.

Of the three West Afr­­­­ican nations most affected by Ebola, two (Liberia and Sierra Leone) have experienced recent civil wars, and a relapse into violence is not beyond imagination. “These things tend to bleed into each other,” infectious disease and violence expert Gary Slutkin told me.

Will Ebola be eradicated? If it is, it will be only the second human disease ever wiped out. The first was smallpox, which ceased infecting humans in 1977. Like Ebola and polio, smallpox was a virus that imposed extreme, sudden suffering on its victims, seemingly at random. Its eradication was aided by factors that differ from polio, including a single-dose vaccine and a lack of contagiousness after an infected person recovers. For those reasons, the campaign for total global vaccination took only two decades. With luck, eradication of Ebola could proceed as quickly.

Then again, smallpox had a factor that Ebola can’t offer: There was no animal vector. Humans caught the disease from other humans alone, and breaking transmission forever simply required vaccinating humans. Ebola is different, a disease of the forest. It’s thought to exist in bats, primates, and other animals. Eradication could mean eliminating the reservoirs of viruses in all other affected species, a task with dimensions even more gargantuan than vaccinating every human.

Whether or not eradication is a wise idea is debatable, too. As polio begins to vanish from the planet, the disease has become rare—and yet every child born still has to be vaccinated against it. The number of vaccinations necessary to avert each active case has risen exponentially. As Atul Gawande writes in his 2007 book Better: A Surgeon’s Notes on Performance, “Stopping the very last polio case might cost as much as $200 million dollars.” For Ebola, it may be more feasible to use targeted mass vaccination campaigns to break transmission wherever outbreaks occur— indeed, Ligday says that Ebola vaccines will be used for “targeted vaccination of additional health care workers and other people at high risk of infection” if trials are successful.

For now, “Ebola eradication” remains a simple misnomer, a step further than we could possibly plan. Transmission probably will be broken this year in West Africa, mostly with the tried-and-true methods: contact tracing, quarantine, treatment, and safe handling of the dead. Meanwhile, the world will continue its race toward an effective vaccine, and the world will figure out all over again how to collaborate in fighting a fearsome disease.