Epidemics in Western Society Since 1600

HIST 234 - Lecture 24 - Poliomyelitis: Problems of Eradication

Chapter 1. Polio [00:00:00]

Professor Frank Snowden: Good morning. We can start. Today we’ll be discussing poliomyelitis, or polio for short. And you may be wondering why we’ve included it at this point, late in the day in our course. And that’s because a number of you have been saying that you’d like to have the course come right up to date and today’s newspapers, and the way I want to deal with polio, I hope, is in light of that request. In other words, we’re going to be dealing with polio at this very moment; and in particular with problems of vaccination, that very major public health strategy.

The subject will really be the problems facing the Global Polio Eradication Initiative which, just to remind you, is the largest public health campaign ever launched. It predicted global eradication by 2000. And when it began in 1988 it used as its model the eradication of smallpox, as you know pioneered long ago by Edward Jenner, and actually reaching successful conclusion in 1980 when the World Health Organization certified that the world globe was free of naturally occurring smallpox. There seemed to be a number of reasons that smallpox could be taken as the model. This was the first disease, and still the only one, major disease, actually eradicated intentionally by human beings, by a public health campaign.

It was thought that polio had a number of features that made it a similarly good candidate, just like smallpox. It was a disease, like smallpox, that possessed no animal reservoir. So, if you got rid of it in the human population, it wouldn’t again jump species and recur through transmission from animals to humans. It was also a viral disease, and the pathogen has no complicated lifecycle. It’s at the other end of the spectrum from, for example, the malarial plasmodia. The acquired resistance is robust, produced by the body naturally. That was true of polio, as it is of smallpox. And it was the case that just as in the example of smallpox, so too with polio there seemed to be a very robust and powerful tool; that is, two vaccines, one injected — we’ll come back to that — and the other oral, the polio vaccines.

But as we speak, the global eradication program has run into serious and unexpected difficulties. After it was originally launched in 1988, it went from success to success, and seemed to be poised for successful eradication, if perhaps not by its original timetable of 2000, well then perhaps just a little bit later. But in 2003 major difficulties overtook the campaign — and we’ll come back to those — and now the campaign is a decade behind schedule, and the elusive goal of global eradication seems to be receding, rather than becoming closer. It stalled particularly in four endemic countries — India, Afghanistan, Pakistan and Nigeria — and even spread, particularly from Nigeria, to an array of other countries.

So, the question is whether this stalling is temporary and for contingent reasons likely to be overcome, or was eradication on the smallpox model a mirage from the start? And this can be personified in a major debate between two leading figures in international public health. One is Bruce Aylward, who’s the director general of the Global Public Polio Eradication Initiative. He’s a great optimist, and says that the problem is simply a matter of pressing harder when difficulties emerge, and he envisages eradication in short order. Then there’s D.A. Henderson, and he was the former director of the successful Smallpox Eradication Program, and he was the director of polio eradication in the region of the Americas. Originally he was a very enthusiastic eradicator, but now he’s come round to the view instead that eradication was a mistaken concept from the start; that it will simply never work with polio, which is totally unlike smallpox.

This morning, fortunately, we don’t need to make a decision, and hopefully Aylward will be successful. But I do think we need to understand how difficult the eradication of a disease actually is, and to remember how exceptional smallpox is as a case. Polio reminds us that smallpox was an outlier, rather than the norm. Furthermore, the polio problem is intellectually interesting, and we ought to understand it in order to comprehend tomorrow’s press reports on why eradication perhaps didn’t succeed, if that’s the outcome. I don’t want to make a prediction because I’m mindful of that great sage, Yogi Berra, who had a saying, “never make a prediction, especially if it’s about the future.”

In any case, we don’t know whether polio will be eradicated or not. I tend to be a skeptic, but I really hope I’m wrong. The poliovirus has three types, polio 1, 2 and 3, and it enters the body via the mouth, perhaps through contaminated food or water, or in unsanitary conditions with direct contact with stools, or with the secretions from the throat of a patient. The virus then settles in the intestinal tract and it multiplies there. And that’s a picture of the poliovirus. After an incubation period of one to five days, it then settles in lymphatic tissue, along the intestines and in the lymph nodes.

