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This is the first in a 3 part series on polio. In this post I will cover basic information and history of the disease, as well as the early history of the polio vaccine.  To me, understanding the disease is extremely important, because how can we know if a vaccine is beneficial or not if we don’t have an accurate view of the disease it’s supposed to protect against?

The common line of thought in mainstream medicine is that polio was a horrible disease which afflicted many people in the early to mid 20th century. It was so rampant that even one of the most beloved presidents, Franklin Delano Roosevelt, was thought to have suffered from this disease. When a vaccine was produced for polio, it was deemed a miracle. Finally there would be an end to all these countless cases of paralysis sweeping through the country. The CDC tells us that the vaccine proved to be very effective, and is heralded as one of the best examples of how vaccines are our salvation from these horrible childhood diseases. Here is a common sentiment among the pro-vaccine crowd: 

If you read enough pro-vaccine articles, you’ll start to see the common assertion that we need to vaccinate so we can eradicate the disease, just like we got rid of polio. To many it seems pretty clear that the polio vaccine was a great achievement in medicine, and it is used as justification to push every other vaccination. I hate this argument, specifically because it encourages a rash generalization of all vaccines being equivalent. They are far from being equal, and it is my belief that each disease/vaccine needs to be evaluated on its own.

What is Polio?

The first thing we need to do is find out more about the disease that we’re trying to protect against. How can we know how effective and beneficial a vaccine has been, unless we know how bad the disease was? From the World Health Organization, we get this:

“Polio is a highly infectious disease caused by a virus. It invades the nervous system, and can cause total paralysis in a matter of hours. The virus enters the body through the mouth and multiplies in the intestine. Initial symptoms are fever, fatigue, headache, vomiting, stiffness in the neck and pain in the limbs.”(1)

Polio virus is transmitted via fecal-oral, oral-oral, or occasionally through a common vehicle such as a shared drink.There are actually three strains of polio virus, and you can technically get polio three times, because immunity to one strain does not confer immunity to the others. The most common outcome when a person is exposed to the wild polio virus is asymptomatic infection (~72%). What about the other 28%? What sort of symptoms do they get? 24% get abortive poliomyelitis, which is a minor illness. And 4% get non-paralytic poliomyelitis, which can include aseptic meningitis.(2)

According to the CDC, the clinical picture is even better:

“Up to 95% of all polio infections are inapparent or asymptomatic.”

“Approximately 4%-8% of polio infections consist of a minor, nonspecific illness without clinical or laboratory evidence of central nervous system invasion. This clinical presentation is known as abortive poliomyelitis, and is characterized by complete recovery in less than a week. Three syndromes observed with this form of poliovirus infection are upper respiratory tract infection (sore throat and fever), gastrointestinal disturbances (nausea, vomiting abdominal pain, constipation or, rarely, diarrhea) and influenza-like illness. These syndromes are indistinguishable from other viral illnesses.

“Nonparalytic aseptic meningitis (symptoms of stiffness of the neck, back, and/or legs), usually following several days after a prodrome similar to that of minor illness, occurs in 1%-2% of polio infections. Increased or abnormal sensations can also occur. Typically these symptoms will last 2 to 10 days, followed by complete recovery.”(3)

So the vast majority of polio infections will have no residual effects, and complete recovery is expected. In fact, up to 95% will be either asymptomatic, or a minor illness. The main reason for a vaccine seems to be to prevent the paralytic consequences of infection. Well just how often does paralysis occur?

“Only 1/1,000 to 1/100 infected individuals develop paralytic disease (28-30). Reports of greater ratios of paralytic infection to subclinical infection in poliomyelitis are not based on consistent case ascertainment, or are not representative of the range in the majority of literature reports.” (2)

“Up to 95% of all polio infections are inapparent or asymptomatic. Estimates of the ratio of inapparent to paralytic illness vary from 50:1 to 1,000:1 (usually 200:1). Infected persons without symptoms shed virus in the stool and are able to transmit the virus to others.”(3)

These sources both confirm that the estimates of paralytic infection may vary, but 1/200 is the generally accepted estimate. So if your child is infected with the polio virus, there is a 0.5% chance that they will get a paralytic infection. Put another way, there is a 99.5% chance that they will not have a paralytic infection. Still, from a public health standpoint, 1 case in 200 infections is a fair amount. And according to the CDC, in the pre-vaccine era there were an estimated 3 to 4 million infections per year, which equates to 15000 – 20,000 paralytic cases per year just in the US.

“Many persons with paralytic poliomyelitis recover completely and, in most, muscle function returns to some degree. Weakness or paralysis still present 12 months after onset is usually permanent.”(3)

Now we find that even in paralytic cases, it’s not typically permanent.

