Polio and Acute Flaccid Paralysis

In post one of this series on polio, a term was introduced: “Acute Flaccid Paralysis”. [1]

Acute Flaccid Paralysis is a term which applies to the exact clinical symptoms you would expect to see from poliovirus infection, but which are not necessarily caused by polioviruses. Paralytic polio is actually considered a sub-category in the broad umbrella of acute flaccid paralysis. See pages 300-312 [1] for a chart and summary of many other causes of AFP, a few of which are: Guillaine-Barre syndrome, Cytomegalovirus polyradiculomyelopathy, Acute transverse myelitis, Lyme borreliosis, nonpolio enterovirus and Toxic myopathies.

For many years the medical profession assumed that when they saw paralysis with a particular cluster of symptoms, it was poliomyelitis. The 1954 Francis Trials of the Salk vaccine [2] triggered a reconsideration of this assumption, and a major change in the diagnostic criteria.

How were polio cases counted in 1954?

In 1954 most health departments worked with the WHO definition:

“…Signs and symptoms of nonparalytic poliomyelitis with the addition of partial or complete paralysis of one or more muscle groups, detected on two examinations at least 24 hours apart.” [3, p. 88]

How were polio cases counted in 1955?

In 1955 the criteria were changed to conform more closely to the definition used in the 1954 field trials: residual paralysis was determined 10 to 20 days after onset of illness and again 50 to 70 days after onset. [3, p. 88]

Thus, simply by changes in diagnostic criteria, the number of paralytic cases was predetermined to decrease in 1955-1957, whether or not any vaccine was used. At the same time, the number of nonparalytic cases was bound to increase because any case of poliomyelitis-like disease which could not be classified as paralytic poliomyelitis according to the new criteria was classified as nonparalytic poliomyelitis. Many of these cases, although reported as such, were not non-paralytic poliomyelitis. [3, p. 88] (emphasis added)

It was after the SALK vaccine was introduced, when fully vaccinated people continued to get “polio”, that doctors started looking a lot more carefully at the viruses in individuals. Many viruses were found to cause paralysis, for example coxsackie B, enterovirus 71, etc. Read more

Polio 2010


Over the next few weeks, Inside Vaccines will be taking a closer look at Poliomyelitis infections, exploring aspects of the history of poliomyelitis; describing environmental factors that increase the incidence of paralytic polio; considering the history and efficacy of the vaccines used against polio; and finally, exploring the campaign to eradicate polio.
First, let’s look at some basic information.

When most people think of poliomyelitis, they think of children who had lameness and leg deformities, with their legs in braces, or lying in iron lungs (old-style breathing machines, or ventilators) because they couldn’t breathe. Most people link all paralysis and lameness solely to a group of viruses called POLIOMYELITIS. The World Health Organization describes polio:

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. One in 200 infections leads to irreversible paralysis (usually in the legs). Among those paralysed, 5% to 10% die when their breathing muscles become immobilized. [1]

Now for a more accurate picture of exactly what “poliomyelitis” is.

The poliomyelitis viruses fall within a class of viruses called “human enteroviruses” [2]. Polioviruses belong to the viral family Picornaviridae [3]. There are three types: 1 Brunhilde; 2 Lansing; and 3 Leon.   Amongst these types there are hundreds of different strains. Type 1 is considered the most serious virus, followed by type 2.

Technically, a person can “get” poliomyelitis 3 times, since the types do not give cross protection to each other, but in practice, having clinical polio three times is very rare.

How is poliomyelitis virus transmitted?

Poliomyelitis is transmitted by person-to-person spread through fecal-oral and oral-oral routes, or occasionally by a common vehicle (e.g., water, milk). [4]

What happens when people are exposed to polioviruses?

When non-immune persons are exposed to wild poliovirus, inapparent infection is the most frequent outcome (72 percent). [4]

Most people won’t even be aware that they were sick. Read more

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