Now, normally the virus does no appreciable harm in the digestive tract, producing nothing more than some swollen lymph nodes. And apart from that, the infection can be totally asymptomatic. In some cases it leads to minor symptoms — these are brief — such as a mild fever, and other symptoms that would make you think of seasonal influenza: headache, nausea, vomiting. Then the patient recovers with nothing more occurring. And that’s true then of the vast majority of cases that end in that way. And indeed, in the historical literature, this was termed abortive poliomyelitis, because the infection progressed no further. But in about one percent or so of cases, there’s something much more serious that occurs, which is the involvement of the central nervous system, and that’s where the disease, if it becomes so established, does its serious damage. It destroys nerves, especially in the spinal cord and the brain.

Let me show you a rather — a schematic — rather scary picture of the poliovirus attacking a nerve cell. When this occurs, the results are severe pain, weakness in the muscles, and then paralysis; and the paralysis can be one leg, both legs, the arms, and the respiratory system. The paralysis also is normally irreversible, and often leads to very severe deformity or maiming of the affected limbs. If the muscles involved are those of the respiratory system, the result can be respiratory paralysis and death. Let me show you some images of the work of poliomyelitis.

This is a picture from the 1950s of a child in rehabilitation, with paralyzed legs, braces and calipers. Or we can see this is a poster of the campaign against poliomyelitis. Or this is the iron lung that was used to save the lives of those who had respiratory paralysis, and we can see another iron lung with a child inside. And a terrible picture, that was all too common in the thirties, forties and fifties, which is a whole ward of children in iron lungs. So, this really was a terrible and cataclysmic disease in its severe form.

What about the history? Poliomyelitis used to be called “infantile paralysis.” Until the 1890s, it was regarded as a minor medical and public health issue. It really exploded onto the world as a major public health and medical problem only in the 1890s. That’s not to say that polio was an emerging disease of the 1890s, but I’m going to say that something new happened that transformed awareness of the disease. It was thought then originally to be an exotic and unimportant endemic disease of early childhood. But something happened in the 1890s, and polio began to appear as something different, especially in the Western industrial world. It began to appear as a virulent epidemic disease. It struck older groups of people, adolescents and grownups, as well as infants, and in its wake it left clusters of dead and paralyzed victims.

The first substantial epidemics ever recorded struck Scandinavia, Sweden, in the 1890s; in this country Vermont, in 1894; Scandinavia again in 1905; New York in 1907; Vienna in 1908; and the northeast of the United States in a devastating epidemic in 1916. After that, epidemics of polio became a recurring and terrifying feature of the warm months of the industrial West. In the U.S., for example, polio struck with ever increasing fury, reaching a peak of ferocity in the years 1950 to 1954, and by that time it had taken over from tuberculosis as the most feared disease of the era.

Chapter 2. A Social Disease in Reverse [00:13:33]

Well, what happened? And here I think we ought to be careful. Let’s avoid an error that misled epidemiologists and public health officials, at least until World War II, and that sometimes has misled medical historians since then. The mistake was to think that polio was in some simple way a disease of the affluent industrial nations, of the clean and the prosperous within them. In reality, poliovirus, as we know, is transmitted by the oral-fecal route, and it was ubiquitous in human populations across the globe. But hygienic advances transformed its epidemiology.

The sanitary bulwarks of the modern industrial state prevented children from encountering the virus during infancy and early childhood, and therefore they failed to build an acquired immunity to the disease. As a result, the numbers of susceptible people in populations began to accumulate, and that provided the basis for periodic large-scale epidemics that struck at later ages. There was a distinguished Yale epidemiologist named John Paul who was very active in the middle decades of the twentieth century in dealing with poliomyelitis, and he argued that the disease should no longer be called infantile paralysis. Under the circumstances, he said, that term should be replaced with the phrase “modern polio.” And modern polio, as he called it, demonstrated a strong predilection for relatively prosperous older children, adolescents and adults, and it did so in the economically advanced nations of the world: Northern Europe, North America, Australia, New Zealand.

Polio, in this sense, what John Paul called modern polio, seemed to be — if we could toy with a phrase that’s all too familiar to you by now — it seemed to be a kind of social disease in reverse. That is, it seemed to cause epidemics among the clean, the wealthy and the suburban. And, so, polio became a highly visible epidemic disease that terrified, because it was so visible, because there was no cure, and because everyone seemed to be vulnerable, while the disease itself left in its wake, after each visitation, thousands of people who were maimed and crippled, as well as the dead. But the reality was a little different. Although epidemic modern poliomyelitis increased the pace of its ravages in the Western world, proof soon emerged that polio also imposed an unnoticed but equally heavy tribute of suffering in the resource-poor tropical world.

