Polio or poliomyelitis is a severe infectious viral disease, usually affecting children or young adults that inflame the brainstem and spinal cord, sometimes leading to loss of voluntary movement and muscular wasting. It was a worldwide epidemic until the discovery of effective vaccines in the 1950s.
Jonas Salk’s Discovery of Polio Cure – Injectable Polio Vaccine
The American medical researcher Jonas Salk of the University of Pittsburgh discovered a cure for polio in 1952. He developed an injectable polio vaccine (Salk vaccine) which is made up of inactivated poliovirus strains: Mahoney (type 1 poliovirus), MEF-1 (type 2 poliovirus), and Saukett (type 3 poliovirus). These strains are cultivated in a monkey kidney tissue culture, which are then inactivated with formalin. Salk vaccine confers immunoglobulin-G mediated immunity in the blood stream, which protects the body from polio infection.
Salk vaccine underwent 3 years of field trial in few U.S. states. The result of the field trial was released in April 12, 1955. The Salk vaccine was found to be 60-70% effective against type 1 poliovirus, 90% effective against type 1 and type 2 poliovirus, and 94% effective against bulbar polio. Soon after Salk vaccine got its license, mass vaccination campaigns in children were launched in the United States. Since the start of mass vaccination campaigns, the annual number of polio cases fell from hundreds of thousands to just 5,600 in 1957 and 161 in 1961. Other countries in the world soon use Salk vaccine in their mass vaccination campaigns leading to the near eradication of polio disease.
Mass polio vaccination, Image from Wikimedia Commons
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Albert Sabin’s Discovery of Polio Cure – The Oral Polio Vaccine
The popularity of Salk’s injectable vaccine declined with the development and introduction of oral polio vaccine. The vaccine is made up of live-attenuated polio viruses – viruses that became less virulent due to spontaneous mutation in their genome. There were several groups that develop attenuated oral polio vaccine which include Hilary Koprowski group, H. R. Cox group, and Albert Sabin group. The vaccines developed by these groups were evaluated by a special committee created by the National Institutes of Health (NIH) in 1958. The vaccines were evaluated in terms of their ability to confer polio immunity and low incidence of neuropathogenicity in monkeys. Based on the findings of NIH committee, Sabin’s vaccine was chosen for worldwide distribution.
Licenses of oral polio vaccines were granted in 1961 (for type 1 & type 2 monovalent oral polio vaccine), 1962 (for type 3 oral monovalent polio vaccine), and 1963 (for trivalent oral polio vaccine). Between 1962 and 1965, an estimated 100 million Americans received Sabin’s oral vaccine in mass vaccination campaigns. As a result of these campaigns, there was a substantial decline of polio cases in the United States. Albert Sabin’s oral polio vaccine then became the vaccine of choice of countries worldwide.
As of 2008, polio remains endemic in only four countries: Afghanistan, India, Nigeria, and Pakistan.[ad#afterpost]