Polio is a viral illness that in 95% of cases is completely asymptomatic, meaning it produces no symptoms. In 1% of cases the virus invades the central nervous system, where it targets motor neurons, resulting in flaccid paralysis.
Poliovirus has been around since ancient times, but in the 1940s and 1950s more cases of paralysis emerged–1952 being the highest number of reported cases ever. What happened in the 1940s and 1950s that was different?
In 1945, DDT came on the US market, and immediately the pesticide / nerve agent was used in a variety of both commercial and domestic applications including entire communities, swimming areas, dairies and farms, streets, alleys, and inside the home.
DDT was thought to ‘prevent polio’ by killing ‘polio carrying insects’ (even though that’s not how it actually spread) so it was sprayed in large quantities during epidemics, in areas where people, especially children, would play. It’s toxicity to the central nervous system was unknown at the time.
In the 1940s, tonsillectomies were found to be a cause of respiratory paralysis due to bulbar polio.
In the 1950s, researchers found that DPT vaccination was linked with limb paralysis. Case-control studies confirmed that children with paralytic polio were more likely to have received a vaccination in the affected limb within the previous month. DPT vaccination during epidemics were halted. This would be known as provocation polio.
The first polio vaccine, known as the Salk vaccine, came out in 1955. By April, 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 program was called off.
In what would become known as the Cutter Incident, the faulty vaccine caused 40,000 cases of polio, leaving 200 children with varying degrees of paralysis and killing 10.
Then it was discovered that from 1955 to 1963, an estimated 10-30% of polio vaccines administered in the US to a total of 98 million people were contaminated with simian virus 40 (SV40) (the polio vaccine is made on monkey cell cultures), which was later found to cause cancer in humans.