In other words, this was an illusion that it was only afflicting the industrial, clean world. This caused enormous surprise. The prevailing dogma was that poliomyelitis was an affliction of modernity and sanitation, and was of negligible concern in the developing world. But World War II caused a shock. Suddenly there was the experience of non-immune U.S., British, Australian troops, stationed in places like Egypt or the Pacific, and there, against all expectations, significant numbers of them contracted poliomyelitis. And then this disturbing finding was confirmed by evidence from serological examinations, from rectal swabs, from laboratory analysis of the microbial bounty in Third-World sewers, and by lameness surveys — that is actually counting people who are afflicted by paralysis — in places like India. And the evidence confirmed that paralytic poliomyelitis in the tropics was actually greater than in the developed world, at its height, but that it was unnoticed.

Why was it not noticed? It was not noticed, in part, because physicians and public health officials had long taught not to expect it; everyone closed their eyes. It was also true because the impoverished children of the tropical world had so little access to medical care that they simply weren’t seen; they were invisible. Because the illnesses of the poor were regarded as unremarkable, and because the poor themselves fatalistically expected that their children would suffer and die in disproportionate numbers. Meanwhile, maimed and paralyzed children grew up in the Tropical world to join the ranks of beggars in the streets of Jakarta, Cairo and Lagos.

Well, the poliovirus was discovered in 1908 by Karl Landsteiner — who’s on your handout — but thereafter the natural history of the disease remains shrouded in mystery. Still in 1950, the mode of transmission and the portal of entry of the virus into the body were unknown; as was the issue of whether poliovirus existed in a single strain, or serotype, or in multiple ones. Was there one type or many?

Similarly, the immune mechanisms of the body were not understood. And, in fact, a critical mistake was made that — and this mistake misled the public health community, researchers and medical science for a long period, from the 1920s or so, down to the 1950s — and this was to assume that the course of the disease in human beings was the same as that in monkeys. In other words, there was an extrapolation from the laboratory to human beings. And this mistake had a number of corollaries. It meant that it was assumed that the portal of entry of the virus was the nose, rather than the digestive tract.

It was assumed that the disease primarily attacked the central nervous system, and that the virus made its way from the nose to the spinal cord and the brain, via the nervous system. Well in terms of public health, and the possibility of vaccine development, these conclusions were entirely counterproductive, because they led to a corollary. The corollary was that since the disease spread via the nervous system, rather than the bloodstream, there was no opportunity for antibodies to mount a defense, and therefore no possibility for developing a vaccine.

Then we have an enormous campaign of research and public health against this increasingly feared and terrible disease, and this was with the National Foundation of Infantile Paralysis, and it spawned the March of Dimes Campaign, which collected enormous amounts of money devoted to research, and also to the care and rehabilitation of the victims of poliomyelitis. Let me just show you some images of the collecting of funds in the middle decades of the twentieth century. Or celebrities took part. This is Elvis Presley campaigning for the March of Dimes. Or you can see Elvis again there. And most importantly, one of the most famous, probably the most famous of all polio victims, was President Franklin Delano Roosevelt, who was the leading figure in the establishment of this foundation, and the March of Dimes, and also another rehabilitation center in Warm Springs, Georgia. Let me just remind you that FDR was in fact himself a victim of polio, who was paralyzed.

Chapter 3. Vaccination [00:23:52]

In 1948, a major discovery was made by three men who worked together as a team and shared the Nobel Prize amongst themselves. These were John Enders, Thomas Weller and Frederick Robbins, and they discovered that the poliovirus could be cultured in vitro in non-nervous human tissue. Now, why was that discovery critical? Well, first it meant that the cost of research plummeted, because you didn’t need to have live monkeys to take care of in order to do experiments with the virus. It led soon to the discovery that the digestive tract, rather than the nose, was the portal of entry, and it led to the discovery of a phase in which antibodies could attack the virus in the open bloodstream. And it led to the discovery that poliovirus exists in three different serotypes: poliovirus 1, poliovirus 2, and poliovirus 3. And it was these discoveries that made possible the successful development of a vaccine. And this duly occurred in two major forms.

This was a momentous development. The first was by Jonas Salk, and that was an inactivated injectable vaccine, tested in 1904 and administered successfully en masse in 1955. And Jonas Salk became a national hero and celebrity for this, on the cover of Time Magazine. Everyone talked about him, and indeed he was later to say himself that he didn’t need the Nobel Prize because he was much more famous than the prize itself. Second was another vaccine, a competitor if you like, which was a live oral polio vaccine, developed by Albert Sabin, and tested in 1959 and ‘60, and administered en masse in the 1960s. Now both of these developments were funded by the National Foundation for Infantile Paralysis. You can see the role of the March of Dimes in leading to medical discoveries.

