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

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