“The illness progresses to flaccid paralysis with diminished deep tendon reflexes, reaches a plateau without change for days to weeks, and is usually asymmetrical. Strength then begins to return.”(3)

Again, the CDC reaffirms that in paralytic cases, the paralysis is often not permanent.  After as little as days, strength can start to return. This fact is going to be useful for us to remember as we look into the history and diagnosis of polio.


Early History of Polio

Was polio always such a problem to society? When we look at the literature, we find that polio was a relatively benign disease prior to the 20th century, with only rare instances of paralytic infections. The CDC states:

“Before the 18th century, polioviruses probably circulated widely. Initial infections with at least one type probably occurred in early infancy, when transplacentally acquired maternal antibodies were high. Exposure throughout life probably provided continual boosting of immunity, and paralytic infections were probably rare.

In the immediate prevaccine era, improved sanitation allowed less frequent exposure and increased the age of primary infection. Boosting of immunity from natural exposure became more infrequent and the number of susceptible persons accumulated, ultimately resulting in the occurrence of epidemics, with 13,000 to 20,000 paralytic cases reported annually.”(3)

I want to point out that this excerpt from the CDC pinkbook mentions the sanitation theory, which we will come back to a little later. The CDC goes on to say:

“In the early vaccine era, the incidence dramatically decreased after the introduction of inactivated polio vaccine (IPV) in 1955. The decline continued following oral polio vaccine (OPV) introduction in 1961. In 1960, a total of 2,525 paralytic cases were reported, compared with 61 in 1965.”(3)

A few other sources corroborate the fact that polio prior to the 20th century was a much different disease:

“In reviewing this subject briefly, one finds that at the turn of the century, “infantile paralysis,” as it was then called, was considered to be “rather rare after the age of six.” Indeed more than 50 per cent of the cases were under two years of age.”(4)

“Early records (1900-1920) are scanty, in fact poliomyelitis did not become a reportable disease in Connecticut until 1916. Not until 1920 did the reports become adequate for analysis. Consequently the study was limited to the period from 1921 to 1947.”(4)

This is what the World Health Organization (WHO) had to say:

“The history of poliomyelitis suggests that in the first half of the 19th century the clinical disease was rare and largely restricted to infants, while epidemics were almost unknown.”(5)

So to summarize, the CDC and various other sources say that before the turn of the century, paralytic infections were probably rare, but for some reason we find a dramatic rise in paralytic cases in the early to mid 20th century. The CDC states that this is likely due to the sanitation theory. They then go on to talk about the dramatic decline in paralytic cases after the introduction of the vaccines. It seems pretty straightforward so far.

History of Polio Vaccines

When looking at the development of the polio vaccines, there are quite a few details we could go over, but I feel that may be information overload for a lot of people. Instead I’m just going to give a brief overview of some main events.

In 1954 there was a massive polio vaccine trial which tested the Salk polio vaccine in 1.8 million children. The Salk vaccine was an inactivated polio vaccine (IPV) meaning that the virus was killed. In 1955, the results of this trial were reported and it was stated that the vaccine was 80-90% effective in protecting against paralytic polio. In 1955, the Salk vaccine was licensed in the US and mass vaccinations begun. An interesting tidbit on the Salk vaccine involves what is known as the Cutter Incident.

“In April 1955 more than 200 000 children in five Western and mid-Western USA states received a polio vaccine in which the process of inactivating the live virus proved to be defective. Within days there were reports of paralysis and within a month the first mass vaccination programme against polio had to be abandoned. Subsequent investigations revealed that the vaccine, manufactured by the California-based family firm of Cutter Laboratories, had caused 40 000 cases of polio, leaving 200 children with varying degrees of paralysis and killing 10.”(8)

This incident occurred in April of 1955, shortly after the Salk vaccine was licensed. The US Surgeon General recommended suspending all polio vaccines, and mass vaccinations didn’t begin again until the fall of 1955. The Sabin oral polio vaccine (OPV) was first licensed in 1961, but it wasn’t until 1963 when the trivalent vaccine was licensed. The OPV quickly replaced the IPV as the vaccine of choice in the United States.

Why the two different vaccines? Sabin was critical of Salk’s vaccine, because he didn’t think that a killed-virus vaccine would offer lasting immunity. Sabin’s approach was to use a vaccine with a live-attenuated virus. After Sabin did clinical trials on his vaccine in Russia, it was found that his oral polio vaccine was better than the IPV for several reasons. It conferred longer-lasting immunity, so booster shots were not necessary. It was taken orally, typically on a sugar cube, rather than having to be injected, so it was much easier to administer. But one of the most intriguing advantages of the Sabin vaccine was the concept of passive vaccination. People receiving the OPV would still develop an active infection and shed the virus in the stool, and it was thought that this would help protect people who had not received the vaccine.