Almost immediately after the development of these two vaccines, the goal of eradication was taken up as an objective. In the 1950s, already, Albert Sabin, for example, made eradication an article of faith. He said the goal — and I’m quoting — “is to completely eradicate poliomyelitis, to eliminate it, to make it disappear, to achieve ultimate eradication.” Well, a major question was which vaccine? Should the campaign be based on Salk’s IPV; that is, the injectable inactivated vaccine? Let me try to fix this in your mind.

This is a picture of Jonas Salk, and as you can see he’s holding — about to vaccinate someone with his injectable inactivated virus. And here we can see him at work. This is how Jonas Salk’s vaccine operates with a syringe. It had a number of drawbacks. It was an effective public health measure and led to a robust immunity. But it was administered by injection, and in terms of being a worldwide public health tool, it required qualified vaccinators, and that made it too complicated and expensive for a worldwide campaign, especially in Third World countries. And since it was a killed vaccine, killed by formaldehyde, it would stimulate the production of antibodies, but it wouldn’t cause what was termed mucosal immunity directly in the human gut.

Then there was the alternative, which was developed by Albert Sabin, which was the attenuated live virus. This had — it was administered initially on sugar cubes that were a couple of drops put on them and then people downed them, especially children. Or else it was a pink liquid that was simply dropped with a dropper down your throat. And that could be administered at a fraction of the cost — as I said, on sugar cubes or as a liquid — and the only skill that was required of the vaccinator was the ability to count to two; because you dropped two drops into the throat. And that’s the — it took half an hour to train a vaccinator using Albert Sabin’s oral vaccine. But equally importantly the oral poliovirus caused a virus to be shed from the intestine into the environment; that is, it took root and flourished in the gut of the people, of the vaccinees, and as they shed they would spread, that is the virus, causing an asymptomatic and harmless infection in the guts of whole communities. Thereby you would raise the herd immunity, even in people who weren’t vaccinated. So, you could miss people with Sabin’s vaccine, and still reach entire communities.

That was the vaccine, the major new tool, with its two different forms: Salk’s injectable vaccine and Sabin’s oral vaccine. But what the campaign relied upon was something in addition to the new scientific tools, and this was a new operational campaign strategy. And the campaign strategy, interestingly, was first devised in Fidel Castro’s Cuba, and the campaign strategy provided a context in which oral polio vaccine could be maximally effective. This was taken up and was called the tool of National Immunization Days. Let’s remember how they started. Instead of limiting immunization to those who received routine vaccinations from their physicians, the National Immunization Days took as axiomatic that there was very limited access to medical care, and so the idea was to not bring patients to the vaccinators but to take vaccine to the people.

In 1962 in Cuba, the grassroots organizations of Castro’s revolution, which were called Committees for the Defense of the Revolution, carried out house-to-house surveys to locate every child on the island of Cuba, and then vaccinators made a return visit to vaccinate every child who’d been located. This procedure morphed in the United States into what were called Sabin Oral Sundays, beginning at Tucson, Arizona. And, as you can imagine, these Sabin Oral Sundays weren’t sponsored by Committees for the Defense of the Revolution, but rather by local and county chapters of the AMA, and its members volunteered their services, alongside those of local pharmacists, county health officials, nurses, school teachers, clergymen, the local press, and housewives. And the vaccine was administered in school buildings.

This campaign, thus structured with the new tool of vaccine and the new organizational strategy of National Immunization Days, successful eradicated smallpox, first in the United States, and then in the Americas. In 1988, the World Health Organization then launched the Global Polio Eradication Initiative. At the outset, it was supported in particular by what was the equivalent of the Gates Foundation of its time, and that is the resources and international structure of the 32,000 clubs worldwide of Rotary International; which was an NGO, as I said, somewhat equivalent in its time to the Gates Foundation of our own day. The campaign also enjoyed the support of the CDC, of international agencies like the G8 — as it was then, it’s no longer that, it’s expanded — the African Union, various national governments, and an army of vaccinators.

From the beginning, the Global Polio Eradication Initiative adopted the strategy of combining Sabin’s oral polio vaccine with Cuba’s operational device of community-wide immunization days. The goal was to provide the most susceptible populations on earth, small children, worldwide, every child on the planet, to be vaccinated with at least two doses of oral polio vaccine. Now, let’s remember what a gargantuan effort this actually was. National Immunization Days were extraordinary events that necessitated the participation of 10 million people in their organization.

