The inactivated polio vaccine (IPV) was first licensed in the US in 1955.
The oral polio vaccine (OPV) was developed in 1961.
Excerpts from the full paper:
If the vaccine was not as effective, one might wonder why the tremendous reduction occurred n the 1955, 1956, and 1957 reported rates. Here again, much of that reduction was a statistical artifact.
Prior to 1954 any physician who reported paralytic poliomyelitis was doing his patient a service by way of subsidizing the cost of hospitalization and was being community-minded in reporting a communicable disease.
The criterion of diagnosis at that time in most health departments followed the World Health Organization definition: "Spinal paralytic poliomyelitis: Signs and symptoms of nonparalytic poliomyelitis with the addition or partial or complete paralysis of one or more muscle groups...
Laboratory confirmation and presence of residual paralysis was not required.
In 1955 the criteria were changed... unless there is residual involvement [paralysis] at least 60 days after onset, a case of poliomyelitis is not considered paralytic.
This change in definition meant that in 1955 we started reporting a new disease, namely, paralytic poliomyelitis with a longer lasting paralysis.
Furthermore, diagnostic procedures have continued to be refined.
Coxsackie virus infections and aseptic meningitis have been distinguished from paralytic poliomyelitis. Prior to 1954 huge numbers of these cases undoubtedly were mislabeled as paralytic poliomyelitis. 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.
There is still another reason for the decrease in the reported paralytic poliomyelitis cases in 1955-1957.
As a result of the publicity given the Salk vaccine, the public questioned the possibility of a vaccinated child developing paralytic poliomyelitis. Whenever such an event occurred, every effort was made to ascertain whether or not the disease was truly paralytic poliomyelitis.
In fact, I am certain that many health officers and physicians here will ask routinely if a child has been vaccinated when signs of poliomyelitis are present during the summer months. We have been conditioned today to screen out false positive cases in a way that was not even imagined prior to 1954.
As a result of these changes in both diagnosis and diagnostic methods, the rates of paralytic poliomyelitis plummeted from the early 1950's to a low in 1957.
It is now extremely difficult to get a Minnesota physician to make a. preliminary diagnosis and report of nonparalytic polio. We now know that aseptic meningitis has a much broader etiology than poliovirus. In 1956 in much of our so-called non paralytic polio, the etiology turned out to be Coxsackie b-5 virus, and in 1957 a staggering outbreak turned out to be Echo 9 virus.