By the mid to late 1960’s a risk of the Sabin vaccine was discovered. It was possible for the weakened virus in the OPV to cause paralytic polio. Despite this knowledge, use of the Sabin polio vaccine continued in the US until the year 2000, when it was replaced with the IPV, which does not cause paralysis. Apparently, health officials at the time thought that the benefits of the OPV outweighed the small risk of vaccine associated paralytic poliomyelitis (VAPP).

Sanitation Theory

The CDC makes mention of the sanitation theory as an explanation for why we saw a huge increase in paralytic cases in the 20th century. The sanitation theory is a paradoxical theory in that disease incidence rises with improved sanitation. This theory proposes that as sanitation practices became better in the developed countries, exposure to the polio virus as infants, when we were still protected by maternal antibodies, declined. This led to exposure to the virus later in life when we have less protection, and there is a higher likelihood of developing serious sequelae (paralysis). Although this theory does seem to explain why polio, which used to be considered a fairly benign disease with only rare cases of paralysis, started to become more and more serious, there is some doubt as to whether it is accurate.

This theory is based on data researched by Albert Sabin (the same guy who invented the oral polio vaccine).(6) He found that the rates of paralytic infection varied. During 1944 and 1945 in the Phillipines, the rate of paralytic infections was 88 and 43 per 100,000 amongst the American troops, and either no cases or very rare instances among the Filipino children. Another example comes from the statistics from Hawaii between 1938 and 1947. Rates of paralytic disease were 10.2 per 100,000 in the white population, and 1.3 per 100,000 in the Hawaiian population.(6) These and several other observations were made back in 1951, and one of the conclusions made by Sabin was

In general, the poorer the population, its standard of living and sanitation, the more extensively is poliomyelitis virus disseminated among them and the lower is the incidence of paralytic poliomyelitis when virulent strains of virus come their way.”(6)

Based on this theory, we should have been able to predict that areas with poorer sanitation will have fewer issues with epidemics of paralytic paralysis. However, we find that even in areas with poor sanitation, these groups of people who previously seemed to have low rates of paralytic poliomyelitis started to experience epidemics. An example is an outbreak in Leopoldville starting in 1958. “There has been . . . a rate of 19.4 cases per 100,000 inhabitants.” What were the sanitary conditions? From the same article, we read “people live in huts and shacks with few sanitary facilities.” In fact 73% of the housing used pit privies. There was no indoor plumbing.(7)

The mindset today in developing countries that still lack proper sanitation and yet are experiencing epidemics of polio is summed up nicely in a recent article from 2011:

“Environmentalists and health, water and sanitation experts were of the opinion that Pakistan’s efforts for polio eradication and achieving sustainable development goals are bound to fail, if access to safe sanitation in the country is not improved.”(9)

We find more evidence that epidemic polio started to occur in places which still lacked proper sanitation. According to the Global Polio Eradication Initiative:

“Lameness surveys during the 1970s revealed that the disease was also prevalent in developing countries.”(10)

So what happened? Were the earlier observations just wrong? Or did something happen to change the fact that developing countries that still lack proper sanitation were now experiencing polio epidemics where previously they had none? The actual data doesn’t seem to fit the sanitation theory very well. At the very least, sanitation is not the only factor that affects the prevalence of paralytic polio.

My next post will look at some of the other factors affecting the prevalence of paralytic polio, as well as some diagnostic issues surrounding polio and vaccination.



(1)     World Health Organization. Media Centre. Fact Sheets. Poliomyelitis. http://www.who.int/mediacentre/factsheets/fs114/en

(2)      Differential Diagnosis of Acute Flaccid Paralysis and Its Role in Poliomyelitis Surveillance, Arthur Marx, Jonathan D. Glass, and Roland W. Sutter. Epidemiologic Reviews, Vol. 22, No. 2, 2000. http://epirev.oxfordjournals.org/cgi/reprint/22/2/298.pdf

(3)     Epidemiology and Prevention of Vaccine-Preventable Diseases, The Pink Book: Course Textbook, 11th Edition (May 2009), Chapter 16, Poliomyelitis. http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/polio.pdf

(4)     http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2598936/pdf/yjbm00342-0025.pdf

(5)     http://whqlibdoc.who.int/monograph/WHO_MONO_26_%28part5%29.pdf

(6)     http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1525657/pdf/amjphnation00428-0010.pdf

(7)     http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2555313/pdf/bullwho00332-0012.pdf

(8)     http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1383764/

(9)     http://www.thenews.com.pk/Todays-News-6-143915-Polio-eradication-not-possible-sans-improving-sanitation-experts

(10)  http://www.polioeradication.org/Polioandprevention/Historyofpolio.aspx