Take the example of India, where the National Immunization Days became the largest single public health events in history; when as many as 93 million children were vaccinated on single days. Well, 1988 to 2003, the campaign made huge progress. In 1988, the World Health Organization estimated that there were 350,000 cases, worldwide, of paralysis from polio, and it believed the disease to be endemic in 125 countries. In 1988 itself, transmission was halted in Europe. In 1991, it was halted in the Americas, in 1997, in the Pacific region, and in 2001 there was a world record with a low of 483 recorded cases of paralysis in just four endemic countries: India, Pakistan, Afghanistan and Nigeria.

Let me show you a map. This is 2008, as you can see, and the countries in red are those where polio is now endemic, and the ones in yellow are places that it spread to, from those endemic countries, in 2008. Well, there was a setback in 2003, and what did that indicate? Already vanquished in the industrial world, poliomyelitis, in 2003, remained endemic only in some of the most unsanitary, poverty stricken and insecure places on the planet. This is one reason that it’s a mockery to think of poliomyelitis as a disease of the affluent and the clean. Poliomyelitis had been driven back to the war-torn and remote areas of Pakistan, to Muslim dominated states of northern Nigeria, northern Sindh in Pakistan, and the states of Bihar and Uttar Pradesh in India.

Now, the Muslim states of Nigeria, and especially Kano, as we’ll talk about in a moment, were the most striking cases. There, in northern Nigeria, the campaign was actually halted by a boycott, an organized boycott, for thirteen months. As a result, in Nigeria, the disease flared up, causing hundreds of cases of acute paralysis. And alarmingly it spread from Nigeria widely, causing outbreaks of paralysis in eighteen countries in West and Central Africa, that had previously had been pronounced polio free.

Chapter 4. Challenges to Eradication [00:38:32]

Well, what were the problems that emerged in 2003? I’m going to say that they were operational, religious, political and biological. Operationally you can see the problems that would emerge in a place like Afghanistan, and why that would be a recalcitrant place for public health officials to attempt to eradicate a disease as entrenched as polio. War and lack of security made vaccination campaigns dangerous and sometimes impossible. But let’s look for a moment at a different place. And this is a map of Nigeria, if you imagine the country, and that’s the state I want to talk about, the state of Kano in northern Nigeria. There we see a problem that’s political and religious.

Muslim leaders in Kano — and that’s in a country — the government of Nigeria is Christian-dominated. The states of northern Nigeria, however, are Muslim, and they were suspicious in northern Nigeria about Western intentions, especially after the launching of war in Afghanistan and Iraq, and people began to preach, religious leaders, that oral polio vaccine, these drops were not a measure of public health, but instead a sinister plot to sterilize Muslim children by poisoning them, so that Islam would recede from the earth and Christianity could replace it. And this whole thinking was ramped up by the issue raised by the pharmaceutical giant Pfizer, which had conducted unethical testing in Nigeria, in a way that inflamed public opinion especially, and led to a major lawsuit against the company.

Furthermore, since the traditional dogma about poliomyelitis held that it was an insignificant public health problem in the tropical world, it was difficult for many to understand why the international community was so intent on trying to rid Nigeria of polio. The Nigerians themselves regarded other disease as much greater causes of death and suffering. Why was the international community not concentrated on dealing with malaria, tuberculosis and HIV/AIDS? Why all this attention to polio, that seemed to them a relatively minor problem? The Emir of Kano was unable to discern benign intentions also when it transpired that industrial, predominantly Christian nations, were vaccinating their own populations instead with Salk’s vaccine — that is, the IPV — while insisting that Nigerians receive the oral vaccine. Why on earth was that?

Finally, opposition to the vaccination campaign, promoted by the Christian-dominated federal government of Nigeria, served as a proxy for sectional, political and religious discontents in the minority northern states. So, the result was a boycott of the anti-polio campaign, and it lasted until 2004, at which time Muslim operated laboratories in Indonesia agreed to supply vaccines to Nigeria, and other Muslim operated laboratories in India analyzed the vaccine previously supplied to Kano, and found it to be harmless, at which point prominent Muslim leaders around the world pressed their co-religionists in Nigeria to support the international effort. But by then considerable harm had been done to the campaign. It was not clear either that large numbers of Muslim parents would ever again allow their children to be immunized, or that the spread of the virus beyond Nigerian borders was something that could be reversed.

Let’s say that deals then with political and religious obstacles. Then there were biological ones. And to illustrate those, let me go somewhere else. And this is Uttar Pradesh, in a Muslim-dominated state in India. And again you see there the issue of Muslim suspicions and resistance to vaccination. But I want to turn from those — imagine all of that going on — but I’d like to look at some biological issues that emerged in places like this. The first was whether polio turned out to be more complicated than smallpox. Because smallpox had only one serotype; poliovirus has types 1, 2 and 3, and there’s no crossover immunity from one to the other. So, it was a more complicated disease than smallpox. That was a first problem. And this emerged in the form of what kind of vaccine do you use; one that’s monovalent, attacking developing resistance against only one type of poliovirus, or polyvalent? Should it be try to immunize you at once against one, two, or all three types? It turned out that polyvalent vaccines, for complicated reasons, weren’t so effective. Another was a problem of monitoring and surveillance. 

Unlike smallpox, the vast majority of polio cases were asymptomatic. And then there was a problem called “interference”. Children were found to be vaccinated twenty and twenty-five times, and still not to have developed an immunity to polio. Why was that? It turned out that in unsanitary tropical conditions, the intestinal flora of other viruses, particularly enteroviruses, in the digestive tract, could be so dense that the poliovirus in the vaccine would be unable to establish an infection and therefore an immune response. There were other problems that emerged in these turbulent years, after 2003 — turbulent for the Global Polio Eradication Initiative. One was that live viruses, the Sabin poliovirus — remember, it’s a live vaccine — it was unlike the smallpox vaccine.

The smallpox vaccine, as you know, was a vaccine from cowpox, that had a crossover immunity to smallpox, and cowpox is not a serious human disease. With polio instead, what’s administered through the oral vaccine is a live virus; in attenuated strains, yes, but it still is the live virus, and therefore there is always the possibility of the virus mutating and reverting to a virulent form. And this indeed happened, causing outbreaks of what’s called vaccine-associated paralytic polio. This possibility wasn’t just theoretical. It happened in the Philippines, in Madagascar, in China and in Indonesia.

Reversing progress against the disease, outbreaks of that kind occasioned a quip. The quip was that it was impossible to eradicate polio without the oral polio vaccine. But it was also impossible to eradicate polio with it because the vaccine itself led to outbreaks of polio. So, vaccine-associated poliovirus implied something serious, that the campaign against poliomyelitis could have no logical endpoint, because it would always be necessary to immunize populations against epidemics that could be initiated by the vaccine itself. A very paradoxical situation. And the difficulty is all the more intractable because people with immunodeficiency disorders can continue to shed the virus for as long as ten years or more. If the campaign were ever allowed to lapse, the accumulation of non-immunized susceptibles could result in devastating virgin soil epidemics among those who had no immunity.

So, for this reason critics have argued that the WHO campaign involved a semantic trick with the word “eradication.” Traditionally, eradication had always implied the cessation of the need to maintain public protective public health policies. But vaccine-associated polio, paralytic polio, meant that planners for this campaign would have to continue immunization indefinitely. The traditional criterion that eradication implied the end of prophylactic measures was quietly dropped. And then there are the problems about certification and eradication.

Poliovirus is notorious for being silent and undetected in its circulation, at the other end of the spectrum from smallpox. So, how would you be able to actually confirm that there were no more cases? And it’s also true that another problem, that symptoms of paralytic- acute flaccid paralysis can be caused by other conditions. They’re on your handout. I won’t mention them because I’m rapidly running out of time. But in my last thirty seconds I would say that the history of Global Polio Eradication Initiative demonstrates that the original optimistic belief, that polio, like smallpox, can be readily eradicated by vaccination, was misplaced.

Smallpox is exceptionally vulnerable to attack. It has no animal reservoirs, no range of serotypes that confer no crossover immunity. Its symptoms were almost always memorable and florid for the sufferer. It gives rise in survivors to a lasting immunity, and the vaccine used to attack it is effective after a single effort. Polio is a far more formidable enemy that reminds us that the original eradicationist perspective may be illusory. The human condition is to be surrounded by near infinity of infectious, constantly evolving microbes. Occasional final victories are possible, but they should be celebrated as exceptions, rather than regarded as successive steps to a disease-free Eden.

The normal state is one of vigilance, to minimize harm and achieve control. Polio seems to me unlikely soon to follow smallpox by becoming the second infectious disease ever to be eradicated. That would be — if I had time, I’d talk more about it. But I don’t. So, let’s stop there. And I don’t want to make a prediction, but I think we need to see how complex eradication actually is. And polio isn’t like smallpox; and many other diseases aren’t.

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